UNIT ONE

TOPIC ONE: LIFESTYLE, HEALTH AND RISK

By Mugo (Mr)

WATER

- The chemical formula of water is H2O

- The atoms of water molecule are;

(i) 2 hydrogen atoms

(ii) 1 oxygen atom

- The structure of a water molecule is as follows:

- The positive and negative (+ and -) indicate that there are small amounts of positive and negative charge on

the water molecule.

- The shape of water molecule is triangular.

- The bonds that join atoms of water are called covalent bonds. A covalent bond is formed when electrons are

shared by atoms.

- Water molecules are joined by hydrogen bonds. One water molecule can be joined to 4 other water molecules

by hydrogen bonds as follows:

Stability of a water molecule 1

- Water molecule is stable but, its atoms are unstable.

- The outermost shell of hydrogen atom has 1 electron instead of 2, hence unstable. Oxygen atom has 6

electrons instead of 8 in its outermost shell, hence unstable. To form a stable water molecule, the 3 atoms must

share electrons and in the process covalent bonds are formed.

Dipole nature of water

- When electrons are shared between atoms, they are not shared equally between those atoms because some

nuclei of these atoms attract more electrons than others. In a water molecule, the nucleus of the oxygen attracts

more electrons than the two nuclei of the hydrogen atoms. So, oxygen is slightly negative while hydrogen

atoms are slightly positive.

- The condition where in a molecule one side is slightly positive and the other side is slightly negative is called

dipole and the molecule is called dipolar, so, a water molecule is dipolar.

Importance of water as a dipolar molecule.

1. Solvent for ionic and polar substances

2. Medium for chemical reactions.

3. Medium for transport of substances.

Water as a solvent for ionic and polar substances

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- Ionic and polar substances have charges.

- Examples of polar substances are amino acids whose polar groups are NH2 (Amine/amino group) and COOH

(carboxyl group): and sugars whose polar group is OH.

- Example of an ionic substance is sodium chloride whose ions are Na+ and Cl-.

- When ionic /polar substance is placed in water, the following takes place:

1. Attraction of the positive ions by the oxygen of water and the attraction of the negative ions by the

hydrogen atoms of water.

2. Separation of ions and polar groups

3. Hydration (surrounded by water molecules) of these ions and polar groups i.e. dissolved.

Water as a medium for chemical reactions

- When in solid, substances are not reactive.

- However, when they dissolve in water and separate into ions and polar groups, these ions and polar groups

freely move and hence they are chemically reactive.

Water as a medium for transport

- Water transports ionic, polar and non-polar substances.

- Water easily transports ions, and polar groups.

- However, non-polar substances (no charges) such as lipids combine with proteins to form lipoproteins so that

they are now transported by water

- The transport systems in organisms include:

1. Circulatory system – blood

2. Lymphatic system – lymph

3. Xylem vessels in plants – water and minerals

4. Phloem in plants – sucrose and amino acids.

Importance of hydrogen bonds in water

- When in large numbers, hydrogen bonds are very hard to break using heat.

- When hydrogen bonds between water molecules are broken, water is converted into vapour (individual water

molecules).

- Hydrogen bonds are formed between the negative charge of the oxygen atom (Oxygen atom has 2 negative

charges) and the positive charge of the hydrogen atom. Water, unlike CO2, is dipolar and therefore hydrogen

bonds form between water molecules, holding these molecules together forming liquid. This is why at room

temperature water is liquid and CO2 is gas.

PROPERTIES OF WATER DUE TO HYDROGEN BONDS

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1. Liquid at room temperature

- Due to its dipolar nature, hydrogen bonds are formed between water molecules hence; water remains liquid at

room temperature.

2. Cohesion

- This is attraction force between similar molecules.

- Hydrogen bonds hold H2O molecules together giving it cohesion.

- Cohesion is important to transport water and dissolved substances in the xylem, in a continuous unbroken

column.

3. Adhesion

- Attraction force between non-identical molecules e.g. water and xylem wall.

- Hydrogen bonds allow water to hold onto other substances e.g. to hold onto the walls of the xylem to allow

water to be transported in a continuous unbroken column in the xylem.

4. High specific heat capacity

- Specific heat capacity (SHC) is the amount of energy required to raise the temperature of 1kg of water by 10C.

- Water has a high SHC due to hydrogen bonds (it is not easy to raise the temperature of water to break strong

hydrogen bonds).

- So, the temperature of water remains relatively constant due to this property, whose biological importance

include;

a) The temperature of water bodies such as oceans remains relatively

constant for the survival of aquatic animals.

b) Stable temperature in living organisms so that enzymes remain stable.

5. Latent Heat of vaporation

- Latent heat of vaporization is the amount of energy required to convert liquid to vapour.

- Water has high latent heat of vaporization due to hydrogen bonds.

- The importance of this property of water is that water is a coolant (cooling agent), through sweating in

humans, transpiration in plants, panting in dogs and gaping in crocodiles.

6 High surface tension

- Surface tension is the tightness of water molecules on the surface forming a skin like layer due to hydrogen

bonds.

- The water molecules beneath the ones on the surface pull the ones on the surface inwards by hydrogen bonds,

creating a skin like layer.

- The biological importance of high surface tension of water is to create a surface onto which aquatic insects

such as pond skaters can land, move, feed and breed.

7. Unique freezing density

- The highest density of water is at 40C and not 00C.

- At 40C water is still liquid but at 00C it becomes solid (ice) which floats due to low density.

- When water freezes, hydrogen bonds strengthen and this causes the water structure to open up, increasing the

volume and decreasing the density i.e. water expands as it freezes.

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- The importance of this is that ice acts as a heat insulator so that the lower atmospheric temperature during

winter does not affect the water below the ice, hence the water below this ice remains relatively warm for the

survival of aquatic animals.

Summary of the properties of water

1. Dipolar nature of water, making it;

(i) An essential solvent for polar and ionic substances.

(ii) A transportation medium of substances.

(iii) A medium for chemical reactions.

2. Hydrogen bonds that make water to have the following properties;

(i) high specific heat capacity

(ii) high latent heat of vaporization

(iii) cohesion

(iv) adhesion

(v) liquid at room temperature

(vi) unique freezing density

EDEXCEL QUSTIONS ON WATER

June 2010 q1g

Jan 2014 1b

CARBOHYDRATES

- These are organic (carbon-containing) substances made up of 3 elements:

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i) Carbon

ii) Hydrogen

iii) Oxygen

- The 2 major groups of carbohydrates are:

a) Sugars – monosaccharides & disaccharides.

b) Non-sugars – polysaccharides.

a) Sugars

- These are sweet tasting.

- They are divided into 2:

(i) monosaccharides

(ii) disaccharides

MONOSACCHARIDES

- These are the simplest sugars.

- General formula for monosaccharides is CnH2nOn, where n is 3 to 9; from triose to nonose. - All monosaccharides consist of 2 reactive groups called;

a) Hydroxyl group (OH)

b) Carbonyl group (C=O)

- There are 2 forms of carbonyl groups called:

a) Aldehyde group (H-C=O)

A carbonyl group becomes an aldehyde group when a hydrogen atom is attached to it. It is this

aldehyde group that reduces metallic ions. A monosaccharide with an aldehyde group is called aldose

sugar e.g. glucose and galactose.

b) Ketone group

A ketone group is formed when the carbonyl group is between carbon atoms. It reduces metallic ions

but when it is converted first to aldehyde group. Monosaccharides with keto-groups are called ketose

sugars e. g fructose.

Note: so, monosaccharides are either;

a) Aldoses – glucose

b) Ketoses – fructose

Linear and ring forms of monosaccharides

- Linear forms are less stable but they reduce metallic ions because of availability of carbonyl groups.

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- Ring forms have molecular stability but cannot reduce metallic ions due to loss of carbonyl groups, so, in

Benedict’s test, heating the monosaccharide is meant to open up the ring form into the linear form to expose the

carbonyl groups that reduce the metallic ions.

Trioses

- They are the simplest monosaccharides.

- They are intermediates during photosynthesis and respiration.

- Example is glyceraldehyde

Pentoses

- They are monosaccharides.

- They are 5 carbon sugars.

- There are 2 main types of pentoses;

a) Ribose (C5H10O5)

b) Deoxyribose (C5H10O4)

- The difference between ribose and deoxyribose is that on carbon atom 2, ribose has OH group and deoxyribose

has just H group.

- The importance of pentoses include:

a) Synthesis of nucleic acids (DNA and RNA). DNA consists of deoxyribose while RNA consists of ribose

b) Synthesis of a nucleotide co-enzymes (hydrogen acceptors) such as NAD and FAD

c) Synthesis of energy carrier molecules such as ATP, ADP and AMP.

Hexoses

- These are monosaccharides.

- They are 6 carbon sugars.

- They consist of both linear and ring forms.

- Their chemical formula is C6H12O6.

- They are all respiratory substrates i.e. they are broken down to provide energy during respiration.

- The common hexoses are glucose, fructose and galactose

Glucose

- There are 2 isomers of glucose

a) - glucose

b) - glucose

- glucose - glucose

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Note

- In - glucose, OH on carbon atom One (C1) is below the ring or below carbon atom one (C1).

- In - glucose the, OH on carbon atom one (C1) is above the ring or above carbon atom one (C1).

- The importance of isomerism in glucose is that it gives different types of polysaccharides as follows:

a) Starch and glycogen are made up of glucose

b) Cellulose is made up of - glucose

- The importance of glucose include;

a) It is a respiratory substrate that provides energy when respired.

b) It synthesizes disaccharides and polysaccharides.

Fructose

- Fructose is a sugar which is present naturally in fruits, some vegetables and honey. The structure of

fructose is as follows:

- The importance of fructose

include;

a) It is a respiratory substrate that is respired to provide energy.

b) It synthesizes disaccharides – sucrose.

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c) It sweetens the fruits which attract animals, facilitating seed dispersal.

Galactose

- It occurs in our diet mainly as part of the disaccharide sugar called lactose (milk sugar)

- The importance of galactose include;

(i) Food for infants as a respiratory substrate.

(ii) Synthesis of disaccharide called lactose (glucose + galactose)

DISACCHARIDES

- The formula for disaccharide is CnH2n-2On-1, where n is 12- They are sugars made up of 2 monosaccharides.

- They are also called double sugars.

- The common disaccharides are;

(i) Maltose (malt sugar) Glucose + Glucose

(ii) Sucrose (cane sugar) glucose + fructose

(iii) Lactose (milk sugar) Glucose + galactose

- The chemical formula for all disaccharides is C12H22O11

Condensation reaction in the formation of disaccharides

- Condensation reaction involves a loss of water molecule when 2 monosaccharides join through a bond.

- In disaccharides, the bond that joins the monosaccharides together is called a glycosidic bond.

Hydrolysis reactions in breaking down disaccharides.

- Hydrolysis reaction involves the addition or gain of a water molecule to break down the glycosidic bond in

the disaccharide in order to get individual monosaccharides.

- There are 2 types of hydrolysis;

1. Acid hydrolysis

- The disaccharide is boiled with dilute acid to break down the glycosidic bond.

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2. Enzymatic hydrolysis

- The disaccharide is incubated with the enzyme to break the glycosidic bond as shown below;

Maltose maltase glucose + glucose

Sucrose sucrase glucose + fructose

Lactose lactase glucose + galactose

The following diagram shows the hydrolysis and condensation of maltose;

Maltose

- It is a disaccharide

- It is made up of 2 -glucose molecules

- Its chemical formula is C12H22O11

- It is mainly found in seeds. It is hydrolyzed into glucose and this glucose is respired to provide energy for the

germinating seeds.

- Digestion of starch in animals and germination in seeds release maltose because in both processes – starch is

hydrolyzed by amylase enzyme to get maltose.

Sucrose

- It is a disaccharide

- Made up of glucose and fructose

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- Chemical formula is C12H22O11

- Mainly found in sugar cane and sugar beet

- It is the form of carbohydrate transported in the phloem of plants.

Lactose

- It is a disaccharide

- Made up of glucose and galactose

- Its chemical formula is C12H22O11

- Mainly found in mammalian milk to provide energy for the infants when it is hydrolyzed.

Polysaccharides

- These are large molecules (polymers).

- They are made up of many glucose molecules which are joined by glycosidic bonds through condensation

reactions.

- The 3 common polysaccharides are;

1) Starch – energy storage molecule in plants.

2) Glycogen – energy storage molecule in animal cells (liver and muscle), bacteria and fungi

3) Cellulose – it is a structural carbohydrate that gives strength in the plant cell walls.

The structure of starch

- It is a polysaccharide

- It is made up of -glucose molecules

- These glucose molecules are joined by glycosidic bonds

- Starch consist of 30% amylose and 70% amylopectin

- Amylose consists of about 300 glucose molecules which are joined by 1, 4 glycosidic bonds. It is unbranched

hence has only 1, 4 glycosidic bonds. It is helical / coiled. It consists of 30% of starch. When iodine solution is

added, it turns blue black.

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- Amylopectin consists of about 1500 glucose molecules joined by 1, 4glycosidic bonds. It is branched thus has

also 1, 6 glycosidic bonds. These branches occur after every 20-30 glucose molecules. It is helical /coiled.

When iodine solution is added, it turns reddish brown. It consists of 70% starch.

NB

- 1-6 glycosidic bonds cause branching

- OH on carbon atom 2 attracts one another by H-bonds causing coiling/helical shape

- Coiling and branching makes the molecule compact so that many of them can be stored in small spaces (cell).

The following table gives differences between amylose and amylopectin

Amylose Amylopectin

Short (300 glucose molecules) Long (1,500 glucose molecules)

Unbranched hence only 1,4 glycosidic bonds Branched, hence has 1,4 and 1,6 glycosidic

bonds

30% starch 70% starch

Turns blue black with iodine solution Turns reddish brown with iodine solution

Less compact hence less amount of energy More compact hence more energy

These are the similarities between amylose and amylopectin;

1. Both are polysaccharides

2. Made of - glucose molecules

3. Glycosidic bonds join the glucose molecules.

4. Both are Coiled/helical

5. Energy storage molecules in plant cells

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Glycogen

- It is a polysaccharide

- Made up of - glucose molecules

- Glucose are joined together by glycosidic bonds

- It is branched, hence has 1, 4 and 1, 6 glycosidic bonds. Branches occur after every 8 to 12 glucose molecules

hence it is more compact than amylopectin.

- It is also coiled/helical because OH on carbon atom 2 attracts one another by H-bonds.

- It is an energy storage molecule in animal cells (liver and muscle cells), bacteria and fungi.

Note

Amylopectin (starch) and glycogen are energy storage molecules, they are both branched and coiled but glycogen

is more branched, hence more compact, therefore stores more energy.

Adaptations of starch (amylopectin) and glycogen as energy storage molecules;

1. Large – to store a lot of energy.

2. Large – so that they remain inside the cells.

3. Insoluble – so that they have no osmotic effect

4. Inert – no chemical reaction

5. Compact – so that many of them can be stored in a small space (cell) to provide a lot of energy.

6. Easily hydrolyzed by enzymes to release many glucose molecules when energy is needed.

EDEXCEL QUSTIONS ON CARBOHYDRATES

1) Jan2009 q32) June 2010 q1a, b, c3) June 2011 q2a4) Jan 2012 q45) June 2012 q26) Jan 2013 q67) Jan 2014 1ai8) Jan 2014 q6a

Lipids

- They are biological molecules made up of 3 elements;

(i) Carbon

(ii) Hydrogen

(iii) Oxygen

- They have less amount of oxygen than carbohydrates.

- They are insoluble in water but soluble in organic solvents such as ethanol.

- The 2 major groups of lipids;

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1. Simple – with glycerol only.

2. Complex – with glycerol and fatty acids.

- The complex lipids are;

1. Triglycerides – fats and oils

2. Phospholipids

3. Waxes

Triglycerides

- They are natural fats and oils.

- At room temperature, fats are solids and oils are liquids.

- Triglycerides are lipids made up of ;

(i) Three Fatty acids.

(ii) One glycerol molecule.

- These 3 fatty acids and glycerol are joined by ester bonds

- Each ester bond is formed in a condensation reaction/esterification reaction in which a water molecule is lost. The reaction

is catalyzed by an enzyme.

Glycerol

- The structure of glycerol is as follows;

- The chemical formula for a glycerol molecule is C3H8O3.

- There is only 1 type of glycerol molecule i.e. all glycerol molecules are the same.

Fatty acids

- Triglycerides consist of 3 fatty acids.

- There are different types of fatty acids which vary in the followings ways;

1. The length of the hydrocarbon chain, from 8-20 carbons.

2. The absence or presence of carbon –carbon double bonds.

3. The number of double carbon-carbon bonds.

4. The mix of fatty acids i.e. all the 3 are the same or all the 3 are different or any other combinations.

- A fatty acid is made up of 2 components;

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1. Carboxylic group (COOH)

2. Hydrocarbon Chain (CH2)n CH3.

- A fatty acid can be represented as follows

Formation of triglyceride

- Fatty acids join the glycerol molecule one at a time by an ester bond i.e. monoglyceride, diglyceride and triglyceride

- Formation of an ester bond is through condensation reaction where a water molecule is formed. To form water, glycerol

loses hydrogen and fatty acids losses OH.

Types of fatty acids

a) Saturate fatty acids

b) Unsaturated fatty acids

Saturated fatty acids

- They have the maximum number of hydrogen atoms and have only single carbon –carbon bonds in their hydrocarbon

chain.

- Saturation refers to the amount of hydrogen in the molecule.

- Triglycerides with saturated fatty acids are called saturated triglycerides.

- Due to lack of double carbon – carbon bonds in the hydrocarbon chain, there is no straining hence no kinking (bending)

and therefore they have high melting point, above 400C and therefore they remain solid at both room and body

temperatures.

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- Saturated fatty acids have double bond between carbon and oxygen in the carboxylic group.

- The following table summarizes examples of saturated fatty acids and the saturated triglycerides they are found in.

Fatty acids No of double C-C

bonds

Abundant in (saturated triglycerides) M.P

Palmitic 0 Palm oil 63

Stearic 0 Cocoa and animal fat 68

Lauric 0 Coconut oil and palm oil 44

- Stearic fatty acid has the following structure C17H33 COOH

Unsaturated fatty acids

- They have less number of hydrogen atoms and have at least one double carbon-carbon bond (C=C bond) in the

hydrocarbon chain. In addition, there is a double bond between carbon and oxygen in the carboxylic group.

- Due to double C-C bonds, there is straining, causing kinking that lowers the melting point and therefore they remain liquid

at both room and body temperature. The more the double C-C bonds, the more the straining, kinking and the lower the

melting point.

- There are 2 types of unsaturated fatty acids;

1. Mono-unsaturated fatty acids.

2. Poly-unsaturated fatty acids.

Mono-unsaturated fatty acids.

- They have a single double C-C bond in the hydrocarbon chain.

- Example is oleic fatty acid (C17H33COOH) whose M.P is 13.40C and is mainly found in olive oil.

- Another mono-unsaturated triglyceride in addition to olive oil is peanut oil.

Poly-unsaturated fatty acids

- They have more than one double covalent bonds (C=C) in their hydrocarbon tail.

- Example is linoleic fatty acid whose melting point is -40C and is mainly found in maize and sunflower.

- Other poly-unsaturated triglycerides include: fish oil, soya bean oil, cotton seed oil and sesame oil.

The following table summarizes the differences between saturated and unsaturated fatty acids:

Saturated Unsaturated

1. Maximum number of hydrogen atoms Low number of hydrogen atoms

2. Have only single C-C covalent bonds in

the hydrocarbon tail

Have double covalent bonds (C=C) in the

hydrocarbon tail

3. Have no kinks due to lack of double

covalent bonds hence has a straight chain

Have kinks due to presence of double covalent

bonds hence has a bent chain

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4. Solid at room temperature due to high

melting points

Liquids at room temperature due to low melting

points

Functions of triglycerides

1. Energy store

- Generates more than twice the energy generated by carbohydrates. Triglycerides are essential energy stores because of the

following properties;

a) Insoluble (no osmotic effect)

b) Generates a lot of energy due to long carbon chains.

c) Compact hence a lot can be stored in the cell.

2. Buoyancy in aquatic animals

- Buoyancy is the ability to float

- Triglycerides are less dense than water hence aquatic animals are able to float e.g. blubber in whales which contains oil.

3. Heat/thermal insulation

- Triglycerides are poor thermal conductors (poor conductors of heat) e.g. adipose tissue (tissue that stores a lot of fat

beneath the skin) reduces heat loss from the body.

4. Protection of delicate organs

- Triglycerides are soft and therefore cushion the delicate organs such as heart, lungs and kidneys so that they are not

damaged.

5. Sources of metabolic water when oxidized

- Metabolic water is important in desert mammals such as camels to supplement the little water they get.

Phospholipids

- A phospholipids is a molecule made up of:

a) 1 glycerol

b) 2 fatty acids

c) Phosphate group

d) Ester bonds join fatty acids to glycerol

e) Phospho-ester bond joins phosphate to glycerol.

1. Glycerol

2. Fatty acids

3. Phosphate group

- The summarized structure of phospholipids

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1- Phosphate heads

2- Fatty acids tail

- Phospholipids are used to synthesize biological membranes.

Cholesterol

- This is a lipid.

- Cholesterol is not a saturated fat but is made up in the liver from saturated fats absorbed from food.

- The structure of cholesterol is

- In the cell membranes cholesterol has 2 major roles;

1. Control fluidity so that the cell membrane is not too fluid or too rigid

2. Provides the mechanical strength to the cell membranes. So, the cell membranes with little or no cholesterol easily

break down.

