What are macromolecules? Give examples. Solution 1: Question 2

Class XI Chapter 9 – Biomolecules Biology

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Book Name: NCERT Solutions

Question 1:

What are macromolecules? Give examples.

Solution 1: Chemical compounds, which are found in the acid insoluble fraction are called macromolecules

or biomacromolecules. For example, proteins, lipids and carbohydrate, etc.

Question 2:

Illustrate a glycosidic, peptide and a phosphodiester bond.

Solution 2:

Glycosidic Bond glycosidic is a type of functional group that joins a carbohydrate (sugar)

molecule to another group, which may or may not be another carbohydrate.

Peptide Bond A peptide bond (amide bond) is a chemical bond formed between two molecules

when the carboxyl group of one molecule reacts with the amine group of the other molecule,

thereby releasing a molecule of water (H2O).

Phosphodiester Bond A

Phosphodiester bond is a group of strong covalent bonds between a phosphate group and two

other molecules over two ester bonds. In DNA and RNA the phosphodiester bond is the linkage

between the 3’ carbon atom of one sugar molecule and the 5’ carbon of another deoxyribose in

DNA and ribose in RNA.


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Question 3:

What is meant by tertiary structure of proteins?

Solution 3:

Tertiary Structure of Proteins Tertiary structure of proteins is generally stabilized by non-local

interactions, most commonly the formation of a hydrophobia core, but also through salt bridges,

hydrogen bonds, disulphide bonds and even post-translational modifications. The term ‘tertiary

structure’ is often used as synonymous with the term fold. The tertiary structure is what controls

the basic function of the protein.

Question 4:

Find and write down structures of 10 interesting small molecular weight biomolecules. Find

there is any industry which manufactures the compounds by isolation. Find out who are the

buyers.

Solution 4:


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Molecular weight There are many industries who make these biomolecules now-a-days these

biomolecules are used in many drugs, injections, medicines, food preparation so are used by

several people.

Question 5:

Proteins have primary structure. If you are given a method to know which amino acid is at either

of the two termini (ends) of a protein, can you connect this information to purity or homogeneity

of a protein?

Solution 5:

The sequence of amino acids, i.e., the positional information in a protein which is the first amino

acid, which is second and so on is called the primary structure of a protein. The first amino acid

is also called as N-terminal amino acid. The last amino acid is called the C-terminal amino acid.

Yes, we can connect this information to purity or homogeneity of a protein. Based on number

of amino and carboxyl groups, there are acidic (e.g., glutamic acid), basic (lysine) and neutral

(valine) amino acids, proteins may be acidic, basic and neutral.

Question 6:

Find out and make a list of proteins used as therapeutic agents. Find other applications of

proteins (e.g., cosmetics etc.)

Solution 6:

Some Proteins and their Functions

Protein Functions

Collagen Intercellular ground substance

Trypsin Enzyme

Insulin Hormone

Antibody Fights infectious agents

Receptor Sensory reception (smell, taste, hormone, etc.)

GLUT-4 Enables glucose transport into cells

Question 7:

Explain the composition of triglyceride?

Solution 7:

Triglycerides are composed of two types of molecules, i.e., glycerol (3 carbon molecules) and

fatty acids which attach to the glycerol at the alcohol unit. The following is a structural

representation of a triglyceride at the molecular level. Fatty acids are chains of hydrocarbons 4-

22 (or more) carbons a long with a carboxyl group


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at one end. If each carbon has two hydrogen atoms, the fatty ac saturated (monounsaturated). If

more than two carbon atoms are unsaturated, the fatty acid is polyunsaturated.

Question 8:

Can you describe what happens when milk is converted into curd or yoghurt, from your

understanding of proteins.

Solution 8:

Milk contains a protein called casein. This protein gives milk its characteristic white colour. It

is of high nutritional value because it contains all the essential amino acids required by man's

body. The curd forms because of the chemical reaction between lactic acid bacteria and casein. When curd is added to milk, the lactic acid bacteria present in it cause coagulation of casein and

thus, convert it into curd.

