The macro-molecules of life

What are the main components of our diet?

The key components life are carbon-based macromolecules

• Carbohydrates• Lipids• Proteins• (Nucleic Acids –

GENETICS)

These large macromolecules may consist of thousands of

covalently bonded atoms

How big is a macromolecule?

How big is a macromolecule?

Where is carbon on the periodic table?

Carbon has 4 valence electrons

Therefore it can have bond with up to 4 other elements.

Monomer units join together via CONDENSATION REACTIONS

• Monomers are connected by reactions in which two molecules are covalently bonded together through the loss of a water molecule

• This reaction is called a condensation (dehydration) reaction

Breaking Down a Polymer: Hydrolysis

Bonds between monomers are broken by the addition of water molecules

Carbohydrates: Sugars, Starches, Fibre

Where do carbohydrates come from?

Mainly from PLANTS: animals store very little

carbohydrate (as glycogen) in the

body

Why do we need carbohydrates?

Why do we need carbohydrates?

• Instant energy: 17 kJ/g of soluble sugar: glucose

• Stored energy: Starch (plants)/ Glycogen(animals)

• Structure: Cellulose (plant cell walls), Chitin (insect exoskeleton)

What are carbohydrates made of?

3 kinds of atoms: carbon, hydrogen, oxygen [CA

(H2OB)

Different kinds of sugars

Simple (reducing) sugars: Monosaccharides

• All have the chemical composition (C6 H12 O6)

• Glucose – respiratory substrate

• Galactose (milk sugar)• Fructose (fruit sugar)• Small• Sweet • soluble

Complex sugars: Disaccharides

• Small• Soluble• sweet

Complex sugars: Disaccharides

Disaccharide Plant/Animal Functions/Uses

Sucrose Plant Stable, unreactive, transports glucose

around phloem

Lactose animal Hydrolysed by lactase in intestinal villae for easy

absorption

Maltose animal Dimer of glucose broken down by digestion

Polysaccharides: LARGE carbohydrates

• Insoluble• Not sweet

• Used for energy storage and plant,

fungal cell wall structure

Energy Storage Polysaccharides: Starch

Energy storage in plants: easily converted into glucose, and vice versa

Energy Storage Polysaccharides: Glycogen

Found in animals, stored in liver and muscle cells. Extensively branched

• In humans, glycogen banks are SMALL, do not last longer than a day

Structural Polysaccharides: Cellulose

• major component of plant cell walls• Cellulose forms straight unbranched chains• Because of the different structure, very few

organisms have the enzymes necessary to break down cellulose

• A very strong and resistant “insoluble fiber”

Solubility of carbohydrates in water

• Small carbohydrates (simple sugars and disaccharides) are soluble in water

• Complex polysaccharides are often insoluble in water – cellulose, fibre

Testing for sugars: Benedict’s solution

All simple sugars (and some complex, including maltose)

will reduce blue copper salts to a red

colour

Testing for starch: Iodine solution

Brown iodine solution turns blue-

black in the presence of starch

Fats

What are the sources of fat in our diet?

Animal FatsAdipose tissueMilk fatFish oils

Plant oilsOils stored in plant seeds as a store of energy for germination

Why do we need fats?

Fats Serve Many Functions• Energy storage: store twice as

many calories/gram as carbohydrates; 36 kJ/g

• Protection of vital organs• Insulation • Cell membrane structure and

function• Lipid hormones (based on

cholesterol) are used as chemical messengers

Fats (triacyglycerols or triglycerides)

Large molecules created by condensation

reactions between glycerol and 3 fatty

mainly composed of carbon and hydrogen (with a small number

of oxygen atoms)

Saturated or Unsaturated Fatty Acids

Stearic acidSolid at room tempSATURATED

Oleic acidLiquid at room tempUNSATURATED

Saturated and Unsaturated Fatty Acids

Saturated fatty acids• have no double bonds

between carbons• tend to be solid at room

temperature• linked to cardiovascular

disease• are commonly produced

by animals• Examples: butter and lard

Unsaturated fatty acids• have some carbon double

bonds resulting in kinks• tend to be liquids at

room temperature• are commonly produced

by plants• examples are olive and

corn oils

15

What differentiates a saturated from an unsaturated fatty acid?

• Saturated/unsaturated

Are fats soluble in water?

• Of course not!