EDEXCEL QUSTIONS ON LIPIDS

1. June 2009 q1a2. Jan 2011 q7a3. June 2012 q4bi,ii4. June 2013 q3a

Transport system in humans

- The 2 transport systems in humans are:-

1. Cardiovascular system

2. Lymphatic system

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- Humans do not rely on diffusion for the transport of substances in their bodies and therefore they need a

specialized transport system i.e. cardiovascular and lymphatic system. This is because humans have a small

surface area to volume ratio and therefore cannot rely on diffusion for transport of substances.

- In summary cardiovascular and lymphatic system are involved in mass transport of substances to

overcome the limitation of diffusion in meeting the requirements of the organisms.

- Small organisms such as amoeba have large surface area to volume ratio and therefore they rely on diffusion

for absorption and movement of substances.

- The following cubes illustrate the concept of surface area (SA) to volume ratio

S.A: Volume S.A: Volume

(2 x 2) 6: 2 x 2 x 2 (8 x 8) 6: 8 x 8 x 8

24:8 384:512

SA/V=24/8=3 SA/V=384/512=0.75

Cardiovascular system

- This is the mass transport system in humans.

- It consists of the heat (cardio) and the blood vessels (vascular).

- Circulation is the passage of blood through the blood vessels.

- The features of the mass transport system such as cardiovascular system include;

(i) A system of vessels that carries substances.

(ii) A way of making sure that substances are moved in the right (one) direction.

(iii) A means of moving materials fast enough to supply the needs of organism e.g. pumping of the heart

and the use of active transport.

(iv) A suitable transport medium e.g. blood, lymph

Functions of the cardiovascular system

1. It transports the requirements needed by the cells of the body e.g. glucose and oxygen.

2. It transports the waste products of metabolism from the cells e.g. urea and CO2.

3. It carries hormones from endocrine glands to target cells.

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4. It forms part of the defense system of the body.

5. It distributes heat throughout the body, hence maintains homeostasis.

The human heart

The structure of the human heart

- It is a muscular pumping organ.

- It is a double pump (right and left).

- It is made up of cardiac muscles (heart muscles).

- It has 4 chambers i.e. 2 atria and 2 ventricles.

- It is associated with the blood vessels and valves.

The heart as a double pump

- The human heart is a double pump.

- These 2 pumps are joined together and work in perfect synchrony.

- The right and the left pumps of the heart are separated by a septum.

- The right side of the heart (right pump) receives deoxygenated blood from the body via the vena cava, and it

pumps it to the lungs for oxygenation and removal of CO2 through the pulmonary artery.

- The left side of the heart (left pump) receives oxygenated blood from the lungs through pulmonary vein and

pumps it to the body via the aorta.

- The blood in the left side of the heart does not mix with the blood in the right side of the heart.

The cardiac muscle

- It is also called the muscle of the heart.

- It has a special property i.e. it contracts rhythmically without resting or fatigue.

- Atria have thinner cardiac muscles while ventricles have thicker cardiac muscles. However the left ventricle

has thicker muscles than the right ventricle.

Thickness of cardiac muscle

- The thickness of the cardiac muscles determines the distance through which blood is pumped. The thicker the

muscle, the more the contraction, the greater the pressure, and the longer the distance and vice versa, as

discussed below;

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a) Thin cardiac muscles of the atria

They pump blood to the shortest distance when they contract i.e. from the atria to the ventricles

via atrio-ventricular valves (AV valves) i.e. tricuspid and bicuspid (mitral) values.

As the blood enters the atrium via vena cava and pulmonary vein, due to its weight, the A.V

valves open and allow two-third of the ventricles to be filled passively with blood so that the

contraction of the atria tops up the blood in the ventricles.

b) Thick muscles of the right ventricle

When it contracts, it pumps blood to the lungs via pulmonary artery and back to the left atrium

via pulmonary vein. This circulation of blood from the heart to the lungs and back to the heart

is called pulmonary circulation.

c) Thicker muscles of the left ventricle

These muscles contract powerfully to generate more pressure that pumps blood from the left

ventricle to the body via the aorta and back to the right atrium via the vena cava. This

circulation of blood from the heart to the body and back to the heart is called systemic

circulation.

Functions of thicker cardiac muscles of the left ventricle;

1. To pump blood to all parts of the body.

2. To overcome the effect of elastic recoil.

3. To overcome the combined resistance of multiple capillary networks.

Double circulation in humans

- This means that the blood flows through the heart twice in one circulation.

- It involves pulmonary circulation (circulation of blood from the heart to the lungs and back to the heart) and

systemic circulation (circulation of blood from the heart to the boy and back to the heart).

NB

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Fish have single circulation where blood flows from the body to the heart, then from the heart to the gills and from

the gills it does not flow to the heart but it flows to the body. So, it flows to the heart once in a single circulation.

Advantages of double circulation in humans;

1. Allows differential pressure between the lungs and the rest of the body so that the lungs have low pressure

of blood and the body has high pressure:

Low pressure in the lungs ensures that there is enough time for the blood to absorb O2

&remove CO2, prevents the capillaries from bursting and to prevent ultra filtration.

High pressure in the body ensures that the blood reaches all parts of the body, it overcomes the

effects of elastic recoil and the effects of the combined resistance of multiple capillary

networks.

2. Repressurization of blood due to further pumping by the heart so that the requirements can be moved to

the body faster and the wastes can be moved to the lungs faster.

3. No mixture of oxygenated and deoxygenated blood. Oxygenated blood is in the left side and deoxygenated

in the right side.

4. Muscles of mammals need a lot of oxygen and double circulation serves this purpose.

Blood vessels associated with the heart

1. Inferior vena cava – it carries deoxygenated blood from the lower part of the body to the right atrium.

2. Superior vena cava – it carries deoxygenated blood from the head, neck, arms and chest to the right atrium.

NB: vena cava is the largest vein

3. Pulmonary artery – together with umbilical cord arteries, they are the only arteries that carry deoxygenated

blood. It carries deoxygenated blood from the right ventricle to the lungs for the removal of CO 2 and

absorption of O2. At the base of the pulmonary artery there is a valve called pulmonary (right) semi-

lunar valve whose role is to prevent the back flow of blood from the pulmonary artery back into the right

ventricle.

4. Pulmonary vein – together with umbilical cord vein, they are the only veins that carry oxygenated blood. It

carries oxygenated blood from the lungs to the left atrium.

5. Aorta – this is the largest artery. It carries oxygenated blood from the left ventricle to the body in order to

deliver requirements such as oxygen to the tissues. At the base of aorta, there is a valve called aortic (left)

semi-lunar valve that prevents the backflow of blood from the aorta back into the left ventricle.

6. Coronary arteries- These are right and left coronary arteries that supply the heart muscles with

requirements. They are the first arteries to branch from the aorta.

VALVES ASSOCIATED WITH THE HEART

They are atrio-venticular valves found between the atria and the ventricles. These are;

1) Bicuspid valve (or mitral valve)

- it is found between the left atrium and the left ventricle.

22

- its functions are:

a) allows blood to flow from the left atrium into the left ventricle.

b) Prevents the backflow of blood from the left ventricle to the left atrium during ventricular

systole, so that the blood enters the aorta.

2) Tricuspid valve

- It is found between the right atrium and the right ventricle.

- Its functions are;

a) It allows blood to flow from the right atrium into the right ventricle.

b) It prevents the backflow of blood from the right ventricle in the right atrium so that the

blood enters the pulmonary artery.

The external and internal structures of the human heart

23

Summary of the blood flow through the heart; 24

1. Vena cava

2. Right atrium

3. Tricuspid valve

4. Heartstrings (tendons)

5. Papillary muscles

6. Right ventricle

7. Right/pulmonary semi-lunar valve

8. Pulmonary artery

9. Lungs

10. Pulmonary vein

11. Left atrium

12. Bicuspid valve

13. Left ventricle

14. Left/aortic semi-lunar valve

15. Aorta

16. Body

17. Septum

Control of the opening and closing of the atrio-venticular valves (AV valves)

25

- Heartstrings prevent the valves from inverting (turning inside out) during ventricular systole.

- The papillary muscles adjust tension in the heartstrings, i.e. they contract to pull on tendons and close the

valves.

- When the papillary muscles relax, the heartstrings loosen/slacken to open the valves.

- Papillary muscles contract when ventricles contract (ventricular systole) and they relax when the heart relaxes

(diastole).

The heart sounds

- These sounds are made when the blood hits the AV valves and the semi-lunar valves.

- These 2 sounds of the heart are described as lub and dub

- The first sound (lub) comes when the AV valves close and the blood hits against these valves during

ventricular systole.

- The second sound (dub) comes as the backflow of blood hits the semi-lunar valves in the pulmonary artery and

aorta, as ventricles relax.

How cardiac muscles are supplied with requirements;

- This is called coronary circulation.

- The first arteries to branch from the aorta are right and left coronary arteries that further branch into arterioles

and finally branch into capillaries that penetrate deep into the cardiac muscles.

- Through diffusion, the requirements such as glucose and oxygen enter the cardiac muscle through capillary

walls.

How the heart muscles removes wastes

- This is called coronary circulation.

- Through diffusion, wastes such as urea and CO2 from the cardiac muscles enter the capillaries.

- These capillaries join to form venules (small veins) that further join to form cardiac veins that lead to blood

spaces called blood sinuses that then drain deoxygenated blood into the right atrium.

Heart beat

- The beating of the heart produces sound called the heart beats.

- These sounds are lub and dub.

- The rate of the heart beat shows how fast the heart is contracting.

Factors that affect the heart rate

26

- Heart rate is the number of heart per minute.

- An average adult has a heart rate of about 70 beats per minute.

- The following factors affect the heart rate

(i) Physical exercise – during exercise tissue need more O2 and glucose and so the heart must beat faster to

supply them with these requirements and to remove the waste.

(ii) Permissible drugs – these include caffeine and nicotine that raise the heart rate .

(iii) Illegal drugs – they raise the heart rate.

(iv) Stress and excitement – they raise the heart rate due to the production of adrenaline.

(v) Rest and relaxation – they lower the heart rate.

(vi) Age – in small children it is much higher than adults.

(vii) Temperature - the higher the temperature, the higher the heart rate.

Cardiac cycle

- It is the sequence of events that take place in one heart beat and it last for 0.83 second. It is initiated at the sino-

atrial node (SAN) also called pacemaker. These events are: Atrial systole (0.1s), ventricular systole (0.3s) and

complete cardiac diastole (0.4s).

Events of the cardiac cycle

1. Atrial systole

- This is the contraction of the atria when they are filled up with blood.

- Its role is to pump blood into the ventricles from the atria via AV valves.

- It lasts for about 0.1s.

- During atrial systole, AV valves are opened.

- During atrial systole, semi-lunar valves are closed.

- During atrial systole, atria are contracted and ventricles are relaxed.

2. Ventricular systole

- This is the contraction of the ventricles when they are filled up with blood.

- Its role is to pump blood into the aorta and the pulmonary artery from the ventricles.

- It lasts for 0.3s

- During ventricular systole, the AV valves close to prevent the backflow of blood from the ventricles into the

atria and to build up pressure in the ventricles.

- During ventricular systole, semi-lunar valves are forced to open.

- During ventricular systole, atria are relaxed and ventricles are contracted.

3. Diastole (Complete cardiac diastole)

27

- This is the relaxation of the heart after ventricular systole.

- During diastole the whole heart is relaxing, reducing pressure in the heart so that blood flows into the atria via

the vena cava and pulmonary vein, hence refilling the heart with blood.

- So, the role of the diastole is to refill the heart with blood.

- It lasts for 0.4 second.

- During diastole, the AV valves open.

- During diastole the semi-lunar valves are closed.

Pressure changes in the left part of the heart during cardiac cycle.

- During the left atrial systole, the atrial pressure is greater than the left ventricular pressure because of the

refilling of the left atrium by the blood from the pulmonary vein.

- The blood enters the left ventricle.

- When the pressure of the left ventricle exceeds the pressure of the left atrium, the bicuspid valve closes to

prevent the backflow of blood from the left ventricle into the left atrium.

- The pressure of the left ventricle rises suddenly and forces open the left semi-lunar valve

- The pressure in the aorta begins to rise but still it is less than the pressure in the left ventricle.

- When the pressure in the aorta exceeds the pressure in the left ventricle, the left semi-lunar valve closes to

prevent the backflow of blood to the left ventricle from the aorta.

- This causes the pressure in the left ventricle to suddenly drop causing relaxation of the heart (diastole) and

during this time, there is refilling of the atria that causes the opening of the AV valves.

- The pressure in the aorta continues to reduce as the blood flows towards the tissues.

1. Left atrial pressure

28

2. Left ventricular pressure

3. Aortic pressure

4. Bicuspid valve closes

5. Left semi-lunar valve opens

6. Left semi-lunar valve closes

7. Bicuspid valve opens.

Question

The following graph shows pressure changes in the left part of the heart

1. Identify what the letters stand for;

a – left atrial pressure

b – left ventricular pressure

c- Bicuspid valve closes

d- Aortic pressure

e- Aortic semi-lunar valve opens

f – Aortic semi-lunar valve closes

g – Bicuspid valve opens

a) Calculate the heart rate from this graph;

N.B.

Identify two repeating points and calculate the difference to get the time for I heart beat.

1 beat = 0.6 second

x – 60 seconds

x = 100 beats /minute

b) During cardiac cycle, the pressure in the right ventricle rises to a maximum of about 3.3 kPa as opposed to

15 kPa in the left ventricle. Describe and explain this difference.

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Left ventricle has thicker muscles than right ventricle and so contract more powerfully to generate

more pressure unlike the right ventricle.

The pressure in the left ventricle is to pump blood to all parts of the body, to overcome the effects

of elastic recoil and to overcome the combined resistance of multiple capillary networks. The low

pressure in the right ventricle is to ensure there is enough time for the blood to absorb O 2 and to

remove CO2,to prevent the bursting of lung capillaries and prevent ultra filtration.

c) Immediately after the ventricular systole, which ventricle has higher pressure? And why?

Right ventricle;

This is because it has relatively thinner muscles than the left ventricle and therefore does not pump

out all the blood leading to relatively more pressure.

Pressure changes in the blood vessels

1. Pressure in the arteries

The pressure of blood in the arteries varies with the heart beat i.e. when the heart contracts, the blood pressure

increases and when the heart relaxes and refills, the blood pressure in the arteries decreases. In the arteries, there is a

high pressure because of the following reasons.

a) Little peripheral resistance due to relatively wider lumen.

Peripheral resistance is the friction between the blood and the inner smooth surface of the blood

vessels and its role is to slow down the flow of blood.

b) The pulsing of the heart is high.

2. Pressure in the arterioles

The pressure gradually decreases due to:

a) Increased peripheral resistance due to narrower blood vessels.

b) The artery divides into more arterioles, reducing the pressure.

3. Pressure in the capillaries

Pressure decreases due to;

30

a) Increased peripheral resistance due to very narrow blood vessels.

b) Reduced pulsing of the heart as these capillaries are far away from the heart.

c) Loss of substances into the tissues due to ultra-filtration.

d) Formation of many capillaries (capillary network) that reduces the pressure.

Questions

1. Describe why the blood pressure in the capillaries does not increase even though they are very narrow?

This is because they form many capillaries which together have greater total cross section area than that of the main

artery and so the pressure is shared by these many capillaries hence reducing the pressure.

2. What is the importance of low blood pressure in the capillaries?

It gives enough time for the exchange of materials through diffusion with the tissues.

To prevent bursting of capillaries

3. What are the adaptations of capillaries to exchange of substances?

The wall is one cell thick to reduce diffusion distance

They have pores to allow for the exchange of substances

They form capillary network to increase the SA of exchange.

No collagen fibers , smooth muscles and elastic fibres

4. What controls the pressure of blood in the arteries?

a) Contraction and relaxation of the heart. Contraction increases pressure in the arteries and relaxation decreases

pressure.

b) Atherosclerosis. It can permanently change the arteries by narrowing them and cause permanent rise in pressure

which can lead to cardiovascular diseases.

c) Thrombosis

5. What is the disadvantage of elastic recoil in the artery? And how does the heart overcomes this.

Elastic recoil is the shrinking of the artery when elastic fibres slacken/loosen due to the relaxation of the heart. This

can lead to the backflow of blood. However, due to powerful contraction of the large muscular left ventricle, more

pressure is generated which overcomes elastic recoil.

6. Briefly describe blood pressure measurements

- Blood pressure is measured in millimeters of mercury (mmHg)

- Blood pressure is measured using an apparatus called sphygmomanometer

- Systolic reading of a 120mmHg and a diastolic reading of 80mmHg i.e. 120/80 is regarded as normal

- Systolic blood pressure is when the ventricles contract powerfully while diastolic blood pressure is when the ventricles

relax.

- A sustained value of over 140/90 is called hypertension. This damages arteries.

- A sustained value of 90/60 or low is called hypotension. A weakened heart will produce hypotension.

NB

- The systolic pressure is the maximum pressure when the heart/ventricles contracts;120mmHg- The diastolic pressure is the minimum pressure when the heart relaxes; 80mmHg- The two are measured using sphygmomanometer.

BLOOD VESSELS

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Mammals such as humans have closed circulatory system. This means that blood flows in vessels. These

vessels are;

1. Arteries

2. Veins

3. Capillaries

Some organisms such as insects have open circulatory system. The heart of the insect is a long tube. It

pumps blood into the body cavity so that blood surrounds the cells. The blood then passes back into the

heart from the body cavity. The insect does not need blood vessels to transport blood around the body

because;

1. Insects have large surface area to volume ratio and so diffusion of blood is enough to exchange materials.

2. The cells are in contact with the blood.

3. The heart and blood are close together hence movement of blood back to the heart is fast

4. Low metabolism (chemical reactions in a cell) in insects and therefore only need diffusion of blood to get

the requirements.

The blood vessels, structures and their functional significance

32

When the above leg muscle contracts valve J closes to prevent back flow of blood in the vein. Valve k opens due

to increased pressure of blood.

Vessel Structure Functional significance

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1. Artery Tunica adventitia – collagen fibres &

some elastic fibres.

Collagen fibres provide strength so that

arteries withstand high pressure of blood

without bursting. In addition, they prevent

overstretching of arteries.

Tunica media

a) Smooth muscles

b) Elastic fibres

c) Some collagen fibres

They contract and relax to alter the

diameter of lumen to regulate blood flow.

They stretch and recoil the arteries to

maintain pressure of blood or smoothen

blood flow.

For strength

Tunica intima (endothelium) – smooth,

single layer of cells (squamous

epithelium).

It reduces friction between the walls and

the blood to ease blood flow

Narrow lumen To maintain high pressure of blood.

2. Vein Tunica adventitia – thinner collagen

fibres

Blood is under low pressure hence vessels

cannot burst.

Tunica media

a) Very little smooth muscle

b) Very little elastic fibres

No pulse of blood so no alteration of the

diameter of the lumen

No pulse of blood hence no stretching

and recoiling of veins

Tunica intima – (endothelium) –

smooth, single layer of cells-squamous

epithelium.

Reduces friction between the wall and

blood to ease blood flow

Wide lumen It acts as a blood reservoir to

accommodate large volume of blood due

to low blood pressure

Valves To stop the back flow of blood as it is

under low pressure

3. Capillaries Very thin wall (1 cell thick) Allows rapid exchange of substances between

blood and tissues i.e. reduces diffusion

distance

Pores Allows exchange of substances

Capillary network/bed Increases surface area of exchange of

substances

No valves Narrow lumen

No collagen fibres

No smooth muscles and

No elastic fibres

So that they can easily fit between cells

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Structural differences between veins and capillaries

Veins Capillaries

1. 3 layers

2. Valves

3. No pores

4. Wider lumen

5. Have collagen fibres, elastic fibres and

smooth muscles

1 layer

No valves

Pores

Narrower lumen

None

Structural differences between arteries and capillaries

Veins Capillaries

1. 3 layers

2. No pores

3. Collagen fibres, elastic fibre and

smooth muscles

1 layer

Pores

None

Structural differences between arteries and veins

Arteries Veins

1. Thick walls

2. Small lumen

3. No series of valves

4. Deeply seated

Thin walls

Wide lumen

Have series of valves

Shallowly seated

Functional differences between arteries and veins

Arteries Veins

1. Carry blood away from the heart Carry blood to the heart

2. Except for pulmonary artery and

umbilical cord artery, they carry

oxygenated blood

Except for pulmonary vein and umbilical cord

vein, they carry deoxygenated blood

3. They carry blood under high pressure They carry blood under low pressure

4. Blood flows in pulses Blood flows smoothly.

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Describe how the blood moves in veins from the body back to the heart

1. Series of semi-lunar valves that prevent back flow of blood.

2. Contraction of skeletal muscles so that they push on veins for blood to move forward.

3. Breathing in (inhalation/inspiration)- this reduces pressure in the thoracic cavity forcing the blood to move

towards it.

4. Diastole- this cause reduced pressure in the heart and the blood moves towards it.

Questions on Transport

1) Jan 09 q5

2) Jun 09 q3

3) Jan 2010 q4

4) Jun 2010 q2

5) Jan 2011 q2 & q4

6) Jun 2012 q3

7) Jan 2013 q1, q5a (i), (ii)

8) Jun 2013 q4 (c)

9) Jun 2013R q1b, q5b (ii)

10) Jan 2014 q2 & q4b

36

PLATELETS AND THE BLOOD CLOTTING PROCESS

Platelets

- Platelets are also called thrombocytes.