Question 9:

Can you attempt building models of biomolecules using commercially available atomic

models (Ball and stick models).

Solution 9:

Yes, we can make models of biomolecules using commercially available atomic models.

Question 10:

Attempt titrating an amino acid against a weak base and discover the number of dissociating

(ionisable) functional groups in the amino acid.

Solution 10:

When an amino acid is titrated against a weak base. It dissociates and gives two functional

groups: (i) - COOH group (carboxylic group) (ii) Amino group (NH2)


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Question 11:

Draw the structure of the amino acid and alanine. Answer

Solution 11:

Question 12:

What are gums made of? Is fevicol different?

Solution 12:

Gums are made of carbohydrates, i.e., L-rhamnose, D-galactose and D-galacturonic acid, etc.

Fevicol is different from natural gums. It is a synthetic product.

Question 13:

Find out a qualitative test for proteins, fats and oils and starch amino acids and test any fruit

juice, saliva, sweat and urine for them.

Solution 13:

(i) A qualitative test for proteins. (i) Xanthoproteic Test

Experimental Material Observation Inference

(a) Urine Yellow

precipitate

Formation of yellow precipitate

(b) Water No precipitate indicates the presence of protein in the

food material.

(ii) A qualitative test for fats. Emulsification Test


(a) Sweat Oil droplets Formation of oil droplets

(b) Water No oil droplet i.e., emulsification indicates the presence

of fats in the given food material.

(iii) A qualitative test for oils. Paper Test


(a) Food material

(sample) (b) Water

Paper

becomes

Translucent

Opaque paper becomes translucent which

indicates the presence of fats in the

food material.

(iv) A qualitative test for starch. Iodine Test


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(a) Fruit juices (b)

Water

Blue black

colour

Formation of blue black colour indicates the

presence of starch in the given food material.

Question 14:

Find out how much cellulose is made by the plants in the biosphere and compare it with how

much of paper is manufactured by man and hence, what is the consumption of plant material by

man annually. What a loss of vegetation?

Solution 14:

Most paper is formed from wood pulp. The main component of wood pulp is cellulose, a polymer

made of many glucose molecules linked together. The cellulose molecules and their bonding to

each other give paper its properties. About 33% of all plant matter is cellulose. The cellulose

content of cotton is 90% and that of wood is 40-50%. For industrial use, cellulose is mainly

obtained from wood pulp and cotton. It is mainly used to produce paperboard and paper; to a

smaller extent. It is converted into a wide variety of derivative products such as cellophane and

rayon.

Question 15:

Describe the important properties of enzymes.

Solution 15:

(i) Enzymes are proteins which catalyse biochemical reactions in the cells.

(ii) They are denatured at high temperatures.

(iii) Enzymes generally function in a narrow range of temperature and pH. Each enzyme shows

its highest activity at a particular temperature and pH called the optimum temperature and

optimum pH.

(iv) With the increase in substrate concentration, the velocity of the enzymatic reaction rises at

first. The reaction ultimately reaches a maximum velocity (v max) which is not exceeded

by any further rise in concentration of the substrate.

(v) The activity of an enzyme is also sensitive to the presence of specific chemicals that bind to

the enzyme.

(vi) Enzymes are substrate specific in their action.

Question 16:

It is said that elemental composition of living organisms and that of inanimate objects (like

earth’s crust) are similar in the sense that all the major elements are present in both. Then what

would be the difference between these two groups? Choose a correct answer from among the

following.

(a) Living organisms have more gold in them than inanimate objects

(b) Living organisms have more water in their body than inanimate objects


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(c) Living organisms have more carbon/ oxygen and hydrogen per unit mass than in animate

objects

(d) Living organisms have more calcium in them than inanimate objects

Solution 16:

(c) All living organisms and non-living matter in our biosphere are made of similar elements

and compounds. Several researches performed on plants, animals and microbes confirmed that

a relative abundance of organic compound i.e., carbon, hydrogen and oxygen in living

organisms than in the earth's crust (non-living matter). Whereas, the percent composition of

other inorganic molecules like calcium and gold is more in earth's crust as compared to living

matter. Representation of inorganic constituents of lining tissues.