Key fats in life:Steroids• Steroid hormones are synthesised in the

adrenal glands and the sex organs.• They include sex hormones: testosterone,

oestrogen, progesterone and stress hormones (cortisol)

• They are involved in metabolism, sexual function, inflammation and the immune response

• They are able to diffuse easily through the phospholipid cell membrane into cells

Key fats in life: phospholipids• Phospholipids have only

2 fatty acids. The third space is filled with a phosphate group.

• Phospholipids are ampipathic because they have a negatively charged “head” which is hydrophilic and a non-polar “tail” which is hydrophobic

Cholesterol• Cholesterol is a steroid

which is a common component of animal cell membranes keeping them fluid

• Many hormones including human sex hormones (oestrogen, progesterone, testosterone) are made of steroids: progesterone, testosterone, oestrogen etc

Testing for fat: The emulsion test

This test is used to test for the presence of lipids in a substance.• Lipids are soluble in ethanol but

insoluble in water.• The substance is first dissolved

in ethanol, then mixed with water

• If lipid (fat) is present, then it will precipitate to the top of the solution as an emulsion

Emulsion Test: Procedure1. Add the food sample to

ethanol, shake well.2. Allow to settle in a test tube

rack for 2 minutes for food to dissolve in ethanol.

3. Empty any clear liquid into a test tube containing distilled H2O.

• A milky-white emulsion is a positive result: lipid is present.

• If the mixture remains clear, there are no fats present in the sample

• Lipids are insoluble in water and soluble in ethanol (an alcohol).

• After lipids have been dissolved in ethanol and then added to H2O, they will form tiny dispersed droplets in the water. This is called an emulsion.

• These droplets scatter light as it passes through the water so it appears white and cloudy.

Proteins

Where do proteins come from?PLANTS and

ANIMALS

Why do we need proteins?

Why do we need proteins?• Growth and repair of new cells• Movement – skeletal and heart

muscle• Repair• Communication- hormones• Enzyme function• Cell membrane function (channel

and receptor proteins)• Immune response to infection

(antibodies)

• Energy: 17 kJ/g

• 50% of the dry mass of any cell is protein

• >10,000 different proteins

• The most sophisticated, complex 3-dimensional

structures

What are proteins made of?

• several kinds of atoms: carbon, hydrogen, oxygen, nitrogen, sulphur

• Proteins are polymers of amino acid monomers

• There are many different types of proteins• Key types include STRUCTURAL proteins

and FIBROUS proteins

Structural (fibrous) proteins

• Water insoluble• VERY tough, may also be

supple or stretchySilk: cocoons and webs Keratin: hair, horns, skin, nails, wool, beaksCollagen: tendons and ligamentscontractile proteins in muscle

Globular proteins

• Water soluble• Enzymes• hormones (insulin)• Transport: haemoglobin)• Immune function:

immunoglobulins

Globular proteins:Transport proteins

Haemoglobin, myoglobin: transport of essential substances (oxygen, carbon dioxide)Myoglobin was the first protein to be thoroughly described

Amino Acid (Monomers)Amino acid structure:

NH3 - C - COOH

Amino acids differ due to the R (functional) group

The structure of the R-group determines the chemical properties of the amino acid

20 Amino Acids

Amino Acids link together to form polypeptides

• 2 Amino Acids form a covalent bond, called a PEPTIDE BOND,through a condensation reaction to form a dipeptide

• Multiple amino acids can bond to each other one at a time, forming a long chain called a POLYPEPTIDE

Peptide Bonds – link amino acids

Proteins are folded into unique shapes

• The marvellous shapes of proteins• form the Protein data bank• Beautiful proteins…

Testing for proteins: Biuret’s Test

• Uses potassium hyroxide and copper

sulphate solution mixed together

• The deeper the purple colour, the

more protein present

Testing for protein: Biuret’s Test

Food tests are often used in combination

Carbohydrates Fats (lipids) Proteins

Elements they contain C,H,O C,H,O C,H,O,N, S

Individual units Simple sugars (monosaccharides)

Glycerol and fatty acids

Amino acids

Solubility in water Simple sugars and small sugars are

soluble. Fibre can be insoluble

insoluble Globular proteins are soluble/fibrous

proteins are insoluble

Why organisms need them

Easily available energy (17 kJ/g)

Structural carbohydrates:

cellulose and chitinStorage : starch and

glycogn

Energy storage (39 kJ/g)

Insulation and protection

Cell membranesSteroid hormones

Movement-musclesGrowth and repair

EnzymesImmune function:

antibodiesEnergy

HormonesCel membrane

receptorsFoods that contain

themPlants only: breads, fruits, rice, wheat

Animal and plant sources

Animal and plant sources