- They are tiny fragments of large cells called megakaryocytes which are found in the bone marrow.

- There are about 150,000 to 400,000 platelets per 1mm3 of blood.

- The role of platelets is blood clotting process.

- Their life span is 5 to 9 days.

- Platelets have no nucleus but they contain a clotting factor (enzyme) called thromboplastin.

BLOOD CLOTTING

There are 2 types of blood clots;

1. Life saving clot - in the skin

2. Life threatening clot – in the blood vessel

Blood clotting in the skin (life saving clot)

This is a vital defense mechanism for the body because when one suffers a cut or graze, the role of clotting

is to;

(i) Minimize blood loss

(ii) Prevent entry of pathogens

(iii) Provide a framework for repair.

Process of blood clotting in the blood vessel (Life threatening clot)

- This is a cascade of events leading to blood clotting.

- Blood clotting process is stimulated when there is damage to a blood vessel.

- Damage causes collagen fibres to be exposed in the vessel.

- Platelets rapidly stick to the exposed collagen fibres and these platelets release a clotting factor called

thromboplastin (enzyme) that starts the cascade.

- In the presence of calcium ions and vitamin K, thromboplastin catalyses the conversion of prothombin

(inactive plasma protein) to an enzyme called thrombin (an active plasma protein).

- Thrombin (enzyme) catalyses the conversion of fibrinogen (soluble plasma protein) into fibrin (insoluble

plasma protein).

- Fibrin forms a mesh that traps blood cells and platelets to form a blood clot.

NB.

A cascade effect is a sequence of events in which each event produces the circumstances necessary for the initiation

of the next event.

37

Suggest two differences between fibrinogen and fibrin.

Fibrinogen is globular (spherical) and fibrin is fibrous (long). Fibrinogen is soluble and fibrin is insoluble They are of different sizes

Summary of blood clotting process

A: Platelets stick to exposed collagen fibres in the damaged wall of artery

B: Thromboplastin is released

C: Vitamin K

D: Calcium ions

E: Prothrombin

F: Thrombin

G: Fibrinogen

H: Fibrin

I: Blood clot

Q1. List the factors that must be present in order for a blood clot to form;

1. Thromboplastin

2. Vitamin K

3. Calcium ions

4. Thrombin

5. Fibrin

Q2. When platelets stick to the collagen fibres in the damaged wall, the platelets break open to release several

substances of which 2 are very important. Which are these two substances and what are their roles?

1. Thromboplastin – an enzyme which initiates cascade of events in the formation of a clot

2. Serotonin- causes the smooth muscle of the blood vessel to contact. This narrows the blood vessel to

cut off the blood flow to the damaged area.

38

Cardiovascular diseases (CVDs)

- These are the diseases of the heart (cardio) and blood vessels (vascular) as a result of damage to arteries. The

damage is due to plaque formation in the arteries through atherosclerosis and clot formation in the arteries

through thrombosis, causing blockage or narrowing of arteries.

Atherosclerosis

- Athero means artery

- Sclerosis means hardening

- This is a disease of the arteries where they harden due to atheroma (fatty deposits mainly cholesterol) in the

walls of arteries. Atheroma then hardens due to accumulation of calcium salts and fibrous tissue to form a

plaque.

- Formation of atheroma on the endothelial lining (tunica intima) is because of the damage of this endothelial

lining. This damage is caused by;

1. High blood pressure (hypertension 140/90)

2. Toxins in the tobacco smoke (carbon monoxide and nicotine)

- Atheroma is the fatty deposits mainly cholesterol on the endothelial lining of arteries. When it hardens due to

accumulation of calcium salts and fibrous tissues it forms a plaque.

Immediate consequences of atherosclerosis (Plaque formation).

1. Clot formation

2. Narrowing of the artery

3. Loss of elasticity in the artery

The above three immediate consequences of atherosclerosis cause High blood

pressure.

How atherosclerosis develops

1. Damage to the endothelial lining due to high blood pressure and toxins in tobacco smoke.

2. Inflammatory response – this is increased flow of blood to the damaged area to bring in a lot of white blood cells.

3. The white blood cells cause cholesterol to build up in the damaged area to form atheroma.

4. Plaque formation – calcium salts and fibrous tissue accumulate hardening the atheroma to form a hard and uneven

swelling called a plaque on the inner wall of the artery.

5. Raised blood pressure – this is due to formation of plaque, formation of clot on the plaque, loss of elasticity of

artery and narrowing of the lumen of the artery.

6. Self-perpetuating (Positive feedback mechanism) - the formation of plaque through atherosclerosis is a self

perpetuating process (positive feedback). This is because plaque raises blood pressure and this raised blood pressure

causes endothelial damage and the damaged endothelium cause the formation of plaque that further raises blood

pressure hence causing CVDs.

39

40

Damage to endothelial lining due to HBP and toxins from tobacco smoke

Raised blood pressure Inflammatory response (WBCs move into the damaged site)

Narrowing of artery

Atheroma formation due to a building up of cholesterol

Plaque formation due to build up of calcium salts and fibrous tissue

41

CVD

Peripheral Vascular Disease (PVD) Coronary Heart Disease (CHD)Stroke (Cerebral infarction)(Cerebral infarction)

Arrhythmias Heart failureHeart attack (Myocardial infarction) Angina Pectoris

Smallest Heart AttackMedium Heart AttackLargest Heart attack (Cardiac arrest)

Ischemic Hemorrhagic Transient Ischemic

FORMS OF CVDS

1. Coronary heart disease (CHD)

- Disease that affects a pair of coronary arteries which supply the heart muscle with the glucose and oxygen

needed for respiration.

- When one of these arteries becomes blocked, the area of the heart muscle that it supplies is cut off from

oxygen and glucose and it dies giving rise to heart attack or myocardial infarction.

- When one of these arteries is partially blocked, it leads to angina pectoris.

- The two main reasons why blockages occur in the coronary arteries are:

a) Atherosclerosis – formation of plaque

b) Thrombosis – formation of clot that is usually formed on the rough surface of plaque

- So, there are two main forms of CHD (coronary heart disease);

a) Heart attack – due to blockage of a coronary artery.

b) Angina pectoris – due to partial blockage of a coronary artery.

Other forms of CHD

- Overtime, CHD can weaken the heart muscle and lead to;

(i) Heart failure – condition in which the heart cannot pump enough blood to meet the body’s

requirements.

(ii) Arrhythmias- irregular heartbeat.

2. Stroke (cerebral infarction)

- Supply of oxygenated blood to part of the brain is cut off causing its death.

3. Peripheral vascular disease (PVD)

- This is due to blockage/narrowing of arteries leading to periphery especially in the legs. This leads to tissue

death and then tissue decay (gangrene).

42

Thrombosis (clot formation)

There are two ways of forming a clot;

1. Through atherosclerosis i.e. a clot is formed on a rough surface of a plaque to block the artery.

2. Direct formation of a clot – platelets come into contact with damaged endothelium and trigger clot

formation.

Types of clots in the arteries

1. Thrombus – does not move along with blood hence it is stationary.

2. Embolus – carried by the blood from the origin to elsewhere to cause blockage or narrowing of the artery.

Aneurysm

- This is the weakening of the wall of an artery which produces a balloon like blood filled swelling formed

behind a plaque with a clot on its surface.

- Aneurysm (balloon like blood filled swellings) frequently burst leading to hemorrhage and therefore loss of

blood to the region of the body served by that artery.

- A brain aneurysm is known as cerebrovascular accident (CVA) or stroke.

Heart attack (myocardial infarction)

- This is a sudden and severe chest pain due to the death of part of the heart muscle.

- The death is due to lack of oxygen in these heart muscles as a result of blockage of coronary artery by clot or

plaque

- There are 3 forms of heart attack;

1. Largest heart attack (cardiac arrest). It occurs if blockage happens in one of the coronary arteries (Right or

left) before it branches so that a large area of heart muscle dies.

2. Medium heart attack – blockage is in one of the branches of the right or left coronary artery.

3. Smallest heart attack – blockage is in the further branched blood vessels causing the death of a small tissue

of the heart.

The two major factors that can cause death as a result of heart attack are;

1. Cardiac arrest

2. If medical attention is delayed.

The symptoms of the heart attack are;

1. Shortness of breath

2. Angina pectoris

3. Arrhythmia – the heart beats irregularly

4. Fatigue

5. Indigestion

43

The two major steps to be taken when you suspect someone is developing or having a heart attack are;

1. Give them 2 full strength aspirin tablets to stop blood clotting i.e. the aspirin bursts the clot

2. Call an ambulance.

Question

The plaque often increases in size and can block the artery. If the artery supplying blood to the

heart becomes blocked, blood no longer flows to the heart muscle cells. Shortly after the loss of

blood flow, heart muscle cells stop contracting and start to die. In the heart muscle cells,

energy (ATP) is made available from respiration. The graph below shows how the energy (ATP)

available to heart muscle cells changes with time, after the loss of blood flow.

(i) Using the information in the graph, describe how the energy (ATP) available to the heart muscle cells

changes with time after the loss of blood flow.(2)

decrease in ATP with time

drop in the fall of ATP gets less with time

manipulation of figures e.g. from 0 to 80 minutes the ATP dropped by 100

(ii) Suggest why there are changes to the available energy (ATP) in the heart muscle cells following the

loss of blood flow.(2)

less oxygen available

less respiratory substrate/ glucose

less aerobic respiration

(iii) About 8 minutes after the loss of blood flow, the heart muscle cells no longer contract. After about

20 minutes, the heart muscle cells begin to die. Using the information in the graph and your own

knowledge, suggest explanations for the timings of these two events. (3)

due to anaerobic respiration in the heart muscle, lactic acid builds up which inhibits respiratory

enzymes reducing respiration hence reducing ATP production. So at 8 minutes there is

insufficient ATP for contraction ;

after 20 minutes the ATP levels are too low to sustain cell survival ;

44

(iv) If blood flow is restored within 30 minutes, most heart muscle cells will eventually recover. Suggest

an explanation for this recovery. (2)

restored blood flow provides muscle cells with oxygen and removes lactic acid

aerobic respiration restarts and produces more ATP for muscle contraction.

(Total for Question 5 = 12 marks)

Angina pectoris

- This is a severe chest pain that is usually experienced during vigorous exercise (exertion) as a result of

narrowing of coronary arteries.

- The pain starts when exercising but stops when the exercise stops.

- The pain is due to lactic acid produced during anaerobic respiration in the heart muscle.

- Anaerobic respiration is due to shortage of oxygenated blood as a result of narrowing of a coronary artery.

- It does not cause death of heart muscle.

- It is a strong symptom for a heart attack.

- The symptoms of Angina pectoris are;

1. Severe chest pain that extends to the left arm, shoulder and jaw.

2. Shortness of breath.

The following factors prevent Angina pectoris;

1. Low fat diet.

2. Regular exercise.

3. Losing weight.

4. Stop smoking.

The symptoms of angina pectoris can be treated as follows;

1. Medical drugs to dilate coronary arteries for sufficient oxygen supply to the heart muscle.

If the condition is serious, a heart bypass surgery (Coronary artery by-pass operation) Insertion of a coronary stent Heart transplant Angioplasty

Angioplasty is the technique of mechanically widening narrowed or obstructed arteries. A coronary stent is a tube placed in the coronary arteries that supply the heart, to keep the arteries

open in the treatment of coronary heart disease.

Stroke (cerebral infarction)

- This is the death of the part of brain tissue caused by bursting (Hemorrhagic) or blockage (Ischemic) of an artery that supplies the brain with oxygenated blood.

- Usually the blockage of an artery is by a blood clot formed by atherosclerosis (a clot on top a plaque).

45

- If the blockage affects one of the main arteries leading to the brain, a very serious stroke occurs that may lead

to death. However, if blockage affects smaller arterioles leading to the brain, the effect may be less severe.

- The symptoms of stroke appear very fast and the damage happens very quickly.

- The symptoms of stroke include;

(i) Numbness

(ii) Dizziness

(iii) Confusion

(iv) Slurred speech

(v) Loss of vision usually in one eye

(vi) Paralysis of one side of the body with a drooping hand, leg or eyelid or dribbling mouth.

- The quick treatment for stroke that may help the patient to survive is giving clot bursting drugs such as

aspirin.

46

Risk factors for cardiovascular disease (CVD)

- Risk is the probability of the occurrence of an unwanted event or outcome.

- There are two types of risks;

1. Perceived risk

2. Actual risk

Perceived risk

- A risk that is ‘thought of’ and can be underestimated or overestimated.

- People will overestimate the perceived risk if the risk is;

a) Impose sudden changes where the consequences are severe.

b) Involuntary (not under our control)

c) Not natural

d) Unfamiliar

e) Dreaded.

- A lot is known about the effect of diet, exercise and smoking on the risk of CVD. But many people do not

change their lifestyle due to perception of risk. This perception of risk is affected by;

a) Own experience

b) Inability to assess risks well

c) Peer pressure

d) Fatalistic ideology (what is destined to happen must happen).

e) Remoteness of the likely consequences.

Actual risk;

- This is what actually happens;

- The factors that increase the actual risk of suffering from CVDs are;

a) Genetic

b) Gender

c) Age

d) Diet

e) High blood pressure

f) Smoking

g) Inactivity

h) Obesity

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The above factors can be divided into three.

1. The ones that can be altered because they are lifestyle factors. These include

a) Diet

b) Smoking

c) High blood pressure

d) Inactivity

e) Obesity

2. Factors that can’t be altered and they include;

a) Genetic

b) gender

c) age

3. Factors that have lifestyle and genetic components.

High blood cholesterol

High blood pressure

Obesity

Diabetes

- A lifestyle factor is the one that is affected by the way we live e.g. physical inactivity and smoking are lifestyle

factors as we choose to live this way.

Risks factors for CVDs that cannot be altered

1. Genetic

- Due to inheritance some people have;

a) Tendency to high blood pressure.

b) Tendency to poor cholesterol metabolism.

c) Arteries that are more easily damaged.

d) Mutation in genes that affect relative HDL to LDL levels.

- Risk factors with genetic components are;

a) high blood pressure

b) high blood cholesterol

c) obesity

d) diabetes mellitus

2 Gender

- Oestrogen gives women some protection from CVDs before menopause. After menopause the risk in both

sexes is about the same.

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3. Age

- Elasticity and width of arteries decrease with age. This raises blood pressure which is a risk factor of

CVDs.

Risk factors of CVDs that can be altered: lifestyle factors.

1. Diet

- Many correlations (links) between dietary habits and the level of CVD have been investigated e.g.

saturated fat, cholesterol and lipoprotein levels. Some evidence that these correlations are causal have been

documented.

- Correlation – when one variable changes there is also a change in an accompanying variable.

- Causation –change in one variable is responsible (it causes) for the change in the other variable.

- Our choices of food can increase or decrease the risk of developing CVDs.

- Risk for CVDs increases with high intake of;

a) Saturated fat such as animal fats

b) High salt intake

- Risks for CVDs decreases with;

a) High intake of antioxidants e.g. vitamin C and E found mostly in fruits and vegetables. Another antioxidant

that needs moderate and regular intake is wine especially red wine.

b) High intake of soluble fibre

c) Moderate intake of unsaturated triglycerides mainly from fish and vegetables.

Cholesterol

- Cholesterol is insoluble in water and thus is transported in blood plasma as lipoproteins.

- Cholesterol is essential for good health for the following reasons;

a) Synthesis of vitamin D in the skin

b) Synthesis of steroid hormones such as progesterone and testosterone

c) Synthesis of plasma proteins

d) Synthesis of bile salts

e) Synthesis of some growth hormones

f) Synthesis of cell membranes to control fluidity of these membranes and give strength to them.

- There are 2 sources of cholesterol

a) Liver

b) Diet – associated with saturated fats such as eggs, meat and dairy products.

Note: High blood cholesterol can be inheritable

- Health problems arise when there is excess cholesterol that has accumulated in tissues.

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- Excess cholesterol in blood build up on artery wall forming atheroma that hardens (due to build up of calcium salts and fibrous tissue) to form plaque. This is atherosclerosis. The subsequent consequences of atherosclerosis include; narrowing of arteries, clot formation and loss of elasticity of arteries. All these lead to CVDs.

- There are three types of cholesterol (lipoproteins);

1. Low density lipoproteins (LDL)

2. High density lipoproteins (HDL)

3. Very low density lipoproteins (VLDL)

Note:

- Good and bad cholesterol are not different to each other chemically, it is the way the cholesterol is carried in the

blood that is different.

- Low density lipoproteins are formed from saturated fats, proteins and cholesterol. They bind to LDL receptors

on the surface of the cell, saturating them so that LDLs remain in the blood instead of being absorbed by

the cells and this raises blood cholesterol level. It is associated with the development of atherosclerosis and

therefore it should be maintained at low levels.

- High density lipoproteins are formed from unsaturated fats, proteins and cholesterol. They transport

cholesterol from the body tissue including artery walls to the liver where it is broken down and excreted. It

reduces blood cholesterol level hence discourages atherosclerosis and therefore should be maintained at high

levels.

Note:

Cholesterol is not saturated fat but is made in the liver from saturated fats absorbed from food.

Low density lipoproteins (LDLs)- bad

cholesterol

High density lipoproteins (HDLs)- good

cholesterol

Formed from saturated fats, proteins and

cholesterol

Formed from unsaturated fats, proteins and

cholesterol

They bind to the LDL receptors on the cell

surface membrane, which can become

saturated leaving the LDLs in the blood.

They transport cholesterol from the body

tissues to the liver where it is broken down and

excreted.

Associated with development of

atherosclerosis as it is in large amounts and

remains in the blood.

Reduces blood cholesterol levels hence

discourages atherosclerosis.

Should be maintained at low levels. Should be maintained at high levels.

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Questions

1. What is the difference in density of proteins between LDLs and HDLs

LDL has low density of proteins and more cholesterol whereas HLD has high density of

protein and less cholesterol.

2. The role of HDL is to transport cholesterol from the body tissues to the liver to be broken down and

excreted. What is the advantage of this?

i. It lowers blood cholesterol levels, hence reduces formation of atheroma.

ii. It helps remove the fatty plaques of atherosclerosis hence reduces CVDs.

3. Describe the role of monounsaturated triglycerides in reducing blood cholesterol?

They help in the removal of LDLs from the blood and transport them to the liver where they are

broken down and excreted. They include olive oil and peanut oil.

4. Describe the role of polyunsaturated triglycerides in the reduction of blood cholesterol?

They increase the activity of the LDL receptors on the surface of cells so that LDLs are actively

removed from the blood and enter these cells. They include vegetable oils, fish oil and sunflower

oil.

5. Total fat has both saturated fats and unsaturated fats. Comment on the effects it has on health.

Saturated fat can be made into cholesterol that becomes part of LDL, increasing the risk of CVD,

while unsaturated fat becomes part of HDL and reduces risk of CVD.

6. What is the major disadvantage of high blood cholesterol?

It increases the chance of atherosclerosis that causes CVDs because the cholesterol forms

atheroma that then hardness to form plaque.

2. Smoking - Tobacco smoke has several components that are risk factors for CVDs. These include:

a) Carbon monoxide1. Increases the levels of low density lipoproteins and lower high density lipoproteins (the good type of cholesterol). 2. Permanently binds to hemoglobin depriving the tissues of oxygen.

b) Nicotine

(i) Vasoconstriction It causes constriction of the blood vessels hence reducing blood flow to the heart and increasing blood pressure.

Nicotine is able to do this by binding to proteins called nicotinic receptors. When nicotine binds to these proteins, it signals for the smooth muscle around the blood vessels to contract, which makes the blood vessels narrower. This can contribute to heart disease in two ways--by reducing blood flow to the heart and by increasing blood pressure. Constricted coronary arteries reduce the amount of blood that gets to the heart. Constricted arteries throughout the body increase the blood pressure, which forces the heart to work harder. The added strain on the heart can lead to heart disease.

(ii) Endothelial Damage Causes damage to the lining of blood vessels increasing chances of atherosclerosis.

Elevated levels of nicotine are correlated with inflammation and damage of endothelial cells in blood vessels. Endothelial cells line blood vessels throughout the body.

(iii) Release of Adrenaline that increases heart rate When nicotine is in the brain, it causes the release of adrenaline that causes heart's rate to increase, leading to higher blood pressure

which also limits blood flow to the heart.

(iv) Makes platelets ‘sticky’ increasing the chances of blood clotting.

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3. Alcohol Alcohol and the Cardiovascular System

Heavy drinking raises levels of triglycerides circulating in the bloodstream, which are a type of cholesterol that lead to diabetes and also block or narrow down arteries that carry blood to the heart. If coronary arteries are clogged with fats, blood cannot flow freely, resulting in heart disease or stroke.

Alcohol directly contributes to heart failure by damaging the heart muscle and arteries. Cardiomyopathy, or an enlargement of the heart muscle, results from long-term alcohol use. An enlarged heart no longer works

efficiently and fails to provide enough oxygenated blood to other organs of the body. Furthermore, alcohol is associated with cardiac arrhythmia (irregular heartbeat), sudden cardiac death and stroke. Binge drinking increases the risk of atrial fibrillation, or an ineffective quivering of the heart instead of an actual beat.

NB Two drinks a day for men younger than age 65 One drink a day for men age 65 and older One drink a day for women of any age

A drink is 12 ounces (355 milliliters) of beer, 5 ounces (148 milliliters) of wine or 1.5 ounces (44 milliliters) of 80-proof distilled spirits. ORModerate and regular drinking of alcohol (2-3 units per day for women and 3-4 units per day for men) may decrease risk of CVDs. 1 unit = 8g of alcohol. Large glasses of wine in pubs, restaurants and wine bars contain 2-3 units of alcohol, and thus women should take 1 glass and men should take 2 glasses.