Element

%Weight in

Earth’s

Crust Human Body

Hydrogen (H) 0.14 0.5

Carbon (C) 0.03 18.5

Oxygen (O) 46.6 65.0

Calcium (Ca) 3.6 1.5

Question 17:

Many elements are found in living organisms either free or in the form of compounds. One of

the following is not found in living organisms.

(a) Silicon (b) Magnesium (c) Iron (d) Sodium

Solution 17:

(a) Silicon is not found freely in nature, but it does occur as oxides and silicates, whereas

magnesium, iron and sodium are present in living organisms as ions. Silicon is essential to plant

life but is often found in minute quantities in human body and its function is still unknown.

Magnesium is an abundant element. It is essential for a number of enzymes and their action,

particularly those utilising ATP. Iron is an important constituent of. hemoglobin and plays a vital

role by taking part in 2O transport, and electron transport chain. Sodium plays a vital role in

animals by regulating nerve impulse transmission and altering the membrane permeability. It

also has indispensable role in osmoregulation.

Question 18:

Amino acids have both and amino group land a carboxyl group in their structure. Which amongst

the following is an amino acid?

(a) Formic acid (b) Glycerol (c) Glyolic acid (d) Glycine

Solution 18:

(d) Glycine is the simplest amino acid with an amino group and a carboxyl group. Whereas

formic acid is the simplest carboxylic acid, glycerol is a fatty acid and glycolic acid is carboxylic

acid substituted with hydroxyl group.


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Question 19:

An amino acid under certain conditions have both positive and negative charges simultaneously

in the same molecule. Such a form of amino acid is called

(a) Acidic form (b) basic form

(c) aromatic form (d) zwitterionic form

Solution 19:

(d) A zwitterion is a neutral molecule having both the cationic and anionic charges on the same

molecule. Amino acids are the best known examples of zwitterion. In acidic solution' amino

group accepts a hydrogen ion to become positively charged. Whereas, in alkaline solution the

carboxyl group donates a hydrogen ion to become negatively charged. The pH at which the

amino acid is electrically neutral is called isoelectric pH.

Question 20:

Which of the following sugars have the same number of carbon as present in glucose?

(a) Fructose (b) Erythrose (c) Ribulose (d) Ribose

Solution 20:

(a) Fructose is a ketohexose. Its carbon is attached to an hydrogen atom by a single bond and to

an oxygen atom by a double bond.

Erythrose is atetrose carbohydrate )OH(C 444 Its a part of tetrose family and possesses

one aldehyde group.

Ribulose is aketopentose, containing five carbon atoms and Includes ketone' as functional

group.


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Ribose is a pentose which is a major component of DNA and RNA.

Question 21:

An add soluble compound formed by phosphorylation of nucleoside is called

(a) nitrogen base (b) adenine (c)sugar phosphate (d) nucleotide

Solution 21:

(d) Each nucleoside is made up of cyclic nitrogenous base, purine or pyrimidine and apentose

sugar. On phosphorylation, it forms a nucleotide i'.e., a. molecule 'with ,-nitrogenous-

basepentose sugar and three phosphate groups,

Question 22:

When we homogenize any tissue in an acid, the acid soluble pool represents

(a) cytoplasm (b) cell membrane (c) nucleus (d) mitochondria

Solution 22:

(d) On homogenizing any tissue in an acid, the acid soluble pool represents cytoplasm.

Homogenization is a process whereby a biological sample is brought to a state such that all

fractions of the sample are equal in composition.

Question 23:

The most abundant chemical in living organisms could be


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(a) protein (b) water (c) sugar (d) nucleic acid

Solution 23:

(b) There is abundance of water in living matter. It is the only polar molecule in living organisms,

that can diffuse through a cell membrane without active transport. It is vital for a number of

metabolic reactions and one of the raw materials for photosynthesis.