- In the liver, alcohol is converted into ethanal (3 carbon carbohydrate). Most of the ethanal is used in respiration but some may end up in very low density lipoproteins increasing the risk of plaque formation (atherosclerosis).

4. Exercise

- Risk of CVDs decreases with more exercise. Exercise helps to control:-

a) Blood cholesterol by raising HDL cholesterol without affecting LDL cholesterol.

b) Blood pressure – exercise dilates blood vessels hence lowers blood pressure.

c) Diabetes mellitus due to increased respiration that reduces blood glucose.

d) Obesity due to increased respiration that reduces blood glucose.

- Moderate exercise that reduces risk include;

a) Walking

b) Cycling

c) Swimming

5. High blood pressure

This is also called hypertension.

It damages endothelial lining of arteries causing atherosclerosis that lead to CVDs

Risk increased with increase in blood pressure.

The causes of hypertension are:-

a) Genetical (inheritance)

b) Age – increased with age

c) High blood cholesterol levels

d) High alcohol intake

e) Smoking – can cause production of Adrenaline

f) High salt intake

g) Stress – can cause production of Adrenaline

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BENEFITS AND RISKS OF TREATMENTS OF CVDS

HIGH BLOOD PRESSURE

High blood pressure (hypertension) is one of the main risk factors for the later development of heart disease.

Narrow blood vessels are often the cause of high blood pressure. When blood vessels are too narrow, the heart must work extraordinarily hard to pump blood throughout the body.

Blood vessels often become more narrow when they're affected by angiotensin-converting enzymes (ACE) released by the body. These enzymes trigger the blood vessels to constrict and tighten. This enzyme can be subdued by ACE inhibitor medication.

TREATMENT OF HIGH BLOOD PRESSURE

- There are 5 main types of drugs that are used to treat high blood pressure.

- These drugs are called antihypertensive drugs.

- These drugs are:-

Angiotensin converting enzyme inhibitors (ACE inhibitors)

ACE inhibitors are antihypertensive drugs which reduce the synthesis of Angiotensin II from angiotensin I.

Angiotensin is a hormone that is produced in inactive form called Angiotensin I.

An enzyme converts Angiotensin I into an active hormone called Angiotensin II.

Angiotensin II causes vasoconstriction of blood vessels raising blood pressure.

The ACE inhibitors are antihypertensive that inhibit the enzyme so that Angiotensin I is not activated,

lowering the blood pressure.

To explain how ACE inhibitors: ACE inhibitors have similar shape to Angiotensin I hence fit in the active

site of the ACE acting as an active site directed inhibitor so that there is no conversion of Angiotensin I to

Angiotensin II.

The side effects of ACE inhibitors are:-

a) Dry cough

b) Dizziness due to rapid lowering of blood pressure

c) Abnormal heart beats (Arrhythmia)

d) Reduction in functioning of the kidney (impaired kidney function)

Question

Describe and explain how ACE inhibitors work.

This is an anti-hypertensive drug. They inhibit the enzyme called Angiotensin Converting Enzyme (ACE) from activating a hormone called

Angiotensin I into Angiotensin II. Angiotensin II hormone constricts the arteries, raising the blood pressure.

They have similar shape to Angiotensin I (substrate) so that they bind to the active site of the ACE so that no synthesis of Angiotensin II and the blood vessels remain dilated; hence reducing blood pressure.

This anti-hypertensive acts as Active Site Directed Inhibitors.

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Calcium channel blockers

These are antihypertensive drugs that block the calcium channels in the muscles in the lining of the

arteries, to prevent contraction of the muscle so that the blood vessels do not constrict and this lowers

blood pressure.

Note

The muscles are mainly found in the Tunica media

The side effects include:-

a) Dizziness due to rapid lowering of blood pressure

b) Swelling of ankles due to buildup of fluids in the legs

c) Abnormal heart rhythms

d) Flushing red in the face

e) Constipation

NB.

People with heart failure taking some calcium channel blockers can worsen symptoms of being fatal. This is because

the heart muscle will not contract as required due to lack of calcium ions.

Unlike other drugs used to treat high blood pressure, calcium channel blockers are generally not given to people who have heart failure or actual physical damage to the heart muscle.

To explain how calcium channel blockers work: Calcium channel blockers attach to the target of a specific chemical signal and preventing the signal from reaching and activating that target. So, calcium is prevented from entering muscle cells, which, in turn, decreases the amount of force the muscle can generate when contracting.

The specific targets blocked by calcium channel blockers exist in high numbers both on blood vessels and in the heart, allowing the drug to exert most of its influence in these areas

Diuretics

They are anti-hypertensive drugs that increase the volume of urine produced by the kidneys and therefore

lowers the excess fluids and salts in the body, hence lowers the blood pressure.

Diuretics cause your body to produce more urine. Urine flushes excess water and sodium out of your body. This lowers blood pressure because the more you

urinate, the lower the volume of fluid in your bloodstream. Less fluid in your bloodstream means there is also lower pressure on your artery walls. In addition, the loss of excess sodium causes your blood vessels to open wider. This causes further lowering of your blood pressure.

The side effects include:-

a) Dizziness due to rapid lowering of blood pressure

b) Nausea

c) Muscle cramps

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Beta blockers

These are anti hypertensive drugs that interfere with the normal system of controlling the heart. They ensure that

the heart does not respond to hormones that speed up the heart beat e.g adrenaline and therefore lowers the blood

pressure.

The side effects include:-

Dizziness due to rapid lowering of blood pressure

A beta blocker is a medication that slows the heart rate and reduces the force with which the heart muscle contracts, thereby

lowering blood pressure. Beta blockers do this by blocking beta-adrenergic receptors, preventing adrenaline (epinephrine)

from stimulating these receptors.

Beta blockers can be described as either “selective” or “nonselective” and “vasodilating” or “nonvasodilating.”

Selective beta blockers work by blocking the effect of adrenaline in the heart, but not in the lungs or elsewhere in the body.

Beta blockers that vasodilate have the effect of relaxing and widening the blood vessels, allowing blood to flow more easily

through your arteries. This means the heart doesn't have to pump as hard and blood pressure is reduced.3

Question

Describe and explain how beta-blockers function.

This is an anti-hypertensive drug. They reduce blood pressure by preventing the heart from responding to adrenaline hormone. Beta blockers have similar shape to adrenaline, so, they bind to adrenaline receptors on the CSM on the

heart muscle cells. So, adrenaline does not bind hence no increase in heart rate and this causes decrease in blood pressure.

Sympathetic nerve inhibitors/Vasodilators

- Vasodilators are anti-hypertensives that act directly on smooth muscles in blood vessel walls to make blood vessels widen (dilate).

- By widening the arteries, these drugs allow blood to flow through more easily, reducing blood pressure. - So, your heart doesn't have to pump as hard and your blood pressure is reduced.

Question

Describe and explain how vasodilators (sympathetic nerve inhibitors) reduce blood pressure.

They prevent the muscle fibres in the Tunica media of arteries from responding to the nerve impulse hence no contraction and therefore no constriction so that the arteries remain dilated, reducing blood pressure.

TREATMENT OF HIGH BLOOD CHOLESTEROL LEVELS BY CHOLESTEROL LOWERING

DRUGS.

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The main types used are plant statins

Plant statins are a group of drugs that lower blood cholesterol

Hydroxymethylglutaryl-coenzyme A (HMG-CoA) is the precursor for cholesterol synthesis. It binds to

the active site of the enzyme HMG-CoA reductase to form mevalonate that is later converted to

cholesterol.

How do statins work?

i) They act as active site directed inhibitors by binding to the active site of HMG-CoA reductase

hence lower blood cholesterol level.

ii) Additional enzymes in the liver cell sense that cholesterol production has decreased and respond by

creating a protein that leads to an increase in the production of LDL receptors. These receptors

relocate to the liver cell membranes and bind to passing LDL and VLDL (very low density

lipoprotein). The LDL and VLDL then enter the liver and are digested. This increase HDLs.

The above 2 functions of plant statins reduce the risk of developing atherosclerosis hence reduces risk of

CVD’s

In patients who have CV D treatment with statins they reduce the risk of heart attack by upto 33%

In people who don’t have CVD but have elevated blood cholesterol levels, statins lower total LDL

cholesterol by more than 20% and the risk of CVD’s by a similar percent

The side effects are very rare when using statins. However, the side effects include:-

a) Joint problems

b) Liver and kidneys problems

c) Gastro – intestinal problems e.g. constipation

d) Respiratory cancer

e) Reduced vitamin intake

Explain how lowering blood cholesterol levels can reduce the risk of CVD- Less cholesterol in the blood to build up on artery wall (atheroma)- Hence less likely to develop atherosclerosis- The subsequent consequence of atherosclerosis are narrowing of arteries,

ischaemia (restriction of blood flow), decrease in flow of blood to the heart, high BP, clot formation, loss of elasticity

N.B. Cholesterol: below 5 mmol/litre is the best; 5.2-6.2 bordering high risk; above 6.2 high risk.

TREATMENT OF HIGH BLOOD PRESSURE AND HIGH CHOLESTEROL LEVEL USING ANTI

COAGULANTS AND PLATELET INHIBITORY DRUGS.

This is the last treatment applied when:-

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a) Someone had a heart attack or stroke

b) Someone is identified as being at a risk of one heart attack or stroke

c) Such people are given drugs to prevent platelets aggregation and clotting in the artery

A) PLATELET AGGREGATION INHIBITORY DRUGS

1. Aspirin

Prevents platelets from aggregation by reducing stickiness of platelets hence reduces clot formation.

The side effects of using aspirin are

a) Irritates the stomach lining

b) Bleeding in the stomach

c) Some people are allergic to it.

d) Not effective in some people

e) Partially effective in some people.

2. Clopidogrel

It is an alternative platelet aggregation inhibitory drug to aspirin. The benefits may be greater than with

aspirin for some patients but the risk of bleeding is higher than with aspirin.

3. A combined treatment but has a greater risk of stomach bleeding than even when aspirin is used alone.

B) ANTI COAGULANT DRUGS SUCH AS WARFARIN

This is an anticoagulant dug that interferes with the synthesis of prothrombin hence prevents blood

clotting

It can be taken orally

OBESITY INDICATORS

- Obesity occurs when one takes more energy than required by the body. The excess energy is converted into

fat and stored in the body.

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- Obesity can be inheritable.

- The side effects of obesity are;

a) Diabetes

b) High blood pressure

c) CVDs

d) Joint problems

- There are two obesity indicators;

a) BMI (body, mass index)

b) Waist to hip ratio (WHR)

a) Body mass index (BMI)

- It is calculated as follows;

BMI=Body mass(kg)

Height∈meters squared

For example, weight of a person is 70kg and height is 1.75m

BMI = 70 = 22.9KG M

(1.75)2

- The following table gives the BMI and the corresponding status

BMI Status

<20 Under weight

20-25 Normal weight

25.1-30 Overweight

< 30 Obese

- The person, in the example, with BMI of 22.9 has the normal weight hence safe from CVD

- Use of BMI as an indicator of obesity has several disadvantages;

a) Incorrect in medical cases that lead to overweight and underweight conditions.

b) Incorrect in fitness cases where there are large muscles. The weight of large muscle will be treated as the

weight of fat by BMI.

c) Incorrect with advanced age due to reduced body mass.

b) Waist to hip ratio

The waist measurement is taken by a non-stretchable tape above the hip bone, below the rib.

The hip measurement is taken by the tape around the widest part of the buttocks.

For men, it should not be more than 0.90; otherwise it will be overweight hence risk of CVD.

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For women, it should not be more than 0.85; otherwise it will be overweight increasing the risk of CVD.

Waist to hip ratio is the best indicator of obesity compared to BMI.

Obesity and CVDs Obesity is as result of intake of extra energy that is converted to saturated fat and stored in the body.This stored fat affects the chances of getting CVDs as follows;

1) It is a source of LDL that increases blood cholesterol level which in turn increases the chances of forming atheroma during atherosclerosis.

2) The fat can be deposited on the wall of inner layer of arteries (tunica intima/endothelium), reducing the lumen and this causes HBP that is a risk factor for CVDs.

TYPES OF ENERGY IN THE BODY

1. Basal metabolic rate (BMR)

- Minimum amount of energy needed for only essential body processes per day (24 hours).

- The essential body processes are;

1. Breathing

2. Heart rate

3. Body temperature

- Measurements of BMR show that an average man needs to take about 1500kJ day-1 and an average woman

needs to take about 5850 kJ day-1. This does not reflect the activities.

- BMR varies with:-

a) Age – higher in young people

b) Gender – higher in males

c) Body mass – higher in heavier people

d) Activity – higher in active people

2. Physical activity level (PAL)

(v) In addition to BMR , energy is needed for physical activity.

(vi) PAL is a factor that reflects physical activity.

(vii) In a man with low physical activity PAL 1.4.

3. Estimated average requirements (EAR) for energy

- An individual EAR for energy is determined by multiplying the BMR by the PAL

EAR = BMR x PAL

4. Dietary reference value (DRV)

- In the UK, DRVs are estimates of the requirements of energy and aren’t recommendations for individuals.

These include:-

EAR = BMR x PAL

LRNI = low reference nutrient intake

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HRNI – high reference nutrient intake

- These estimates effectively provide a range of values within which a healthy balanced diet should fall.

Energy balance & Energy imbalance

a) Energy balance

- Energy balance is when the body’s energy requirements is equal to energy intake hence there will be no

underweight or overweight concern.

b) Energy imbalance

- Energy imbalance is when one consumes more or less energy than the body’s requirements leading to

overweight and/or obesity or underweight, respectively.

- Obesity or overweight increases the risk of CVDs due to high blood pressure, high cholesterol level,

leading to CVDs. In addition, diabetes and joint problems may set in due to obesity or overweight.

- For underweight the body is weak and can be subjected to various diseases.

Question

Martin, a mason weighs 70kg. The human basic energy requirement is 4kJkg -1 of body mass hr-1 (per hour). As a

mason, his daily energy requirement is 5000kg. His total energy intake is 10300kJday-1.

(i) Calculate the basic energy requirement per hour;

4kJ 1kg

X 70kg

= 280kJ/hr

(ii) Calculate his BMR;

280kJ 1hr

X 24hrs

= 6720kJ day-1

(iii) Calculate his total energy needed per day;

= 6720 + 5000

= 1172kJ day-1

(iv) Calculate his energy balance;

= 10300 – 11720

= -1420kJ day-1

(v) Conclusion; He loses weight.

POPULATION STUDIES IN RISK FACTORS

Epidemiology

- Epidemiologists are scientists who carry out research to determine the risk factors for health.

- There are two kinds of epidemiological studies;

a) Cohort studies

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b) Case-control studies

Cohort studies

- The main features are:-

Large number of people is observed.

It takes long period of time.

They are monitored to see if they develop the condition under study.

Those that develop the condition are put in one group, those who don’t in another group.

Various risk factors that the subjects (people) have been exposed to are looked out by interviewing

them.

Correlations and causations are identified.

The disadvantages of Cohort studies are;

1) Large number of people is observed.

2) It takes long period of time.

3) It is expensive

Case-control studies

The main features of case-control studies are:-

A group of people with the condition (case) is compared with a group that does not have (control)

Past history is then investigated to identify factors leading to one group having the disease and the other

not.

It’s very important to match the control with the case group e.g. age and gender.

A GOOD STUDY

It is the one with the following features;

Sample should be representative to avoid bias.

Sample size is large. In many diseases, only a low percentage of the population has the condition, so a large

sample may contain a small number of individuals with the condition.

Variables should be controlled when selecting cohort or control groups. This is one of the most difficult

aspects of this kind of study since human beings are so variable in terms of genes and environment.

Measurement techniques involve questionnaire in order to standardize the measurements.

NB

- In any good study, valid and reliable data should be collected.

a) Valid data – data that accurately measures what they are supposed to.

b) Reliable data – can be replicated.

Errors in lab experiments

- All experiments are subjected to errors.

- These errors could be:-

(i) Systematic errors

- Values differ from the true value by the same amount. Examples of systematic errors include;

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a) Errors due apparatus e.g. a burette or pipette have an error in its volume.

To solve this error one can add /subject a certain volume e.g. 1cm3

b) The experimenter reads the volume at the wrong place each time, so under- or over- estimating the

true volume at each time.

(ii) Random errors

- Values are lying randomly above or below a true value

- They are mainly experimenter’s errors

- Examples include;

a) The end point of a colour change is misjudged.

b) The vitamin C can’t be added by less than a drop at a time and so sometimes the next drop may be

too much and other times too little.

c) Failure to rinse beetroot disks well.

Question:

- In vitamin C experiment,

1. List the precautions to be taken when carrying out the vitamin C experiment.

2. List ways through which vitamin C is lost from food.

3. Describe how you would compare the vitamin C of 3 different vegetables.

Questions on CVDs

1) Jan 09 q1, q6 & q7

2) Jun 09 q4 & q5

3) Jan 2010 q5 & q8

4) Jun 2010 q4 & q7

5) Jan 2011 q1 & q7c

6) Jun 2011 q5 & q8

7) Jan 2012 q7 & q8

8) Jun 2012 q5 & q7

9) Jan 2013 q5b(i) (ii) & q7

10) Jun 2013 q1a , 3bi, ii, iii & q8

11) Jun 2013R 1a & q8

12) Jan 2014 q5

CELL MEMBRANES

Structures and properties of cell membranes

- There are two types of membranes of cells;

a) Those surrounding the organelles. An organelle is a minute structure in the cytoplasm that has a specific

function e.g. mitochondria and nucleus

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b) The one that forms the boundary of the cell. This is called the cell surface membrane or outer cell membrane or

plasma membrane.

Functions of the membrane surrounding the organelles;

1. Some reactions take place on the membrane surfaces e.g. part of respiration happens on the mitochondrial

membranes.

2. Hold electron carriers e.g. inner mitochondrial membrane

3. Formation of secretory vesicles by Golgi apparatus.

4. Formation of vesicles from rough endoplasmic reticulum (RER)

Functions of cell surface membrane;

1. Partially permeable to substances entering and leaving the cell.

2. Holds the cell contents together.

3. Allows endocytosis and exocytosis to take place. During endocytosis, part of the cell surface membrane

breaks and enclose the substance to be taken into the cell. During exocytosis, the substance to be secreted

out of the cell is enclosed by a vesicle (secretory vesicle) that have been pinched off from membranes of

organelles and these vesicles fuse with the cell surface membrane to release these substances out of the

cell.

Structure of the cell surface membrane

- The structure of the cell surface membrane is made up of:

1. Lipids;

(i) Phospholipids

(ii) Cholesterol

(iii) Glycolipid

2. Proteins;

(i) Extrinsic Proteins/Peripheral proteins

(ii) Extrinsic Proteins/Integral proteins

3. Carbohydrates;

(i) Glycoprotein

(ii) Glycolipid

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a) Phospholipid

b) Phospholipid bilayer

c) Glycoprotein –Integral/Intrinsic

d) Glycolipid

e) Integral protein (channel protein/ion channel) - transmembrane protein

f) Peripheral protein

g) Integral protein (embedded in one layer-outer or inner) - transmembrane protein

h) Cholesterol

i) Carrier protein (Integral protein) - transmembrane protein

Lipids in the cell surface membrane

- There are 3 types of lipids in the cell surface membrane;

a) Phospholipids

b) Cholesterol

c) Glycolipid

Phospholipids

- They are the most abundant component of the cell surface membrane.

- The structure of the phospholipid molecule consists of:

(i) 1 glycerol

(ii) 2 fatty acids

(iii) 1 phosphate group

(iv) Ester bonds that join fatty acids to glycerol.

(v) Phosphate-ester bond that joins phosphate group and glycerol

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- The polar phosphate head is hydrophilic (polar) and dissolves readily in water.

- The fatty acid tails are hydrophobic (non-polar) and are insoluble in water.

Question

Why do phospholipids form a bilayer and not a monolayer?

- The property of phospholipids (hydrophilic phosphate head and hydrophobic fatty acid tails) causes the

formation of the bilayer.

- The hydrophobic fatty acid tails face/orientate inwards (non polar environment).

- The hydrophilic phosphate heads face/orientate outwards (polar environment) i.e.in the cytoplasm and

tissue fluid.

- So, phospholipids form a bilayer.

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NB

- If the phospholipids molecules are tightly packed in water, they either form:

1. Monolayer:- with hydrophilic heads in the water and hydrophobic fatty acid tails in the air.

2. Micelles: A micelle is a structure formed by a cluster of molecules with both hydrophobic and hydrophilic

ends when placed in water. In a micelle, all the hydrophilic heads point outwards hence face the water, and

all the hydrophobic fatty acid tails point inwards (are hidden inside) i.e. non polar environment.

NB

- Phospholipid cause fluidity in the membrane while cholesterol controls fluidity..

Cholesterol

- The structure of cholesterol is:-

- In the cell surface membrane, cholesterol has 2 functions;

1. Control fluidity so that the cell membrane is not too fluid or too rigid

2. Provides mechanical strength to the cell membrane. Those that do not break easily

Glycolipids

- A Glycolipid is a phospholipid attached to carbohydrate.

- It is found only on the outer part of the phospholipid bilayer (next to the tissue fluid).

- Its functions are:-

a) Cell to cell recognition – to identify non self and self cells.

b) Cell adhesion

c) Acts as receptors

d) Acts as antigens

Protein in the cell surface membrane

- There are different types of protein in the cells. These include;

a) Peripheral protein

b) Integral protein

- All these proteins are found on and in the the cell surface membrane

a) Peripheral proteins

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- These are attached to the surface of phospholipids bilayer.

b) Integral proteins

- These are embedded in the phospholipid bilayer. They include:

1. Those embedded in the inner and outer phospholipid layers.

2. Trans-membrane proteins. They span through the phospholipid bilayer so that they are exposed at both

ends. These are:-

a)Channel proteins which are either gated or fixed proteins.

b) Carrier proteins which are globular proteins.

c)Some glycoproteins- A carbohydrate attached to a protein (same functions as glycolipid)

Roles of proteins in the cell surface membrane

1. Transport of substances

This is carried by channel and carrier proteins

2. Structure of proteins

They all give strength to the cell membrane

3. Cell to cell recognition by the glycoprotein

4. Cell to cell adhesion by glycoproteins

5. Some proteins are enzymes, hence they are called membrane bound enzymes e.g. sucrase enzyme in the

cell surface membrane of intestinal cells.

6. They act as hormone binding sites i.e. hormone receptors

7. They are electron carriers in the membrane

8. Some act as antigens.

Carbohydrates in the cell surface membrane

- These carbohydrates are polysaccharides,

- They occur either in association with proteins (glycoproteins) or lipid (glycolipids)

- Glycoproteins and glycolipids are collectively kwon as glycocalyx

- The roles of glycocalyx are:-

a) Cell to cell recognition

b) Cell to cell adhesion

c) Act as receptors

d) Acts as antigens

Fluid mosaic model of the structure of the cell membrane

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- This is currently an accepted model of the structure of the cell membrane.

- The membrane is fluid because:

The phospholipids move around the membrane making the cell membrane to be constantly in

motion.

- The membrane is mosaic because:

Different types of proteins lie among the phospholipids in the membrane.

Question

Explain why a membrane may be more fluid when it contains more unsaturated fats.

Unsaturated fatty acids contain at least one double bond in the carbon chain

The more the unsaturated lipids there are in the membrane, the more fluid the membrane is.

Role of fluidity in membranes

- Phospholipids in membranes are in fluid state.

- The importance of fluidity of the membranes are:

a) Allows membrane to change shape i.e. during active transport and facilitated diffusion.

b) Allows vesicles to be pinched off from the membrane e.g. during endocytosis.

c) Allows vesicles to fuse with the membranes during exocytosis.

Evidence that have been important in building up the fluid mosaic model

a) The membrane is fluid;

1. Membranes join when the cells fuse together.

2. Change in position of marked proteins (they intermingle or mix) when cells fuse.

3. Sealing of the membrane after puncturing it with a fine needle.

4. Fusion of vesicles and membrane during exocytosis.

5. Breakage of membrane during endocytosis.

b) The membrane is a phospholipid bilayer

1. Phospholipids at an air/water surface form a monolayer with hydrophilic heads in the water and

hydrophobic tails in the air; so, the phospholipids form a bilayer with the hydrophobic tails hidden

away from the solution and the hydrophilic heads in the solution.

2. Lipids extracted from red blood cells cover an area of about twice the size of the cell; so, the

membrane must be a phospholipid bilayer.

c) Proteins are carriers in the membrane

1. Large uncharged molecules and ionic molecules can only cross the membrane if protein carriers and

protein channels exist; so, there are protein molecules in the phospholipid bilayer that act as carries and

channels, respectively.

d) Large part of the membrane is made up of lipids.

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1. Lipid soluble substances pass through the membrane more easily than other substances; so, a large part

of the membrane must be made up of lipids.

Question

1. Describe the role of fluidity of membranes?

1. It allows the membrane to change shape during active transport and facilitate diffusion.

2. Allows vesicles to be pinched off from the membrane during endocytosis.

3. Allows vesicles to fuse with the membranes during exocytosis.

2. Describe what is meant by fluid mosaic model

- It is fluid because the phospholipids move around the membrane making the cell

membrane to be constantly in motion.

- It is mosaic because different types of proteins lie among the phospholipids in the

membrane.

3. Membranes with more unsaturated fatty acids are more fluid. Discuss?

- They have double C-C bonds in the chain that would cause kinking hence more fluid.

4. Why do phospholipids form a bilayer and not a monolayer in the membrane?

- This is due to the nature of the phospholipids whose phosphate heads are hydrophilic

hence face polar environments (tissue fluid and cytoplasm) and the fatty acid tails are

hydrophobic hence face inwards (non polar environment)

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TRANSPORT ACROSS MEMBRANES

There are 6 mechanisms of transporting substances across membranes

1. Diffusion

2. Facilitated diffusion

3. Active transport

4. Osmosis

5. Endocytosis

6. Exocytosis

NB

Diffusion facilitated diffusion and osmosis don’t use energy hence they are called passive processes. Active

transport, endocytosis and exocytosis uses energy hence they are called active processes.

Diffusion

- This is passive movement of small uncharged particles (small non polar particles), down their concentration

gradient until equilibrium is achieved.

- These particles are able to move as a result of their random motion of particles and the energy for this random

motion comes from the kinetic energy of molecules involved

- These substances pass between the phospholipids

- These substances that move through by diffusion include:

a) Oxygen

b) Carbon dioxide

c) Water

Water can be transported through by

a) Diffusion

b) Facilitated diffusion through channel proteins

- water is transported easily through diffusion when the phospholipid bilayer contains phospholipids with

unsaturated fatty acids hydrocarbon tails because they are more spaced

- CO2 is polar but its small size thus allows diffusion

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Facilitated diffusion

Large polar molecules and ions that is larger than CO2 molecules that cannot move across a membrane by

diffusion. They are insoluble in lipids and therefore the hydrophobic tails of phospholipid provides a penetrable

barrier to them. They cross the membrane with the help of proteins through a process called facilitated diffusion.

These proteins are channel proteins (ion channels) or carrier proteins.

a) Channel proteins

They transport small charged molecules or ions through the channel that is polar channel proteins are specific i.e

transport only one molecule or ion e.g. Na channel is a protein that only transport Na+ ions down the concentration

gradient. Chanel proteins are divided into two

a) Gated – open and close depending on the presence of the substance

b) Fixed – always remain open

To show that channel proteins are specific, the following experiment can be conducted

- The concentration of the 3 mineral ions in a seedling are determined e.g nitrates (NO3-5 units phosphates

(PO43- 5 units and magnesium (Mg2+) 5 units

- The concentration of these ions in the beaker are also determined e.g nitrates – 10 units, phosphates – 10 units

and magnesium – 10 units.

- The seedling is placed in the beaker and left for days.

- The results are shown below.

NO3- PO43- Mg2+

Beaker

Plant (seedling)

7.5

7.5

8.0

7.0

9.0

6.0

The results shows that

1. The ions are being absorbed through facilitated diffusion because with nitrates, equilibrium has been

achieved

2. The absorption of the nitrate ions (NO3-) is faster than other minerals

3. Due to different concentration of the ions inside the plant, the 3 ions are transported by different channel

proteins i.e channel protein are specific to ions.

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NB

In facilitated diffusion, no metabolic energy is used and the movement of ions is down the concentration gradient.

b) Carrier proteins

They transport large polar molecules such as amino acids and glucose. These carrier proteins are specific for

particular molecules. Once a carrier protein has picked up a molecule, it changes shape and act as a pore for the

molecule to travel through the membrane. There is no use of metabolic energy and the movement is down the

concentration gradient

Example of diffusion include:

1. Gas exchange in the lungs between the alveoli and the capillaries.

2. Gas exchange in the leaves of flowering plants between the air spaces and the spongy mesophyll tissue

and the mesophyll cells

The requirements for diffusion /facilitated diffusion to occur are

1. Concentration gradient of the substance

2. Permeable membrane

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Osmosis

This is the passive movement of molecules of water down their concentration gradient through a partially

permeable membrane.

Osmosis is due to the random movement of water molecules across the membrane. If solute molecules are present,

water molecules from hydrogen bonds with them, and this reduces the movement of these water molecules.

Examples of osmosis include:

a) Absorption of water molecules by animal and plant cells

b) Absorption of water molecules by the plant roots from the soil

Describing concentrations

1. Isotonic solution

This is the solution that has the same osmotic concentration of the solution as the cell i.e there is equilibrium hence

no net movement (no osmotic gradient)

2. Hypertonic solution

This is the solution with the higher concentration of solutes than the cell, and therefore water will move from the

cell to the solution, and the animal cell shrinks (crenated) and the pant cell shrinks (becomes flaccid) and is finally

plasmolyzed (cell membrane moves away from cell wall).

- The number represents solute, not water

- Arrow shows movement of water

3. Hypnotic solution

This is the solution with less solute than the cell and thus it has more water then the cell. So, water will move from

the solution into the cell causing the cell to become turgid (full of water) and finally the animal cell bursts, but the

plant cell remains turgid as it cant burst due to cellulose cell that provides mechanical strength to the cell.

Water potential

This is the ability of water to move. Its measured in units of kPa (pressure), kilo Pascals. Pure water has the

highest water potential i.e OkPa so, all the solution have negative water potentials.

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Questions

1. List differences between osmosis and diffusion

- Osmosis transports water molecules only, while diffusion transports many small uncharged molecules

- Osmosis uses a partially permeable membrane but not diffusion.

2. List the differences between osmosis and facilitated diffusion

- Osmosis transports water only whilst facilitated diffusion transports many polar molecules that are larger than

CO2 and cannot pass through by diffusion.

- Osmosis uses a partially permeable membrane, but facilitated diffusion does not need one

- Facilitated diffusion uses protein, osmosis does not.

3. List the similarities between osmosis and diffusion

- Both don’t use ATP energy

- Movement of molecules is down a concentration gradient

Differences

Osmosis Diffusion Osmosis Facilitated diffusion

Transports water

molecules

Transports small

uncharged molecules

Transports water

molecules only

Transports are polar

molecules (>CO2)

Partially permeable

membrane

None Partially permeable

membrane

None

None Uses proteins to

transport molecules

across the

membranes.

Active transport

This is the movement of particles against their concentration gradient using metabolic energy in the form of ATP. It

involves carrier proteins that span (cut by the whole bilayer) the membrane.

Carrier proteins, also called protein pumps, are specific as they transport only one substance e.g. Na pump, K

pump.

ATP is hydrolyzed by ATPase enzyme to release energy that enables the carrier protein to change shape

and act as a pore for the molecule to travel through the membrane.

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Example of active transport are:-

a) Selective reabsorption of glucose, sodium and amino acids in the kidneys

b) Absorption of glucose in the small intestine

c) Absorption of mineral salts by the plant roots from the soil

Questions

1. Describe the process of active transport

- Transport of particles against their concentration gradient

- It uses energy in the form of ATP

- Movement is in one direction (no equilibrium)

- It involves a carrier protein that spans across the membrane

- Molecules bind to the protein

- Protein changes shape to transport molecules

- Example : sodium pump

2. What is the role of active transport

It makes it possible for cells to move substances across the membrane against their concentration gradient. It also

moves substances which could not otherwise pass through the membrane.

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3. List the differences between active transport and facilitated diffusion

Differences

Active transport Facilitated diffusion

Particles move against the concentration

gradient

Particles move along down their concentration

gradient

uses ATP energy No energy used (passive)

Has no equilibrium Has an equilibrium

4. Write the major similarity between facilitated diffusion and active transport

Both use proteins

Bulk transport

- Diffusion, osmosis and active transport allow for the movement of small particles across the membranes

- However, there are times when larger particles need to be transported across the cell surface membrane

- This is achieved by bulk transport i.e endocytosis and exocytosis which rely on the fluid nature of the

membrane. This transport requires metabolic energy.

Endocytosis

This is the movement of materials into a cell by a process in which the plasma membrane engulfs extra cellular

materials forming membrane bound sacs (vesicles) that enter the cytoplasm.

There are 2 forms of endocytosis

a) Phagocytosis (cell eating)

This involves the absorption of large solid materials e.g a white blood cell engulfing a bacterium

b) Pinocytosis (cell drinking)

This involves absorption of liquids e.g amoeba absorbing liquids across its cell surface membrane. They are also

taken into the cell by tiny vesicles produced by the cell surface membrane.

Exocytosis

This is the movement of materials out of the cell by a process in which intracellular materials are enclosed within a

vesicle that moves to the plasma membrane and fuses with it, releasing the materials out of the cell, example

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hormones in the cell are enclosed by vesicles which move to the plasma membrane, fuse with it and release their

contents

Questions

1. Explain how endocytosis and exocytosis provides evidence for the fluid mosaic model of membranes.

Endocytosis and exocytosis involves the breaking and fusing of parts of the cell surface membrane. If the

membrane was not fluid this would not be possible.

2. What are the similarities and differences between exocytosis and endocytosis

Endocytosis Exocytosis

Both use metabolic energy (ATP)

Both transport substances in vesicles

Both transport large molecules

Substances taken into cell Substances removed out of cell

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DIFFUSION AND GASEOUS EXCHANGE

Question

1. List three areas in humans where gaseous exchange occurs

a) Between alveoli in the lungs nod the surroundings capillaries

b) Between the blood and the tissue fluid

c) Between the cell (in the tissue) and the tissue fluid

2. Write down the name of the process by which gases are exchanged

Diffusion

3. Describe the process of gaseous exchange in very small organisms

Diffusion due to the large S.A to volume ratio

Diffusion is not only for the exchange of the gases (CO2 and O2) but also the movement of the gases in the small

organisms.

4. Describe the process of gaseous exchange in larger organisms as humans

Due to small S.A to volume (v) ratio, humans cannot only use diffusion for the exchange of gases. They require

(i) Respiratory system to exchange with the environment

(ii) Circulatory system to move these gases around the body

5. List the components of the respiratory system and the processes that take place in those components

(i) conducting system which consist of breathing tubes and cavities :- breathing or ventilation

takes place there

(ii) interface (alveoli and capillaries) gaseous exchange takes place there through diffusion.

6. List the gaseous exchange surfaces in organisms

(i) Alveolus in humans

(ii) Gills in fish

(iii) Leaf in plants

7. List 3 properties of gaseous exchange surfaces

a) Large surface area (SA)

Rate of diffusion is directly proportional to the SA. As the SA increases, diffusion increase i.e the bigger the SA the

more the particles that can be exchanged at the same time.

b) Thickness of gaseous exchange surfaces

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Rate of diffusion is inversely proportional to thethickens of the gas exchange surface. The thicker the surface, the

slower the diffusion, and the shorter the diffusion distance, the faster the diffusion can take place.

c) Concentration gradient of particles

Rate of diffusion is directly proportional to the difference in concentration across the gas exchange surface. The

greater the concentration gradient, the faster the diffusion.

8. Define Fick’s law and describe how it relates to humans

Definition – there are of diffusion is directly proportional to the SA multiplied by the concentration difference

divided by the distance the substance has travelled. So the rate of diffusion will increase with increasing SA and

concentration gradient and decrease with increasing distance

Rate of diffusion =S.A x concentration gradient divided by thickness of exchange membrane

How it relates to humans

- The alveoli in the lungs provide a large SA for the exchange of gases. The capillaries surrounding the alveoli

maintain a steep concentration gradient they continuously carry away oxygen from the lungs and ring in CO2

continuously from the body.

- The walls of the alveoli and the walls of the capillaries surrounding the alveoli are only 1 cell thick, so the

diffusion distance of gases is very small.

9. Describe how a mammalian lung is adapted for rapid gaseous exchange

a) Large surface area

- The alveoli provides a large SA for the exchange of gases in the human body

- An adult has around 480 to 500 million alveoli in the lungs which gives a large SA for gaseous exchange of

around 100m3 packed into a chest

b) Short diffusion distance

The walls of the alveoli and the walls of the capillaries surrounding them are only 1 cell thick so the distance the

diffusing gases have to travel between them is about 0.5dm to 1.5dm.

c) Steep concentration gradient

Capillaries surrounding the alveoli maintains cone gradient. This is because they continuously bring in CO 2 from

the body and continuously carry oxygen away from the lungs to the body maintaining a steep concentration

between them and the alveoli.

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Human respiratory system

The human respiratory system consists of

a) Conducting systems

- A pair of nostrils

- A single nasal cavity

- Pharynx (back of mouth or throat)

- Larynx (voice box)

- Trachea

- Bronchi

- Bronchioles

b) Interface

- Alveoli and the capillaries surrounding them

In the conducting system, ventilation/breathing takes place while in the interface gaseous exchange takes place.

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Ventilation or breathing

This is a process of taking air rich in oxygen into the lungs and removal of air rich in carbon dioxide from the lungs

back into the air or atmosphere. Ventilation or breathing takes place in the conducting system of the human

respiratory system, ventilation consists of

a) Inhalation/inspiration/breathing in

b) Exhalation/expiration/breathing out

a) Inhalation /inspiration/breathing in

This is the taking in of air rich in oxygen into the lungs. Its an active process because it involves contraction of

muscles.

External intercostals muscles contract forcing the ribs to move up and out. Diaphragm muscles contract, lowering

the flattening the diaphragm.

The above two events increase the volume of the chest cavity and decrease the pressure forcing the air to enter the

lungs through the conducing system.

Exhalation/expiration/breathing out

This is the removal of air rich in carbon dioxide from the lungs.

Normal exhalation is a passive process because it involves the relaxation of the muscles that had contracted during

inhalation.

The external intercoastal muscles relax so the ribs move downwards and inwards. Diaphragm muscles relax and the

diaphragm becomes dome shaped. The above two events reduce the volume of the chest cavity and increase the

pressure, and air is forced out.

Forced exhalation is an active process that requires

a) Internal intercostal muscles contract pulling the ribs downwards and inwards

b) Abdominal muscles contract forcing the diaphragm upwards

The above two events increase pressure in the chest cavity and decreases the volume causing exhalation.

Preparation of air before reaching the lungs

Preparation of air before entering the lungs ensures that the inhaled air does not change the internal environment.

These preparations are carried out by the conducting system or air passage.

These preparations include

a) The air must be clean by the removal of micro organisms and other particles.

This cleaning is done by

(i) Nose hair

(ii) Mucus produced by the gablet cells that trap these particles

(iii) Cilia of epithelial cells. The wafting like beating of cilia moves the dirty mucus to the mouth cavity

where it is either coughed to/swallowed, thus reducing the risk of infection of the lungs.

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Acid in the stomach kills most of the micro organisms swallowed

b) The air is moistened. (The level of water vapour in the air is increased.

The air is moistened by moist surface. The moist surface is due to the moist lining (produced by the goblet cells.

c) The air is warmed by a good supply of blood in the nasal passage’s

This raises the temperature of the air

NB

The nose provides a large SA for the preparation of air to be inhaled.

Gaseous exchange in the interface

This involves the alveoli (air sacs) and the surrounding capillaries.

The exchange of these gases CO2 and O2 is though diffusion.

Capillaries maintain step concentration gradient of these gases between the capillaries an the alveoli in the

following ways;

(i) They continuously carry oxygen from the lungs to the body so that there is less oxygen in the

capillaries than the alveoli therefore creating concentration gradient hence diffusion.

(ii) They continuously bringing carbon dioxide to the lungs fro the body so that there is always more CO2

in the capillaries than the alveoli creating a concentration gradient hence diffusion.

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HOW LUNG SURFACTANT PREVENTS THE COLLAPSING OF THE ALVEOLI

The moist lining and the alveolar lining attracts one another by adhesion (attraction of non-similar molecules) and

this can collapse the alveoli and reduce gaseous exchange.

However, to reduce the collapse, some cells in the alveolar lining produce a special phospholipid known as lungs

surfactant. The surfactant coats/lens the alveoli to reduce adhesion so that gaseous exchange is easier.

Composition of gases

Gas % percent of gas

Inspired air Alveolar air Expired air

Oxygen 20.70 13.20 14.50

Carbon dioxide 0.04 5.00 3.10

Nitrogen 78.00 75.60 75.40

Water vapour 1.26 6.20 6.20

- Inspired air has more oxygen than expired air by 6.2%. This percent is used for respiration in the respiring

tissues. Alveolar air has less oxygen as oxygen diffuses in to the capillaries

- Alveolar air has more carbon dioxide than both inspired and expired air. This is because carbon dioxide

diffuses from the capillaries into the alveoli.

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Regulation of water in mucus in the lungs

- Mucus should not have excess or too little water in the lungs

- The membrane of the epithelial cells is the one that detects the amount of water in the mucus and then it

triggers the corrective measures.

- However, a person with cystic fibrosis (cf) cannot regulate water in the mucus. In such a person the mucus has

very little water causing thick and sticky mucus that blocks the air ways.

Cystic fibrosis

- It is a genetic disorder caused by a gene mutation (deletion) in the gene which codes for a protein known as the

chloride channel or CTR protein (cystic fibrosis transmembrane regulator protein)

- The protein is involved in the transport of chloride ions through the cell surface membrane.

- The CFTR protein has a binding site for ATP. ATP binds the site and it is hydrolysed to get energy that

changes the shape of the CFTR protein so that it opens to allow for the passage of chloride ions.

- The gene mutation of the CFTR protein cause the loss of ATP binding site in the CFTR protein so that it

remains closed. This cause the chloride ions to remain in the cell

- So, chloride ions remain in cells and cannot diffuse into the mucus and therefore water cannot move into mucus

by osmosis and instead the water leaves the mucus into the cells (epithelial cells) by osmosis leaving behind

thick and sticky mucus in the airways that block them.