Question 24:

A homopolymer has only one type of building block called monomer repeated

(a) 20 types of monomers (b) 40 types of monomers

(c) 30 types of monomers (d) only one type of monomer

Solution 24:

(a) Proteins are heteropolymers made of about 20 different kinds of monomer, i'.e., amino acids.

Each of these amino acids is made up of carbon, amino group, carboxyl group, hydrogen and a

functional group. This variable R group is what that makes each monomer different from one

another.

Question 25:

Proteins perform many physiological functions. For example, some functions as enzymes. One

of the following represents an additional function that some proteins discharge

(a) Antibiotics (b) Pigment conferring colour to skin

(c) Pigments making colours of flowers (d) Hormones

Solution 25:

(d) Proteins can sometimes function as hormones, i.e., peptide hormones such as insulin, growth

hormone etc. Other compounds such as antibiotics, florigen and melanin are non-proteineceous

in nature.

Question 26:

Glycogen is a homopolymer made of

(a) glucose units (b) galactose units (c) rigose units (d) amino acids

Solution 26:

(a) Glycogen is the storage polysaccharide present in animals. Glycogen consist of glucose

molecule linked together with α(1 4) linkages with α(1 6) branch points occurring every

8-12 residues. Galactose, on the other hand is a monosaccharide, and combines with glucose

through condensation reaction, resulting in the formation of disaccharide, lactose. Ribose is a

pentose monosaccharide which has all hydroxyl group on the same side in fisher projection. It

forms a part of backbone in RNA and DNA. Amino acids are the monomers of proteins.


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Question 27:

The number of ‘ends’ in a glycogen molecule would be

(a) Equal to the number of branches plus one

(b) Equal to the number of branch points

(c) One

(d) Two, one on the left side and another on the right side.

Solution 27:

(a) Glycogen is the multi branched polysaccharide of glucose units popularly known as animal

starch, as it is chemically similar to starch. It has 30,000 glucose residues and a molecular weight

of about 4.8 million. Glucose residues in glycogen are arranged in a highly branched bush like

chains. There are two main linkage patterns, observed in glycogen, i.e., a 1-4 linkage in the

straight part and a 1-6 linkage in the area of branching. The distance between two branching

points is 10-14 glucose residues. Glycogen has as many non-reducing ends as branches plus

Question 28:

The primary structure of a protein molecule has

(a) two ends (b) one end (c) three ends (d) no ends

Solution 28:

(a) The primary structure of a protein refers to a linear sequence of amino acids in polypeptide

chain, held together by peptide bonds. These are two ends of a polypeptide chain, carboxyl

terminus (C-terminus) and the amino terminus (N-terminus) based on the nature of the free

group on each extremity.

Question 29:

Which of the following reactions is not enzyme mediated in biological system?

(a) Dissolving CO in water (b) Unwinding the two strands of DNA

(c) Hydrolysis of sucrose (d) Formation of peptide bond

Solution 29:

• (a) 2CO gets dissolved in water, a reaction which is not always catalyzed by any

enzyme. Unwinding and winding of the two strands of DNA is catalyzed by the enzyme


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to poisomerase. Hydrolysis of sucrose is regulated by sucrose. Peptide bonds are formed

by the action of enzyme peptidyl transferase.

Question 30:

Medicines are either man made {i.e., synthetic) or obtained from living organisms like plants,

bacteria, animals, etc., and hence, the latter are called natural products. Sometimes, natural

products are chemically altered by man to reduce toxicity or side effects. Write against each of

the following whether they were initially obtained as a natural product or as a synthetic chemical.

(a) Penicillin (b) Sulphonamide (c) Vitamin-C (d) Growth hormone

Solution 30:

(a) Penicillin is a group of antibiotics derived from fungi Penicillium and was initially used as a

natural product. (b)Sulphonamide is a synthetic chemical. It is an antimicrobial agent is the basis

of several groups of drugs. (c) Vitamin-C or L-ascorbic acid or ascorbate is a natural product

and an essential nutrient for humans. It is present in citrus fruits. (d) Growth hormone (GH or

HGH) also known as somatropin or somatropin is a peptidehormone occurring naturally in the

body. It stimulates growth.

Question 31:

Select an appropriate chemical bond among ester bond glycosidic bond, peptide bond and

hydrogen bond and write against each of the following.

(a) Polysaccharide (b) Protein (c) Fat (d) Water

Solution 31:

(a) Polysaccharide is linked by glycosidic bond. Glycosidic bond is a type of covalent bond

joining simple or units carbohydrate molecules together to form a long chain polysaccharide.

(b) Protein are linked by peptide bonds. Peptide bond is a covalent chemical bond formed

between two amino acids when the carboxyl group of one reacts with the amino group of other

causing release of water molecule. Hence, called as dehydration synthesis reaction

(condensation reaction). Peptide bonds between a chain of amino acids results in the formation

of protein.

(c) Ester bonds are formed by the reaction between carboxyl group of fatty acid and hydroxyl

group of triglycerols to form fat. Water is eliminated


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during this reaction

.

(d) Hydrogen bond is electrovalent interaction between polar molecules in which hydrogen is

bound to a highly electronegative atom, such as N, 0, S, F, etc. Water is the best known example

Question 32:

Write the name of any one ammo acid, sugar, nudeotide and fatty acid.

Solution 32:

(a) Amino acid, Leucine (b) Sugar, Lactose (c) Nudeotide, Adenosine, triphosphate (d) Fatty

acid, Palmitic acid

Question 33:

Reaction given below is catalyzed by oxidoreductase between two substrats A and A?

Complete the reaction. A reduced + A’ oxidized

Solution 33:

Oxidoreductase is an enzyme that catalyses oxidation and reductions reactions. This enzyme is

associated in catalyzing the transfer of from one molecule (the reductant), also called as

electron donor, to another molecule (the oxidant), also called as electron acceptor. The complete

reaction is

Question 34:

How are prosthetic groups different from co-factors?

Solution 34:

Prosthetic groups are organic compounds that are tightly bound to the apoenzyme, (an enzyme

without cofactor) by covalent or non-covalent forces, e.g., in peroxidase and catalase, which

catalyze the breakdown of. hydrogen peroxide to water and oxygen, haemeis the prosthetic


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group and it is a part of the active site of the enzyme. Co-factor is small, heat stable and non-

protein part of conjugate enzyme. It may be inorganic or organic in nature. Co-factors when

loosely bound to a enzyme is called coenzyme and when tightly bound to apoenzyme is called

prosthetic group.

Question 35:

Glycine and alanine are different with respect to one substituent on the a-carbon. What are the

other common substituent groups?

Solution 35:

In both the amino acids the common substituent groups are COOHNH 2 and H.

Question 36:

Starch, cellulose, glycogen, chitin are polysaccharides found among the following. Choose the

one appropriate and write against each. Cotton fibre ………….Exoskeleton of cockroach

…………….. Liver ……………….. Peeled potato ……………….

Solution 36:

(a) Cotton fibre Cellulose

(b) Exoskeleton of cockroach Chitin

(c) Liver Glycogen

(d) Peeled potato

Starch Cellulose is a long chain of linked glucose molecules and is the main component of plant

cell walls. Cotton is the purest natural form of cellulose, the cellulose content of cotton fibre is

90%. Chitin is a long chain polymer that forms the hard part of the outer integument or

exoskeleton of crustaceans and insects such as cockroach. It is also the main component of the

cell walls of fungi. Glycogen is a multi branched polysaccharide of glucose acting as a form of

stored energy in the liver of animals. lt is also found in some stored fungi. Starch is a

carbohydrate consisting of along chain of glucose units joined by glycosidic bonds, This

polysaccharide is produced mostly by green plants for energy storage ,e.g., peeled potato.