-

NB

The ATP in the CFTR protein provides energy by the change of the shape of this protein so that it opens up.

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Why CF lungs cannot regulate water in the mucus

1. Cl- pumped into epithelial cell from tissue fluid across the basal membrane but cannot diffuse into mucus

due to non-functional CFTR protein.

2. Na+ diffuses from mucus into epithelial cell

3. Water diffuses from mucus into epithelial cell by osmosis

4. Chloride pump

5. Chloride channel (CFTTR protein)

6. Sodium pump

7. Sodium channel

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Proteins

They are very large (macro molecules) organic molecules made up of:

1. Carbon

2. Hydrogen

3. Oxygen

4. Nitrogen

- In addition to these elements, other proteins have sulfur, iron and phosphorus

- Proteins have a wide range of functions in living things. About 18% of body is made up of protein. Some of these

functions of protein include:-

1. Formation of enzymes – they speed up chemical reactions of the cells

2. Formation of hormones – control working of organs

3. Formation of antibodies – protect us from diseases

4. Formation of hemoglobin – transports oxygen and carbon dioxide

5. Formation of prothrombin – used for blood clotting

6. Proteins in cell membranes - these are involved in transportation, structure of the membrane and cell to cell

recognition.

7. Making proteins in hair, skin, nail etc

Amino acids

- These are small monomer units that join by peptide bonds in condensation reactions to form proteins

- There are about 20 different naturally occurring amino acids that can combine in different ways to form a vast range of

different proteins.

- All amino acids have the same basic structure i.e. there is always an amino group (NH2) and a carboxyl group (COOH)

attached to a carbon atom. The R- group (residual group or side chain) is the only group in all amino acids that varies

between amino acids.

- The R-group has the following functions

1. It determines the bonding between amino acids in the protein

2. It’s a receptor in the cell surface membrane

3. It’s an active site in enzymes

- The chemical formula of all amino acids in NH2 – RCH – COOH

Characteristics of amino acids

- They are small molecules that can easily pass through the cell membrane

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- They are soluble in water because the NH2 and COOH groups are polar

- They can crystallize

- Some amino acids have polar R groups while others have non polar R groups.

- Amino acids are amphoteric (compounds with acidic and basic groups). The NH2 group is basic as it readily accepts

protons (H+ ions) while COOH group is acidic as it readily donates protons. The amino acid therefore acts as a buffer

substance. A buffer substance is a substance that maintains a constant pH.

- The charge of the amino acid depends on the pH of the medium of which it is placed.

- This is because the pH of the medium determines the manner in which the NH2 and COOH groups ionize.

a) Amino acids in neutral medium

In neutral medium, the amino acid is ionized i.e. ionized amino acid/neutral amino acid/zero charge amino acid/double ion/

zwitterion amino acid. In the animal cells, the pH of the cytoplasm is usually neutral so both NH2 and COOH become ionized.

b) Amino acid in acidic medium

c) Amino acid in basic medium

For each amino acid, there is a specific pH value at which the amino acid has a zero charge (ionized amino acid). The pH value

at which the amino acid is neutral is known as the iso electric point of the amino acid.

Formation of peptide bond and dipeptide molecule

- Amino acids are joined by a peptide bond to form a dipeptide molecule or a polypeptide molecule in a condensation

reaction.

- A dipeptide molecule has 2 amino acids joined by a peptide bond while a polypeptide molecule is a long chain of amino

acids joined by a peptide bond.

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STRUCTURE OF PROTEINS

There are 4 levels of protein structures

1. Primary structure

2. Secondary structure

3. Tertiary structure

4. Quaternary structure

1. Primary structureThis is the sequence of amino acids joined by peptide bonds to form a polypeptide chain.

Primary structure is not affected by high temperature because the peptide bonds are not affected by this temperature and therefore even after heating, the length remains the same.

2. Secondary structureThis is 3D structure formed by either coiling of the structure to form alpha helix such as keratin held together by hydrogen bonds; or joining of several primary structures to form beta pleated sheets such as collagen held in place by hydrogen bonds.

Examples of proteins with - Helix structures are

1. Keratin – found in the skin, hair, nails, hooves, beaks and horns to give support

2. Myosin – found in muscles fibres to allow movement

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Examples of proteins with pleated sheets are

Collagen

- found in skin, tendons and bone to provide strength

- collagen is made up of 3 polypeptide chains forming a triple helix tropocollagen

Proteins with secondary structure are long (fibrous) and they have a role in support to give mechanical strength. In addition they are insoluble in water and they are affected by high temperature as it breaks down hydrogen bonds causing them to lengthen (they stretch out after heating).

Summary of secondary structures

1. Are - Helix and pleated sheets

2. Held by hydrogen bonds

3. Fibrous (long)

4. Involved in structural support

5. Are insoluble in water

3. Tertiary structureThis is a globular (spherical) structure formed by folding of the polypeptide chain already in secondary structure, and it is held in place by hydrogen, ionic and disulphide chemical bonds and hydrophobic interactions.

The amino acids have R- groups between which chemical bonds are formed. So, R-groups determine the types of chemical bonds, the chemical bonds determine the structure/ shape of protein and this structure determines the function of the protein.

High temperature, extreme pH and heavy metal ions such as copper change the shape of the globular protein.

Examples of protein with tertiary structure are enzymes such as amylase, antibodies and some hormones such as glucagon.

Being globular, proteins with tertiary structure have a role in metabolism e.g. enzymes speed up chemical reactions in the cells and glucagon raises blood glucose levels in the cells.All proteins with tertiary structures are soluble in water.The solubility of proteins with tertiary structure is because the polar R-groups face outwards and the non-polar R-groups face inwards in the protein

4. Quaternary structureThis is globular structures that consist of more than one polypeptide chain already in the tertiary structures, and these globular structures are held loosely by hydrogen, ionic and disulphide bonds and hydrophobic interactions.

Examples of proteins with quaternary structures are haemoglobin with 4 polypeptide chains and insulin with 2 polypeptide chains.

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Being globular, they have a role in metabolism. In addition they are soluble in water.

- Examples of proteins with quaternary structures are

1. Hemoglobin – has 4 polypeptide chains: 2 (141 amino acids ) and 2 (146 amino acids)

2. Insulin – has 2 polypeptide

chains: A and B. A has 21 amino acids and B has 30 amino acids.

Fibrous and globular proteins

1. Fibrous proteins

- They are long (fibrous)

- Are tough hence have structural role

- Insoluble in water

- Found in tendons, bones, muscles, hair, nails, horns, skin, beaks, hooves etc.

2. Globular proteins

- They are spherical /compact

- Soluble in water

- Are involved in metabolism e.g. enzymes are involved in catalysis

- Example

1. Enzymes such as amylase

2. Antibodies

3. Some hormones such as glucagon and insulin

3. Conjugated proteins

- Consist of amino acids and other non-protein chemical groups (prosthetic groups)

- Examples of conjugated proteins are

1. Haemoglobin – prosthetic group is haem group that contains iron. Oxygen binds to iron

2. Glycoprotein – prosthetic group is carbohydrate

3. Lipoprotein – prosthetic group is lipid

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Chemical bonds in proteins

1. Hydrogen bond

- These are weak electrostatic forces of attraction between the negative charges on the oxygen atom of the carboxyl group

of the amino acids and the positive charge on the hydrogen atom of the amino groups of the amino acids. When these

charged groups are close to each other, the opposite charges attract forming a hydrogen bond.

- Hydrogen bonds are weak but when they are in large numbers, they are very strong.

- Hydrogen bonds are easily broken and reformed if pH and temperature conditions change.

- Hydrogen bonds are important in the folding and coiling of the polypeptide chain

2. Sulphur bridges

- They are formed when two sulfur containing amino acids called cysteine or 2 methionine molecules are close together in

the structure of a polypeptide.

- An oxidation reaction takes place between the 2 sulfur containing groups, resulting in a strong covalent bond known as a

sulfur bridge or disulfide link

- These sulfur bridges are much stronger than hydrogen bonds and ionic bonds but they occur less (they are less in number).

- They are important for holding the folded polypeptide chain in place.

- They are the strongest bonds.

3. Ionic bond

- They are formed between strong positive and negative R-groups of amino acids, found buried deep in the protein

molecule.

- These links are also known as slat bridges

- They are strong bonds but not as common as the other structural bonds.

Structural differences between collagen and insulin

Collagen Insulin

1. Fibrous Globular

2. Have hydrogen bonds Have sulfur bridges

3. Have three polypeptide chains Have 2 polypeptide chains

4. Has more than 100 amino acids Has 51 amino acids

5. Has repeated sequences of amino acids Does not have repeated sequences of amino acids

Functional differences between collage and insulin

Collagen Insulin

1. Has structural function in tendons, bones,

skin etc.

Lowers blood glucose levels

2. Insoluble in water Soluble in water

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Enzymes

- These are globular proteins that act as biological catalysts to speed up chemical reactions by reducing the activation

energy and themselves don’t change shape or get used up in the reaction.

- Activation energy is the energy required to start reaction.

- A catalyst is a substance that speeds up a reaction by lowering the activation energy without changing the substance

produced, and is left unchanged at the end of the reaction.

- Enzymes, being biological catalysts, are specific in action i.e they catalyze a specific reaction or a group of reactions. So

enzymes show a great specify.

How enzymes speed up chemical reactions

- Most of the reactions that occur in living organisms are endogenic i.e require an input of energy to activate the molecules

in order to make them reactive. The free energy that is needed to raise the substrate to the activates state is known as

activation energy. This means that there is an activation energy barrier in a biological reaction.

Enzymes therefore lower the activation energy barrier so that the reaction is speeded up. By lowering the E A barrier,

enzymes make it easier for the substrate molecules to reach the activation state

EA Activation energy

Reactions in the cell

The total sum of all chemical reactions in the cell is labeled as metabolism

Anabolic + catabolic = metabolic

Metabolism is divided into two:

(i) Anabolism

The synthesis of complex molecules from simple molecules e.g synthesis of proteins (complex molecules) from amino acids

(simple ones) in an anabolic reaction.

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(ii) Catabolism

- It’s the break down of complex molecules into simpler ones e.g. break down of glucose (complex molecules ) into ATP

(simpler ones) in a catabolic reaction (or glycogen into glucose e.g. respiration)

- Metabolic pathway is the sequence of chemical reactions in a cell and each of these reactions is controlled or catalyzed by

a specific enzyme e.g. aerobic respiration is a metabolic pathway (chain).

Structure of enzymes

- Enzymes are 3d (globular) proteins that have tertiary structure of proteins

- Due to their tertiary structures enzymes have a specific shape and this means that they can only catalyze

specific reactions.

- An enzyme has a binding site called an active site onto which a substrate molecule binds or a reaction to occur.

Only a specific substrate binds to a specific active site of the enzyme for a reaction to occur and therefore

enzymes activity is based in lock and key mechanism i.e the lock is the enzyme, the key hole is the active site

and the key is the substrate.

- However, in few enzymes, the active site can change shape or is modified so that a substrate molecule can

bind to it. This mechanism of enzyme activity is called included fit mechanism. So this mechanism shows no

specificity. Once the products leave, the active site reverts to its former shape.

- Apart from the active site, the other part of the enzyme is called the allosteric site.

Formation of enzyme –substrate complex

A substrate binds to a specific active site to form an enzyme – substrate complex. Due to kinetic energy of the

enzymes and substrate molecules, there are random collisions that lead to the binding of the substrate to the active

site.

Hydrogen bonds and vander waals forces of attraction are formed between the substrate and active site forming

enzyme substrate complexes and the reaction occurs to form a product. The product detaches from the active site

and the enzyme is available for other reactions. So, enzymes are not used up or changed in the reaction they

catalyze.

Enzyme + substrate enzyme – substrate enzyme – 2 products

Complex (maltose- maltose glucose

Maltose) molecules

The active site and substrate have a complementary shape NOT the same shape!!

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The modes of action of enzymes are:-

1. Lock and key mechanism

2. Induced fit hypothesis

Groups of enzymes

There are two major groups of enzymes:-

(i) Intracellular enzymes

Are synthesized and work inside the same cells e.g DNA polymerase and DNA ligase

(ii) Extracellular enzymes

Formed in the cells and secreted through exocytosis to work elsewhere e.g the digestive enzyme such as amylase

and lisozyme in the tears.

Naming enzymes

1. Using the molecule hat the enzymes work on (the substrate) with (-ase) on the end, e.g sucrose (roks on

sucrose) or the substrate with an indication of what it does e.g creatine kinase

2. Using the type of reaction being catalyzed e.g ATP; creatine, phosphotransferase

3. A classification number e.g EC 2.7.3.2

Characteristics of enzymes

1. All enzymes are globular proteins. Enzymes have an active site and alosteric site. Active site is where a

substrate binds and therefore high temperature changes the shape of enzyme and also changes the shape of

the active site. So the substrate cant bind. This is known as the denaturation.

2. Enzymes only change the rate of a reaction by speeding it up. They don’t alter the end products that are

formed.

3. They do not change or get used up in a chemical reaction that they catalyze

4. They are specific to the reaction that they catalyze. They show high specifity in their action.

5. They are affected by high temperature, extreme pH and heavy metals.

Factors that affect enzyme activity

1. Temperature

2. pH

3. substrate concentration

4. enzyme concentration

5. inhibitors

Effects of temperature on enzymes activity

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The effect of temperature on the rate of any reaction can be expressed as the temperature co-efficient, Q10. This is

expressed as:-

Q10 = rate of reaction at (x -10) 0 c

Rate if reaction at x0c

Between 00c and 400c (except for thermophilic bacteria which can withstand about 850c), Q10 for any reaction is 2.

In other words, in that temperature range every 100c rise in temperature produces a doubling of the rate of reaction.

Beyond 400c, the enzyme catalyzed reaction decrease and at about 600c het reaction has completely stopped.

At temperatures over 400c, most proteins including enzymes start to lose their tertiary and quaternary structures.

The shape of het enzyme changes and thus the shape of the active site changes so no substrate can bind to this

active site. This is known as denaturization.

a) At low temperature there is less kinetic energy of het enzyme and substrate molecules giving rise to

reduced random collisions that forms less enzyme substrate complexes, generating less products.

b) As the temperature increases, the kinetic energy of molecules increases leading to more random collisions

that forms more enzyme substrate complexes, generating more number of complexes hence formation of

more products.

c) At the optimum temperature, there is maximum kinetic energy of molecules giving rise to maximum

random collisions , hence maximum number of enzyme – substrate complexes that gives rise to maximum

formation of products.

d) At high temperature, there is intense/excessive kinetic energy leading to violent random collisions or

vibrations that break the bonds that maintain the globular structure of the protein (enzyme). This changes

the shape of the enzyme and hence the shape of the active site so that the substrate cannot bind. This is

denaturation.

NB

Most enzymes have their optimum temperature between 30 and 400c. at very low temperatures the enzyme is

inactive. At very high temperature the enzyme is denatured. Each enzyme has its own optimum temperature.

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Effects of pH on enzyme activity

- Different enzymes have different optimum pH levels. E.g the optimum pH for enzymes in the human stomach

is 2, while the pH for enzymes in the human mouth cavity and duodenum is 7.5.

- Deviation from the optimum pH alters the ionization of amino acids that make up these enzymes. The change

in ionization of amino acids breaks down hydrogen bonds, ionic bonds and sulfur bridges leading to loss of

globular shape of enzymes hence denaturation.

Effects of substrate concentration on enzyme activity

If the enzyme concentration remains the same but the substrate concentration increases the rate of reaction will

increase as the substrate concentration increases but only until all the active site of the enzymes are saturated or

fully occupied by the substrate. At this point, the enzyme concentration is limiting but the substrate concentration

is not limiting.

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At this point the enzymes are working as fast as possible (maximum reation0 hence there is maximum formation of

products. This maximum rate of reaction is known as Vmax.

NB

In addition of enzymes will provide more active sites and the rate of reaction will not level off

Effects of enzyme concentration on enzyme activity

If the substrate concentration remains the same but the enzyme concentration increases, the rate of reaction will

increase but only until all the substrate molecules are used up; so, it’s the substrate concentration that is limiting not

the enzyme concentration.

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Vmax = max rate of reaction

Substrate concentration

Rate of reaction (v)

No Vmas

Substrate concentration

Rate of reaction (v)

Rate of reaction

NB

If more substrate molecules are added, the rate of reaction will continue to increase

Effects of inhibitors on enzyme activity

Inhibitors are substances that reduce the activity of enzymes. There are two types of inhibitors

(i) Active site directed inhibitors

They compete for the same active site as the substrate because the inhibitor and the substrate have similar shape. It

blocks the active site so that the substrate cannot bind and this stops the enzyme activity. These inhibitors do not

alter the shape of the active site hence no denaturation of enzymes. This inhibition is reversible if there is addition

of more substrate molecules.

(ii) Non active site inhibitors

These inhibitors bind to the allosteric site causing the change of the shape of enzyme hence they change the shape

of the active site causing denaturation. This inhibition is irreversible. These inhibitions are heavy metals such as

mercury, lead, copper etc. and chemical substances such as cyanide.

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Enzyme concentration

Enzyme concentration

Rate of reaction

NUCLEIC ACIDS

Nucleic acids are the genetic molecules of the cell.

They are concerned with inheritance.

There are two types of nucleic acids in the cells. These are;

(i) Deoxyribonucleic acid (DNA)

(ii) Ribonucleic acid (RNA)

Organelles with DNA

a) Nucleus

b) Nucleolus

c) Chloroplasts

d) Mitochondria

Organelles with RNA only

a) RER

b) Ribosomes

Organelles with DNA and RNA

a) Nucleus

b) Nucleolus

c) Chloroplasts

d) Mitochondria

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Chemical nature of nucleic acids

Nucleic acids are made up of mononucleotides (nucleotides).

A mononucleotide consists of the following:-

a) A phosphate (phosphoric acid)

b) A pentose sugar (ribose in RNA and deoxyribose in DNA)

c) Nitrogenous bases

Mononucleotide /Nucleotide

NB

The nitrogenous base combines with pentose sugar using a covalent bond to form a nucleoside that then

joins to the phosphate group using phosphoester bond/covalent bond to form a nucleotide or a

mononucleotide.

Pentose sugars in the nucleic acid

These are 5 carbon sugars

They are monosaccharides

They are divided into two;

(i) Ribose sugar in RNA

(ii) Deoxyribose sugar in DNA

The difference between ribose and deoxyribose is that ribose has 5 oxygen atoms while deoxyribose has 4

oxygen atoms i.e. carbon atom two does not have an oxygen atom on it.

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Organic nitrogen bases

Ribose sugar

Deoxyribose sugar

Nitrogenous bases in nucleic acids

There are two types of nitrogenous bases in nucleic acids:-

1) Purines

2) Pyrimidines

Purines

They have a double ring structure. They are;

a) Adenine (A)

b) Guanine (G)

The structure of purine is as follows:-

Both DNA and RNA have the same types of purines i.e. Adenine and Guanine

Pyrimidines

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They have a single ring structure. They are;

a) Cytosine (C)

b) Thymine (T) in DNA

c) Uracil (U) in RNA

The structure of pyrimidine is as follows;

Nitrogenous bases in DNA

a) Adenine (A) – purine

b) Guanine (G) – purine

c) Cytosine © - pyrimidine

d) Thymine (T) – pyrimidine

Nitrogenous bases in RNA

a) Adenine (A) – purine

b) Guanine (G) – purine

c) Cytosine (C) – pyrimidine

d) Uracil (U) – pyrimidine

DNA as a polymer of mononucleotides

Mononucleotides join through a condensation reaction to form a phosphodiester bond.

This bond is formed between the 3rd carbon of the deoxyribose of one mononucleotide and the phosphate group of

the other mononucleotide.

Several mononucleotides joined by phosphodiester bonds in a condensation reaction form a polynucleotide chain

/strand as shown below.

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Mononucleotides are named by their bases

The sugar (deoxyribose in DNA) and phosphate form the backbone of the molecule and this does not change.

Pointing inwards from this backbone are the nitrogenous bases which keep on changing so, mononucleotides are

given the names of their bases.

DNA is made up of two antiparallel polynucleotide chains

- A DNA molecule is made up of 2 polynucleotide chains/strands.

- The 2 polynucleotide chains are anti-parallel i.e. one chain runs from the 5’ to 3’ end, while the other runs from

3’ to 5’ end.

- 5’ to 3’ means that the 5th carbon atom of the pentose sugar is nearest to the end on one side, and the 3’ end

means that the carbon atom 3 of the pentose sugar is nearest to the end on the other side of the chain.

Double helix structure of DNA molecule

- These two anti parallel polynucleotide chains coil around each other to form the double helix structure of DNA.

- In this double helix structure, one complete turn consists of 10 base pairs.

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- These base pairs are joined by hydrogen bonds (i.e. the 2 polynucleotide chains are joined by hydrogen bonds

between the base pairs).

- The distance between the base pairs is 0.34nm.

- One complete turns is:

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Complementary base pairs

There is a fixed rule of pairing nitrogenous bases, mainly based on their mass i.e. bases with equal mass

pair up together.

A purine pairs up with a pyrimidine as shown below;

G C Triple hydrogen bond

C G = Double hydrogen bond

A T

T A

Question

In a DNA sample, the percentage mass of Adenine is 18%. What is the percentage mass of Guanine?

Adenine = 18% 100 – 36% = 64%

Thymine = 18% guanine + cytosine = 64%

Total = 36% Guanine = 64/2 = 32%

Ribonucleic Acid (RNA)

This is a single polynucleotide chain

They are shorter than DNA molecules hence have smaller molecular mass

The mononucleotides of RNA contain a pentose sugar called ribose.