Question 37:

Enzymes are proteins. Proteins are long chains of ammo adds Linked to each other by peptide

bonds. Amino acids have many functional groups in their structure. These functional groups are

many of them at least, ion sable. As they are weak acids and bases in chemical nature, this


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ionization is influenced by pH of the solution. For many enzymes, activity is influenced by

surrounding pH. This is depicted in the curve below, explain briefly.

Solution 37:

Enzymes, generally function in a narrow range of pH. Most of the enzyme shows their highest

activity at a particular pH called optimum pH, and it declines below and above this value.

Extremely high or low pH values generally results in complete loss of activity for most enzyms.

The graph above represents the maximum enzyme activity at the optimum pH.

Question 38:

Is rubber a primary metabolite or a secondary metabolite? Metabolite? Write four sentences

about rubber.

Solution 38:

Rubber (cis1, 4-polyisopyrene) is a secondary metabolite. Secondary metabolites are chemicals

produced by plants for which no role has been found yet in growth, photosynthesis, reproduction

or other primary functions.

(i) Rubber is extracted from Have abrasiliensis (rubber tree).

(ii) It is a byproduct of the lactiferous tissue of the vessels that are in the form of latex.

(iii) it is the largest of the terpenoids because it contains over 400 isoprene units.

(iv) It is elastic, water proof and a good electrical conductor.

Question 39:

Schematically represent primary, secondary and tertiary structures of a hypothetical polymer say

for example a protein.

Solution 39:

Proteins are the large-sized, hetero polymeric macromolecules having one or more polypeptides

(chains of amino acid). Primary Structure The primary structure of a protein is the linear

sequence of amino acid structural units and partially comprises its overall biomolecular

structures. The amino acids are linked together in a sequence by peptide bonds. In the primary

structure of protein initiate from an amino-terminal (N) to the carboxyl terminal (C) end, Amino

acids in a chain First amino acid


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Last amino acid represents right and of polypeplide chain Secondary Structure It is a three

dimensional form of local segments of bipolymers such as proteins. Secondary structure of

proteins is defined by hydrogen bonds between backbone amino and carboxyl groups. Mainly

secondary structure in proteins possess two forms, i.e., α helix and p-pleated sheet. α helix is a

polypeptide chain spirally coiled to form a right handed helix. This helix may becoiled regularly

at places and at some places randomly coiled. The helix is stabilised by many hydrogen bonds

which are formed between CO of one amino acid and NH group of next fourth amino acid.

β pleated sheets two or more polypeptide chains are joined together by intermolecular hydrogen

bonds to produce a sheet like structure instead of fibre as in a-helix. The polypeptide strands in

a sheet may run parallel in same direction, e.g., keratin or in opposite direction called ant parallel

(β sheet, e.g., fibroin.

Tertiary structure involves interactions that are caused by the bending and folding of a-helix or

p-sheets leading to the formation of rods, spheres of fibres. Such interactions are typically

conferred by H-bonds, ionic bonds, covalent bonds, van der Watt’s interactions and hydrophobic

interactions or disulphide linkages It gives the protein a three dimensional conformation.


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Question 40:

Nucleic acids exhibit secondary structure, justify with example.

Solution 40:

Nucleic acids are polymeric macromolecules or large biological molecules, essential for all

known forms of life. The secondary structure of a nucleic acid molecule refers to the base pairing

interactions within a single molecule or set of interacting molecules. DNA and RNA represent

two main nucleic acids, however their secondary structures differed. The secondary structure of

DNA comprises of two complementary strands of polydeoxyribonucleotide, spirally coiled on a

common axis forming a helical structure. This double helical structure of DNA is stabilized by

phosphodiester bonds (between 5' of sugar of one nucleotide and 3 of sugar of another

nucleotide), hydrogen bonds (between bases, i.e., hydrogen of one base and nitrogen of oxygen

of other base) and ionic interactions.