The nitrogenous bases in RNA are:

A – Adenine

U – Uracil

G – Guanine

C – Cytosine

They pair up as follows;

A = U

G C

Unlike DNA molecules that is of one type there are 3 types of RNA in the cells:

(i) messenger RNA (mRNA)

(ii) transfer RNA (tRNA)

(iii) Ribosomal RNA (tRNA)

1. Messenger RNA (mRNA)

It is synthesized by the antisense DNA strand in the nucleus through complementary base pairs.

Its role is to carry genetic information from the antisense DNA strand in the form of codons (triplet of bases) to

the surface of ribosomes in the cytoplasm.

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The mRNA molecules are linear (straight chains) to ensure that the codons are exposed for reading and

translation of the codons into a sequence of amino acids.

During transcription (synthesis of the mRNA by the antisense DNA (5’-3’) strand through complementary base

pairing in the nucleus), enzymes known as DNA helicase and RNA polymerase are used.

2. Transfer RNA (tRNA)

It is synthesized by the DNA through transcription in the nucleus and then passes out to the cytoplasm.

The tRNA molecule is clover leaf shaped. When stretched out, it has 80 bases and it runs from 5’ to 3’ end.

At the 3’ end there is a free OH group which acts as a binding site for the amino acids.

The tRNA molecule also has anti –codon loop which consist of an anti-codon.

An anti-codon is a triplet of bases on tRNA which is complementary to the codon on mRNA.

Its function is to carry a specific amino acid from the cytoplasm to the ribosome and to attach to the

mRNA so that the amino acids are aligned correctly to form polypeptide.

3. Ribosomal RNA (rRNA)

It is synthesized in the nucleolus in the nucleus

Its function is to synthesize ribosomes

It is highly folded into a compact globular shape

Questions

1. List differences between DNA and RNA

DNA RNA

1. Has two polynucleotide chains that

form a double helix structure

Has one polynucleotide chain

2. It’s made up of bases A,T,G,C It’s made up of bases A, U, G, C

3. Has a deoxyribose sugar Has a ribose sugar

4. It is a longer molecule hence larger

molecular mass

It is a small molecule hence a smaller

molecular mass

5. One type Three types: mRNA, tRNA and rRNA

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2. Write down 4 differences between mRNA and tRNA

The mRNA The tRNA

1. Straight chain Clover leaf shaped (folded)

2. It is of variable length Fixed length (80 bases)

3. Usually a long chain Usually a short chain

4. No hydrogen bonds Has hydrogen bonds

SEMI CONSERVATIVE REPLICATION OF DNA

DNA helicase breaks the hydrogen bonds between base pairs to separate the 2 strands of DNA and expose

bases.

The two DNA strands act as templates to synthesize new DNA molecules.

Mononucleotides bind to complementary mononucleotides of the DNA template strands.

DNA polymerase and DNA ligase catalyze the synthesis of phosphodiester bonds between these

mononucleotides from 5’ to 3’ and 3’to 5’, respectively, forming a leading strand and a lagging stand,

respectively.

Each new DNA molecule has one old parental DNA strand and one new DNA strand hence semi conservative

replication of DNA.

NB

DNA polymerase cannot catalyze the formation of phosphodiester bonds in the 3’ to 5’ direction and

therefore the 3’ to 5’ end is replicated in short sections, known as akazaki fragments. This is a lagging

strand because its synthesis is slow.

These fragments or sections are joined by the enzyme DNA ligase to form a continuous polynucleotide

chain.

SEMI-CONSERVATIVE REPLICATION OF DNA: The experiment of Meselson and Stahl

They grew E.coli bacteria in a medium containing heavy nitrogen (15N) for many generations so that all the

DNA ware heavy.

They took a known mass of a sample of these bacteria, isolated DNA through centrifuging and put it in a

separating solution, caesium chloride. The DNA band occupied the lower position indicating that all the

strands of these DNA had heavy nitrogen.

They grew the remaining bacteria in a medium containing light nitrogen (14N) for several generations.

(i) In the 1st generation (1st replication)

They grew the remaining bacteria in a medium containing light nitrogen (14N) for one generation.

After this first generation, they took the same known mass of a sample of these bacteria, isolated DNA

through centrifuging and put it in a separating solution, caesium chloride.

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The DNA band occupied the middle position indicating that all the strands of DNA had heavy and light

strands, hence proving semi conservative replication of DNA.

(ii) In the 2nd generation

They grew the remaining bacteria in a medium containing light nitrogen (14N) to get 2nd generation

After this 2nd generation, they took the same known mass of a sample of these bacteria, isolated DNA

through centrifuging and put it in a separating solution, caesium chloride.

The DNA had two bands in the separating solution with equal thickness i.e. a hybrid band of DNA in the

middle position and a light band of DNA near the top.

(iii) In the 3rd generation

They grew the remaining bacteria in a medium containing light nitrogen (14N) to get 3nd generation

After this 3nd generation, they took the same known mass of a sample of these bacteria, isolated DNA

through centrifuging and put it in a separating solution, caesium chloride.

The DNA had two bands in the separating solution i.e. a hybrid band of DNA in the middle position whose

thickness was a third and a light band of DNA near the top whose thickness was two thirds. The ratio of

the light to hybrid band was 6:2 i.e. 3:1

Q. Explain how Meselson and Stahl’s classic experiment supported the theory of semi-conservative

replication and refutes the idea of conservative replication

The experiment showed that after one replication (generation) in a medium containing light nitrogen, the

DNA band occupied the middle position in the separating medium proving that all the DNA molecules had

one strand containing heavy nitrogen and the other strand containing light nitrogen, and this explains semi

conservative replication of DNA.

If there had been conservative replication, they would have found half the DNA molecules containing

heavy nitrogen and the other half containing light nitrogen.

NB

However, in all replications, a parental strand (15N) will always be there, further giving evidence of semi

conservative replication of DNA

Questions

The bacteria in the medium absorbed 15N and used them to synthesize the nitrogenous bases of the

mononucleotides that join to form DNA.

(a) Name a component of DNA that contains nitrogen. (1)

Nitrogenous base

(b) Name three enzymes involved in DNA replication. (3)

DNA helicase

DNA polymerase

DNA ligase

Which enzyme causes nucleotides to join up to form a polynucleotide chain? What type of reaction is this?

The enzyme is DNA polymerase

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The reaction is a condensation reaction

THE GENE AND GENETIC CODE

Genetic code

Genetic code is the sequence of bases (nucleotides) on one strand of DNA that determines sequence of

amino acids in a protein.

Genetic code is a triplet code i.e. a triplet of bases (3 nucleotides).

This triplet of bases codes for one amino acid, a start signal or stop signals.

The sequence of triplet of bases codes for the sequence of amino acids that form a polypeptide, which will

fold up to form a protein.

Why a triplet of bases

There are 20 different types of amino acids

There are 4 different types of bases (ACGT)

(i) If one type of base codes for one type of amino acid, only 4 will be coded for, not 16: 4 1 =4 different

types of amino acids.

(ii) If two different types of bases code for an amino acid, only 16 will be coded for, leaving out 4: 4 2 =16

different types of amino acids.

(iii) If 3 different types of bases code for an amino acid, there will be 64 triplet of bases, which are more

than enough. So, all the 20 different types of amino acids, start signal and stop signals will be coded

for.

So, the genetic code is triplet in nature

The start triplet of bases (start signal) on the DNA strand is TAC

The stop triplets of bases (stop signals) on the DNA strand are ATT, ACT and ATC

The importance of triplet code

Allows for all the 20 different types of amino acids, start and stop signals to be coded for.

Gene

- A gene is a sequence of bases on one strand of DNA which codes for a polypeptide (sequence of amino acids),

or it is also a small section of DNA that codes for a polypeptide chain (chain of amino acids)

- Gene locus is the region on the chromosome where a gene is located.

PROTEIN SYNTHESIS

- This is the making of new proteins

- It takes place on the surface of ribosomes in the cytoplasm.

- However, proteins synthesis (joining of amino acids by peptide bonds on the surface of ribosomes) is controlled

by the DNA in the nucleus.

- So, there is a messenger that carries the genetic information from the DNA to the surface of ribosomes.

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- The messenger is called mRNA. This mRNA is synthesized by the antisense DNA strand in the nucleus in a

process called transcription.

- The DNA cannot leave the nucleus because;

a) It is too large to pass through the nuclear pores

b) It is a master copy that should remain in the nucleus

c) Ribosomes are not in the nucleus.

- The protein synthesis has the following stages;

1. Transcription

2. Post transcription modification

3. Amino acid activation

4. Translation

Transcription in the eukaryotic cells.

a. Definition- This is the synthesis of mRNA by the antisense DNA strand in the nucleus through complementary base pairs. Antisense DNA strand acts as a template to make mRNA

b. Process- DNA helicase breaks down hydrogen bonds between the two strands of the DNA and separate them to

expose their bases. The antisense DNA strand acts as a template to synthesis mRNA Nucleotides bind to complementary nucleotides of the antisense DNA strand by hydrogen bonds RNA polymerase catalysis the formation of phosphodiester bonds between the nucleotides, forming

mRNA. The mRNA detaches from the antisense DNA strand

Post transcription modification

- The mRNA (in eukaryotic cells) has sections called introns that do not code for amino acids, and others called

exons which code for amino acids. Introns are removed and exons joined by ligase enzyme to form a

continuous coding mRNA strand.

- Addition of Guanine (Guanine cap) at the 5’ end that act as a signal to start translation.

- Addition of about 100 adenine molecules (poly A-tail) at the 3’ end which has 2 functions

a) Act as a signal to export mRNA from the nucleus

b) Protect the mRNA from enzyme action

- The modified or mature mRNA leaves the nucleus through the nuclear pore to the surface of ribosomes

- Ribosomes hold together the mRNA, tRNA and enzymes that control protein synthesis

Amino acid activation

When mRNA reaches the ribosome, the smaller sub unit of ribosome hold the mRNA and it holds two codons

at a time hence two tRNA at a time.

This binding of mRNA to ribosome triggers amino acid activation.

Amino acid activation is the binding of amino acids to specific tRNA molecules at the end of 3’

This binding requires; 110

1. An enzyme called amino acyl tRNA synthetase

2. Energy from ATP

Translation

Definition

This is the conversion of the sequence of codons (triplet of bases) on the mRNA into a sequence of amino acids (polypeptide chain), on the surface of ribosomes.The mRNA acts as a template during translation. The amino acids are joined by peptide bonds. These amino acids are carried to the surface of ribosomes by specific tRNA molecules.

Role of molecules during protein synthesis

1. Antisense DNA strand- Acts as a template to synthesize mRNA molecule in the nucleus of a eukaryotic cell.

2. mRNA- This is a copy of the antisense DNA strand formed by transcription in the nucleus.- Carries genetic message in form of codons.

- It moves out of the nucleus to the ribosomes.

- On the surface of ribosomes, it acts as a template for translation.3. tRNA

- It binds to a specific amino acid.-It carries this amino acid to the mRNA on the surface of ribosome for translation.- It therefore ensures correct sequence of amino acids.

4. Ribosomes- it holds together the enzymes, mRNA and tRNA during translation.

Description of terms during protein synthesis;

1. Cistron- The sequence of triplets on a section of DNA used to form a strand of pre-mRNA2. Codon- this is a triplet of bases on the mRNA3. Anti-codon- this is a triplet of bases on the tRNA, that is complementary to the codon on the mRNA.

List the differences between DNA replication and transcription

DNA replication Transcription

1. DNA polymerase catalyzes RNA polymerase catalyzes

2. Both DNA strands act as templates Only one strand ;anti-sense strand/template

strand act as template

3. A pair with T A pair with U

4. Whole DNA molecule replicated A length DNA (gene) is transcribed.

Note

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Template strand or anti-sense strand is the DNA strand that synthesizes mRNA during transcription.

Sense strand /DNA strand that does not synthesize mRNA and is complementary to the template strand or anti

sense strand. However it is an exact copy of the m RNA, the difference being only Adenine and uracil hence it

is called sense strand.

GENE MUTATIONS

- A gene mutation is the change in a base sequence (nucleotide sequence) on the DNA and this gives rise to a

change in amino acid sequence in the protein.

- If mutations occur in reproductive cells, in ovaries and testes, then the gametes (sperm and egg cells) formed

from these reproductive cells will have mutations and can be inherited.

- If mutations occur in other cells they are not inheritable

Substances that can cause mutations are called mutagens and include;

1. Harmful chemicals e.g. nitrous acid

2. Ionizing radiations e.g. gamma rays

Organisms with mutations are called mutants

Types of gene (point) mutations

1. Frame shift gene mutations

This is when there is a change in the entire sequence of the codes/triplet of bases from the region of point of

mutation as a result of insertion or deletion of nucleotides.

2. Non frame shift mutations

- Only one or few of the nucleotides in the gene are altered as a result of substitution of nucleotides.

- This substitution mutation (non-frame shift mutation) may not have any effect on the phenotype because;

(i) It could be a recessive allele that does not express itself phenotypically

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(ii) It could be an intron that is removed during post transcription modification.

(iii) It could be degenerate i.e. several codes code for the same amino acid.

NB: Frame shift mutations have severe effects on polypeptide chains while non-frame shift mutations have mild

effects because usually only amino acid is affected.

How a gene mutation results in a protein that does not function normally

- Gene mutation is the change in a base sequence on the DNA due to insertion, deletion or substitution.

- This gene with different bases is transcribed into mRNA with different codons

- This mRNA is translated into different amino acids in the polypeptide chain/primary structure.

- These amino acids haves different R groups which determine different chemical bonds that in turn give rise to

different shape/structure of protein that cannot function properly or has different functions.

CYSTIC FIBROSIS (CF) AND GENE MUTATION CALLED DELETION

What is CF?

CF is a genetic disorder where gene mutations affect CFTR gene on chromosome no. 7. These mutations give rise to a faulty CFTR gene that codes for a faulty CFTR protein (chloride channel

protein) on the apical membrane of the epithelial cells, which causes accumulation of thick and sticky mucus in the pancreatic duct in the pancreas, airways, oviducts, cervix and sperm ducts.

Describe the normal function of CFTR protein

acts as chloride channel Cl – moves out of cell Binding site for ATP

Briefly describe the common gene mutation that causes CF.

The common one is called DF- 508, whereby the 508th triplet of bases (the CFTR gene consists of 1480 triplet of bases) on the CFTR gene is deleted so that phenylalanine amino acid is not be coded for in the CFTR protein; and this faulty protein will not fold correctly, hence will not allow chloride ions to diffuse from the epithelial cells into the mucus.

Another type of gene mutation affecting CFTR gene is loss of ATP binding site on the CFTR protein. Explain the role of ATP and how lack of this site causes the closure of CFTR protein.

ATP binds to its active site in the CFTR protein; it is hydrolysed to get energy; this energy causes the chloride channel to open.

Lack of ATP means that there will be no energy to open the chloride channel protein (CFTR protein), causing the accumulation of chloride ions in the epithelial cells.

How does CF cause thick and sticky mucus in the airways?

The faulty CFTR protein causes the chloride ions to accumulate in the epithelial cells. Sodium ion channels remain open and allow Na ions to diffuse from the mucus into the epithelial cells. Na and Cl ions in the epithelial cells create osmotic gradient causing water from the mucus to move into

the epithelial cells by osmosis leaving behind thick and sticky mucus.Give reasons why most designed DNA tests for mutations in CF give false negative results.

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CF is caused by many different types of mutations and so any designed DNA tests will detect few mutations and leave out others and therefore the person maybe declared negative for CF, but it is a false negative.

A couple is declared negative for CF. However, they gave birth to a child who is a genetic carrier for CF. Suggest reasons for this.

False negative. This is because the designed DNA tests did not detect other gene mutations, hence a false negative result.

Mutation may have occurred in the egg or sperm cell, after the test was done. Mutation occurs in the zygote.

CF analysis is done in the body cells (diploid cells) and not in the gametes (haploid cells). Suggest reasons for this.

It is easier to obtain body cells. Body cells are genetically similar. Diploid cells have full no. of chromosomes and this allows mutations to be detected from all the

chromosomes; gametes, haploid cells, have half the no. of chromosomes.List 3 human systems affected by CF.

Reproductive Respiratory Digestive

List 3 effects of respiratory CF.

Accumulation of mucus in the airways hence reduced airflow. Reduced gas exchange between the alveoli and the capillaries surrounding them. Lack of energy that causes fatigue Bacterial infection. This is because the mucus containing bacteria cannot be removed from

the airways because cilia have become functionless. Breathing difficulties

Suggest reasons why heart and lung transplant maybe prescribed as a treatment for CF

Due to less oxygen reaching the heart, the heart becomes weak and may trigger heart attack. The lungs get infections and may affect breathing and gas exchange.

Explain why a CF patient has saltier sweat.

In a normal person, the chloride channel proteins in the epithelial cells of the sweat duct in the sweat gland cause Cl ions to diffuse from the sweat in the sweat duct into the sweat gland. This causes sodium ions and water to move in the same way leaving behind little sweat with less Na and Cl.

In the CF patient, Cl ion channel is non-functional, causing accumulation of Cl ions in the sweat in the sweat duct that also attract Na ions and water, so that there is more sweat with a lot of salts.

This is why one of the treatments of CF is to provide salt supplement to CF patients to compensate the lost ones.

What is the role DNAses mucolytics and antibiotics in a CF patient?

Because of bacterial infections, a lot of WBCs move to the infected areas of the lungs but they die in this thick and sticky mucus releasing their DNA. These DNA molecules increase the stickiness of

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the mucus. So, DNAses digest/breaks down DNA to reduce the stickiness of the mucus in the airways.

Mucolytics are drugs that make the mucus more runny and so easier to move i.e. dilate the airways

and make the mucus more liquid.

Antibiotics kill bacteria in the thick and sticky mucus to prevent bacterial infection in the lungs.

CF patients take a tablet before they take a meal and this tablet contains enzymes. Write the names of these enzymes and suggest a reason why they are taking them.

These enzymes are; Trypsin, Lipase and Amylase. This is because the thick and sticky mucus blocks pancreatic duct in the pancreas so that these

enzymes do not reach the duodenum.

Explain why CF patients take insulin?

They are diabetic. This is because blockage of pancreatic duct in the pancreas causes the activated enzymes especially

trypsin to digest beta cells in the pancreas that produce insulin.

Cystic fibrosis (CF) is an inherited disease.(i) Explain briefly how two parents who do not have CF may have a child with CF.

parents, heterozygous/carriers ; CF allele recessive ; CF child homozygous recessive ;

(ii) Describe two ways in which CF affects the lungs. thick/sticky/dehydrated, mucus produced mucus not moved effectively by cilia/mucus accumulates reduced gaseous exchange/longer diffusion pathway difficulty in breathing infections/(mucus) traps bacteria lungs are scarred

(b) One potential way of treating CF is by using gene therapy.(i) Outline, with reference to CF, what is meant by gene therapy.

alters genotype insert, dominant/normal, allele into, affected/appropriate, cells ; use of vector/named vector ; ref. recombinant DNA ;

(ii) Describe one possible advantage and one possible disadvantage of using gene therapy to treat CF.advantage

treats cause not symptoms ; no, physiotherapy/antibiotics/etc, needed ; less time consuming than others treatments ;

disadvantage effects only last for a few days (at present)/low uptake by target cells ;

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only target lung cells (at present) ; side effects ;

THE EFFECT OF CF

1. Gas exchange (How CF affects the lungs)

thick/sticky/dehydrated, mucus not moved effectively by cilia/mucus accumulates reduced gaseous exchange/longer diffusion pathway difficulty in breathing infections/(mucus) traps bacteria lungs are scarred

2. Digestion

- Mucus blocks the pancreatic duct ion the pancreas, so digestive enzymes can’t reach the duodenum (small

intestine) and food is not properly digested. This leads to tiredness and difficulty in gaining weight – this is due

to malnutrition

- Enzymes trapped within the pancreas cause fibrosed cysts (swellings) and damage to insulin producing cells (-

cells), leading to diabetes.

3. Reproduction

- In women, mucus can block the cervix preventing entry of sperm hence infertility

- In men, the vas deferens (sperm ducts) is blocked with mucus so sperm cannot leave the epididymis

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Questions

1. Make a take to show which tubes are blocked and what problems this leads to

Tube blocked Problem

1. Bronchioles Less fresh air gets to alveoli leading to shortness of breath

2. Pancreatic duct Digestive enzymes (amylose, trypsin, and lipase) don’t get into

duodenum. This leads to inefficient food digestion hence

malnutrition. It also leads to diabetes.

3. Cervix Sperm cannot pass into uterus hence no conception leading to

infertility

4. Vas deferens Sperm cannot move to urethra, leading to infertility

What does CFTR not do properly when it is a product of a mutated allele and why does this make mucus

sticky? It does not allow Cl- ions out of the epithelial cells and it does not inhibit the Na+ channels. Both of these

mean that the osmotic gradient is into the cell rather than out so, water is withdrawn from the mucus outside the

cell making it too sticky.

Make a table to show the effects of CF and how they are brought about

Effect of CF sufferer Origin of effect

1. Breathing problems - Bronchioles blocked with sticky mucus stopping

entry of fresh air into alveoli

- Alveoli wall lined with thick mucus reducing diffusion

2. Lung infection - Sticky mucus traps bacteria which multiply and cause

infection

3. Poor weigh gain - Blocked pancreatic duct prevent digestive enzymes

getting into smaller intestines hence inefficient food

digestion

4. Diabetes - Due to blocked pancreatic duct, enzymes destroy

- - cells that produce insulin

5. Infertility in woman - Mucus blocks cervix hence no passage of sperm

6. Infertility is men - Sperm duct blocked by mucus

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GENETICS

- This is the study of heredity and variation

- It deals with the transmission of genes from parents to offspring.

- The terms used are:

1. Gene

- Small section of DNA that codes for a polypeptide or sequence of bases on the DNA strand that codes for a

polypeptide (sequence of amino acids)

- It occupies a region on the chromosome called gene locus

- Usually a gene has two forms /alleles

2. Allele

- One of the alternative forms of a gene/different forms of a gene

- In a diploid cell, there are usually 2 alleles of any 1gene (1 from each parent which occupy a gene locus)

3. Phenotype

- This is the outward expression of the organism

- It is determined by the inherited alleles, environment, or interactions of the two.

- It is always expressed in words e.g. tall, short, green, black

4. Genotype

- This is the alleles of an organism i.e. it is the genetic composition of an organism

- It is expressed in both words and letters

Word Letters

Homozygous dominant for height TT

Heterozygous for height Tt

Homozygous recessive for height tt

5. Recessive

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- This is an allele of a gene that does not express itself in presence of a dominant allele and only expresses itself

in homozygous state e.g tt, bb, dd

6. Dominant

- This is an allele of a gene that always expresses itself in both heterozygous and homozygous condition

TT Tt

Tall

7. Homozygous

- Condition where the 2 alleles of a gene are identical e.g. TT, tt

- An organism whose 2 alleles of a gene for a particular characteristic are identical is called homozygote.

- Homozygotes breed true when crossed with genetically identical organisms

8. Heterozygous

- Condition where the 2 alleles of a gene are not identical e.g. Tt, Bb

- An organism whose 2 alleles of a gene for a particular characterstic are not identical is called heterozygote

9. Monohybrid inheritance

This is the transmission of 1 gene that codes for 1 polypeptide that determines one characteristic.

Monohybrid crosses

1. Pea height – dwarfnes is recessive to tallness

Parental phenotypes Tall x dwarf

Parental Genotypes TT x tt

Parental Gametes (T) (T) (t) (t)

F1 genotypes Tt Tt Tt Tt

F1 phenotypes all are tall

F1 x F1

Parental phenotypes Tall x Tall

Parental Genotype Tt x Tt

Parental Gametes (T) (t) (T) (t)

F2 genotypes TT Tt Tt tt

F2 phenotypes tall tall tall dwarf

F2 Phenotypic ratio 3:1

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2. seed morphology – wrinkled in recessive to round

Parental phenotyeps round x wrinkled

Parental Genotype RR x rr

Parental Gametes (R) (R) (r) (r)

F1 genotypes Rr Rr Rr Rr

F1 phenotypes All are round

F1 x F1

Parental phenotypes Round x Round

Parental Genotype Rr x Rr

Parental Gametes (R) (r) (R) (r)

F2 genotypes RR Rr Rr rr

F2 phenotypes Round round round wrinkled

F2 phenotypes ratio 3: 1

3. In human genetics, it is not ethically accepted to set up crosses like in plants. The inheritance of characteristics

in humans is studied by looking at natural crosses and the production of offspring using genetic pedigree diagrams.

Genetic pedigree (family tree) is a diagram of family relationships that uses symbols to represent people and lines

to represent genetic relationships. Pedigrees are usually used to determine the mode of inheritance (dominant,

recessive etc) of genetic diseases

In a pedigree

(i) Squares represent males

(ii) Circles represent females

(iii) Horizontal lines connecting a male and female represent mating.

(iv) Vertical lines extending downwards from a couple represent their children

a) Cystic fibrosis

The disorder is caused by a recessive allele

Parental phenotypes normal x normal

Parental Genotype Ff x Ff

Parental Gametes (F) (f) (F) (f)

F1 genotypes FF Ff Ff ff

F1 phenotypes Normal normal normal : cf

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NB

The parents are genetic carriers. A carrier is an individual with a recessive allele for the condition and so does not

show the condition but can pass on the allele to the next generation.

From the above, the heterozygous parents for CF, have 25% chance of having a child with CF

b) Albinism

- This condition is caused by a recessive allele

- Natural melanin pigment of the skin, eyes and hair does not form

- A mutant recessive allele prevents the formation of a normal tyrosinase in melanocytes (pigment forming cells)

hence no formation of melanin

- 2 normal parents give birth to an albino. Show this is a genetic diagram.

Parental phenotypes Normal x Normal

Parental Genotypes Aa x Aa

Parental Gametes (A) (a) (A) (a)

F1 genotypes AA Aa Aa aa

F1 phenotypes 3 normal : 1 albino

F1 Phenotypic ratio 3:1

Genetic pedigree diagram for albinism

Question 121

1. Is albinism caused by recessive/dominant allele?

- It is caused by recessive allele

- Because parent 1 and 2 do not show the disorder yet they have a child (4) with the condition

- If it was a dominant allele, the parents would show it

2. Using A and a for 2 alleles, write genotypes for all these people

1. Aa

2. Aa

3. AA or Aa

4. aa

5. Aa

6. aa

7. Aa

8. Aa

9. aa

3. The pedigree below shows the inheritance of CF in one family

a) Give the name of a female who is homozygous for the C.F gene

b) Is CF caused by a dominant allele /recessive allele? Explain

it is a recessive allele this is because the parents do not show a disorder (Jane and Peter) hence not dominant. In

addition they have a child with CF (priya)

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c) Give the name of a more who is heterozygous for a CF gene

Peter and Samir

d) If Fiona and samir had a 3rd child, state the probability that the 3rd child could have Cf

Parental genotype Ff x Ff

Parental Gametes (F) (f) x (F) (f)

F1 genotype FF Ff Ff ff

Therefore probability = 25% for C.F

e) From the diagram give evidence that shows that CF is caused by an allele that is autosomal. This autosomal

because it affects both males and female hence, it is not a sex linked allele.

f) Suggest how an individual with the heterozygous genotype for this disorder could be identified.

1. Gene probe

2. Identification of base sequences of a gene /allele

c) Thelassaemia

- Caused by recessive allele

- Is an inherited autosomal recessive blood disease that prevents the formation of either or hemoglobin

chains.

- This cause the formation of abnormal haemoglobin molecule causing symptoms of anaemia – fatigue and lack

of energy due to insufficient oxygen in the blood (sickle cell anameia *qualitative) is not the same as the

thalassaemia (quantitative)

- So there are two types of thalassaemia:-

(i)

(ii)

- They are both caused by a recessive allele

- Thalassaemia

- Its inheritance involved 4 genes on chromosomes 16, hence shows polygenic inheritance

- thalassaemia is due to deletion of/or more of these genes

- All 4 genes can be deleted which can be fatal

Thalassaemia

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- Caused by mutations in the hemoglobin gene on chromosome II

- Are 2 types

(i) Thalassaemia minor

- The person with this is heterozygous for the condition, hence has mild anemia.

(ii) Thalassaemia major (Cooley’s anemia)

- The child is homozygous for thalasaemia

- Chains of hemoglobin are not made at all hence very serious disease

Thalasaemia and malaria

- Carries for this condition have protection against malaria, hence the condition contains a selective survival

advantage on carries hence perpetuating the mutation.

- So in malaria prone zones the highest pupation is that of carriers.

- In thalassaemia, carriers can be normal or suffer from mild anemia hence the 2 alleles (dominant and recessive)

affect the prototype. This is a case of incomplete dominance.

TREATMENT OF CYSTIC FIBROSIS

CF is a life threatening condition.

At the moment there are no cures for CF.

Current treatment aim to reduce the symptoms and allow the body systems to work as effectively as

possible

There is a range of treatments that combat different symptoms:

1. Physiotherapy

It loosens and removes the thick, sticky mucus from the lungs so that:

a) There is improved flow of air into and out of the lungs.

b) There is more surface area available for gaseous exchange (alveoli).

c) There is less risk of infection because sticky mucus has bacteria.

Devices for physiotherapy include:

a) Flutter

b) Positive Expiratory Pressure (PEP) Valve

c) ThAIRapy bronchial drainage system

2. Diet

o Eat a careful balanced diet.

o Eat more than other people to make up for what they cannot digest.

o Adults with CF need more high energy foods such as high fat and high carbohydrate foods. This is to

keep them warm as cold can cause more mucus production.

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o An adult with CF needs twice as much protein as someone unaffected by the condition.

o Some may need salt supplements. This is because a lot of salt is lost in sweat because in sweat ducts

the CFTR protein works in opposite direction to the way it works in mucus producing cells i.e. salt is

normally reabsorbed from sweat using the CFTR channel; with CF this does not function; so the salt

is not absorbed making saltier sweat.

3. Digestive enzymes

To help overcome the effect of the blocked pancreatic duct, people with CF may take enzymes when they

have a meal. These enzymes include the trypsin, amylase and lipase, and help to replace the missing

pancreatic enzymes so that more of the food can be digested.

4. Drug therapies (Medication)

Combination of drugs needed for CF varies from person to person and overtime for an individual. These drugs

include:

A. Antibiotics : aerosols (inhalers) are used to breathe them deep into the lungs to destroy bacteria.

B. Vaccines : two vaccines are very important to prevent the patients against:

Flu Virus

Pneumonia

Flu and pneumonia add mucus hence worsening the condition.

C. Mucolytics : these are drugs to make the mucus more runny and so easier to move. i.e. dilate the airways

and make the mucus more liquid.

D. Asthma drugs : e.g. Salbutamol and steroids: these are used to dilate the airways and also reduce

inflammation in the lungs.

E. DNAase enzymes: infection of the lungs leads to the accumulation of white blood cells in the mucus. The

breakdown of these white blood cells release DNA which adds to the stickiness of the mucus. DNAase

enzymes can be inhaled using a nebulizer to breakdown the DNA so the mucus is thinner and easier to

clear from the lungs through coughing.

F. Insulin: If CF leads to diabetes, insulin is taken to control the blood sugar concentration.

5. Transplant surgery (Heart and Lung Transplant)

Due to severe damage of these organs, lungs and heart transplant remains the option.

However, after transplant immunosuppressant drugs should be taken throughout the rest of the life to

prevent rejection of the new tissue by the body. This suppresses the immune system, making it harder to

fight infection.

However, people with CF who have transplants, usually do very well.

6. Infertility treatment

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Women can get children through fertility treatment as In vitro Fertilisation (IVF).

For men, sperm are taken from their testes and fertilize eggs in vitro (outside the body). The resulting

embryos are then returned to the mother’s uterus to develop normally.

7. Gene therapy- This is the transfer of a normal gene/allele to a target cell so that it is expressed to produce a

functional protein.

GENE THERAPY

Why is gene therapy possible in treating CF Cystic fibrosis is caused by a recessive allele of a single gene, hence a good candidate

for gene therapy.

This is one of the treatments of CF and other genetic conditions.

This is the transfer of a normal gene to a target cell so that it is expressed to produce a functional

protein.

The requirements for gene therapy are:-

1. Restriction Enzymes/ Restriction Endonucleases

2. DNA Ligases

3. Vectors

RESTRICTION ENZYMES

They have 2 functions where they cut DNA at restricted sites of specific bases.

1. They cut out the normal gene from the DNA in a staggered manner to get sticky ends which have

complementary bases to the bases of sticky ends of the vector.

2. They cut open a vector in a staggered manner to expose sticky ends that have bases complementary to

those of the sticky ends of the gene.

DNA LIGASE

It catalyses the formation of Hydrogen bonds between the complementary bases of the sticky ends of both

the gene and the vector, forming a recombinant DNA (rDNA).

VECTORS

These are molecules that carry normal genes to the target cells.

There are 3 types of vectors:-

1. Viral DNA – It is the best to transfer the normal gene to the animal target cells. The genes that cause

disease in this DNA are removed before it is used as a vector. However, its use as a vector has side

effects in humans:-

(a) Immune Reaction

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(b) Headache

(c) Fever

(d) Fatigue

(e) Raised heart rate

2. Plasmids – These are small circular DNA found in some bacteria. They are used as a vector. They are

the best to transfer the normal gene to the target bacterial cells and the plant cells. If they have to be

used to transfer the normal gene to animal cells, they must be used with another vector known as

LIPOSOME.

3. Liposomes – These are vesicles that consist of phospholipid bilayer. This layer is compatible with the

animal phopholipid bilayer of the plasma membrane, hence they can easily fuse.

THE PROCESS OF GENE THERAPY

OUTLINE GENE THERAPY FOR CF

1. Restriction enzyme cuts out the normal gene from the DNA.

2. The same restriction enzyme cuts open a plasmid.

3. The gene is introduced into the plasmid using DNA ligase to join them using hydrogen bonds, forming

rDNA.

4. The rDNA is inserted into the liposome forming liposome-rDNA complex.

5. The complexes are taken as nasal spray to the target cells (epithelial cells) in the lungs.

6. Inside the epithelial cells the gene is expressed (Transcription and Translation) forming a functional CFTR

protein.

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PROBLEMS WITH THE CURRENT GENE THERAPY FOR CF.

1. Only about 25% of the normal chloride transport is restored.

2. The effect is temporary i.e. up to 2 weeks. This is because when the epithelial cells with the gene die, the

replacement cells have no gene.

3. Use of viruses as a vector can cause the following side effects:-

(a) Immune reaction

(b) Headache

(c) Fever

(d) Fatigue

(e) Raised heart rate

4. Delivery is very inefficient especially with liposomes. Only about 1 out of 1000 genes gets into the

epithelial cells.

TYPES OF GENE THERAPY

1. SOMATIC GENE THERAPY

This is the introduction of a normal gene into the body cell.

It is permitted in many countries because:-

(a) It only affects target body cells

(b) It is not inheritable

(c) It cannot be misused to make designer babies

(d) Future generations are not needed to give consent

2. GERM-LINE GENE THERAPY

This is the introduction of a normal gene into a zygote in IVF (In vitro Fertilisation).

This is illegal for the following reasons:-

a) It affects all the body cells

b) It is inheritable

c) Future generations are unable to give consent

d) May be misused to create designer babies

AVOIDANCE AND EARLY TREATMENT

As genetic disorders have no cure, potential parents have the following options:-

(a) Avoid having a child with such a condition

(b) Start treatment immediately after birth which improves health in later years.

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These options involve Genetic Screening/ Testing

GENETIC SCREENING

This is the identification of genetic carriers by the identification of a faulty allele in the DNA of any cells.

A genetic carrier is an individual with a recessive allele for the condition and thus does not express the

condition but can pass on this allele to the offspring.

Examples of Genetic Screening are:-

1. Genetic Screening of new born babies

2. Genetic screening of adults

3. Pre-natal Genetic Screening

4. Pre-implantation Genetic Diagnosis (PIGD)

GENETIC SCREENING OF NEW BORN BABIES

These new born babies are tested for defective alleles for genetic disorders such as CF.

The blood sample is taken and the defective genes identified.

This will help in the introduction of early treatment, in case they are sick, in terms medicine and nutrition

which improves health in later years.

GENETIC SCREENING OF ADULTS TO IDENTIFY CARRIERS

This falls into 3 categories:-

a) If one member of a family is born with CF, the other members of the family need genetic screening.

b) If one partner in a couple has been detected to be a carrier then the other partner needs genetic

screening because in case of CF which is caused by a recessive allele, there is a quarter chance that the

child will have the disease. So genetic screening helps the couple to make informed decisions.

c) A person can go for genetic screening irrespective of the above two reasons.

ADVANTAGES OF GENETIC SCREENING OF ADULTS

(a) To make informed decision such as whether or not to have a child.

(b) Peace of mind.

DISADVANTAGES OF GENETIC SCREENING OF ADULTS

1. Insurance problems-termination of insurance cover or lack of insurance cover.

2. Difficulties in employment-loss of employment or lack of employment.

3. Difficult to get a partner to marry

4. Social stigma

5. False positives-shows you have the condition yet you don’t have.

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6. False negatives-shows you don’t have the condition yet you have it.

7. Confidentiality of results

Question (Jan 2011)

Cystic fibrosis is a life-threatening condition that can affect many different parts of

the body. It is a recessive genetic trait. Genetic screening can be used to test for the

presence of recessive alleles. A person found to possess a recessive allele is called a carrier.

(a) Suggest why cells from mouth swabs or blood samples are used rather than

gametes.

These cells are easy to collect

Large number of cells can be collected

Being diploid cells, they contain all the 46 chromosomes

These cells are genetically identical, i.e., have the same alleles

Any recessive allele or mutated C.F gene will be present in them

If gametes are used they may not contain all the mutated CF gene because they are haploid( 23

chromosomes)

(b) Explain why it is necessary to test for several different recessive alleles in the

screening for cystic fibrosis.

Cystic fibrosis results from one of a number of different gene mutations.

So, testing for only one will miss other recessive alleles.

(c) In the risk analysis shown, if neither partner is a carrier then it is considered

that the chance of having a child with cystic fibrosis is low. Explain why the

probability of having a child with cystic fibrosis is low and not zero.

False negatives

Screening programme does not test for all possible mutations that can cause CF

Mutation may occur in the formation of gametes

Mutation may occur after fertilisation.

(d) In the risk analysis shown, if one of the partners is found to be a carrier then screening for cystic fibrosis may be

offered to other family members. Explain why this screening is offered to other family members.

Any other family member could be a carrier.

informed choices can be made about having children (if they know that they

are carriers) ;

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PRENATAL GENETIC SCREENING

This involves genetic testing of embryos or foetuses. It’s divided into two:

a) Chorionic Villus Sampling (CVS)

b) Amniocentesis

HOW CAN CVS BE USED TO DETECT CF

Placental tissue is removed from the uterus of the mother within 8 – 10 weeks of pregnancy using a

syringe.

Fetal cells are present in the placental tissue.

DNA is analyzed in those fetal cells through Karyotyping DNA analysis to detect defective genes.

ADVANTAGES OF CVS

1. If termination of pregnancy is needed it’s less traumatic for the mother as this method is carried out early in

the pregnancy.

2. Results are available immediately compared to amniocentesis.

DISADVANTAGES OF CVS

1. Risk of miscarriage due to procedure.

2. Risk of harm to foetus due to procedure.

3. Defective X chromosomes can’t be detected at this early stage as X chromosomes are inactive in fetal

placental cells.

4. False positives

5. False negatives.

HOW AMNIOCENTESIS CAN BE USED TO DETECT CF

About 20cm3 of amniotic fluid is removed from the amniotic sac of the mother using a syringe within 14 –

16 weeks of pregnancy.

This amniotic fluid has fetal cells that are needed.

These cells are cultured for 2 – 3 weeks.

DNA is analysed through Karyotyping DNA analysis to detect defective genes.

ADVANTAGES OF AMNIOCENTESIS

1. Less risk of miscarriage compared to CVS.

2. Defects in X chromosomes can be detected.

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DISADVANTAGES OF AMNIOCENTESIS

1. Carried out late in pregnancy so abortion is more traumatic.

2. Results aren’t available until 2 – 3 weeks later causing more trauma and anxiety.

3. Risk of miscarriage due to procedure.

4. Harm to foetus due to procedure.

5. False positives

6. False negatives.

WHY IS AMNIOCENTESIS STILL A NECESSARY OPTION

1. If someone does not realise that they are pregnant till later.

2. Risk of genetic disease is not recognised till later into the pregnancy.

3. Low levels of miscarriage.

4. Can detect defective genes in X chromosome.

MAKING THE RIGHT DECISION ON PRENATAL SCREENING.

There are factors to be considered when deciding what is best in relation to prenatal screening. These are:-

1. Harm to the foetus with subsequent health issues.

2. Right to life of the foetus.

3. False positives

4. False negatives.

5. Risk of miscarriage whether the foetus is healthy or not.

6. The cost of bringing up a baby with the condition.

7. Mental and emotional issues surrounding the birth of a child with the condition.

BENEFITS TO A PREGNANT WOMAN IF PRENATAL TESTING IS DONE

1. Peace of mind.

2. Preparation for treatment.

3. Gives information about abnormalities in foetus.

4. To make informed decisions, i.e. whether to terminate the baby or not.

RISKS TO PREGNANT WOMEN IF PRENATAL TESTING IS DONE

1. Possibility of miscarriage whether foetus is healthy or not.

2. Harm to foetus with subsequent health issues.

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3. Trauma in case of termination.

4. False positives –lead to wrong decisions, e.g. Abortion.

5. False negatives-lead to wrong decisions e.g. giving birth to a child with the condition.

PIGD (PRE-IMPLANTATION GENETIC DIAGNOSIS)

This is genetic screening of embryos created through IVF to see if they carry faulty alleles so that the

embryo that does not have faulty alleles is implanted into the woman.

After cell division through IVF, when the embryo is 8 – 16 cells, a single cell is removed without harming

the embryo for DNA analysis to find out if there is a faulty/defective allele. The embryo that does not have

faulty allele is implanted into the woman.

ADVANTAGES OF PIGD

1. Can take place before woman is pregnant hence no miscarriage or termination of pregnancy.

2. Involves IVF hence one is sure that the baby is free of disease not even a carrier.

DISADVANTAGES OF PIGD

1. Very expensive.

2. Quite unreliable.

3. False positives – Hence embryo destroyed. Some people consider it as a potential human being. So, it is

unethical to destroy it.

4. False negatives- Hence abnormality found later.

5. Harm to the embryo with subsequent health issues.

6. Can be misused to come up with designer babies.

7. Spare embryos can be used in stem cell research which some people consider unethical ( murder of a

potential human).

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