Question 41:

Comment on the statement “living state is a non-equilibrium steady state to be able to perform

work.

Solution 41:

Living organism are not in equilibrium because system at equilibrium cannot perform work. The

living organisms exist in a steady state characterized by concentration of each of the

biomolecules. These biomolecules are in a metabolic flux. Any chemical or physical process

moves simultaneously to equilibrium. As living organisms work continuously, they cannot

afford to reach equilibrium. Hence, the living state is in a non-equilibrium steady-state to be able

to perform work. This is achieved by energy input provided lay metabolism.

Question 42:

Formation of Enzyme substrate complex (ES) is the first step in the catalyzed reactions. Describe

the other steps till the formation of product.

Solution 42:

Each enzyme molecule has an active site for specific binding of substrate molecules .The

enzyme work by altering the activation energy of the reaction. The catalytic site of an enzyme

can be described as follows

(i) The substrate process to the active site of the enzyme, fitting into it.

(ii) Binding of the substrate induces the enzymes to alter its shape leading to formation of the

Enzyme Substrate (ES) complex.

(iii) The active site of the enzyme, now is in close proximity with the substrate and break its

chemical bonds and a new enzyme product complex is formed.

(iv) The enzyme releases the products of the reaction and the free enzyme is ready to bind to

another molecule of substrate and run through the catalytic cycle once again.


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Question 43:

What are different classes of enzymes? Explain any two with the type of reactions they catalyze.

Solution 43:

Enzymes are divided into six classes each with 4-13 sub-classes and named accordingly by a

four-digit number.

(i) Oxidoreductases/dehydrogenases These enzymes take part in oxidation and reduction or

transfer of e . S (reduced) + S' (oxidized) S (oxidized) + S' (reduced)

(ii) Transferees These enzymes transfer a functional group from one molecule to another(other

than hydrogen). The chemical group transfer does not occur in free state.

GS'SS'GS E

(iii) Hydrolases These enzymes catalyze the hydrolysis of bonds like ester, ether, peptide,

glycosidic C-C, C-halide, P-N etc. 6126

M

2111212 OH2COHOHC

(iv) Lyases These enzymes causes cleavage, removal of groups without hydrolysis and addition

of groups to double bonds or removal of groups producing double bond.

(v) Isomerases These enzymes cause rearrangement of molecular structure to effect isomeric

changes. They are of three types, i.e., isomerases, epimerases and mutases. Glucose - 6 –

phosphate Le Fructose 6 - phosphate (Aldose to ketose group or vice-versa) Glucose - 6 –

phosphate Ma Glucose-1 -phosphate (Shifting the position of side group) Glucose 5-

phosphate B Ribulose-5-phosphate (Change in position of one constituent or carbon

group)

(vi) Ligases are enzymes catalysing bonding of two chemicals with the help of energy obtained

from ATP resulting formation of bonds such: as C, O, C, S,C, N and P O

e:g.,pyruvatecarboxyluse bCACAb Pyruvric acid OHATPCO 22

Oxaloacetic +ADP + Pi.

Question 44:

Nucleic adds exhibit secondary structure. Describe through Watson-Crick model.

Solution 44:


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Nucleic acids are long chain macromolecules which are formed by end to endpolymerisation of

large number of repeated units called nucleotides. Nucleic acids show a wide range of secondary

structures. A secondary structure is the set of interactions between bases and sugar phosphate

backbone and is responsible for the shape that nucleic acid

James Watson and Francis Crick proposed a secondary structure of DNA molecules based on

the crystallographic studies.

(i) DNA or deoxyribonucleic acid is a helically twisted double-chain polydeoxyribonucleotide

macromolecule.

(ii) The two strands of DNA run anti-parallely to each other called as DNA duplex.

(iii) The spiral twisting of DNA has two types of alternate grooves, i.e., major and minor.

(iv) One turn of 360 of the spiral has about 10 nucleotides on each strand of DNA occupying a

distance of about 3.4 nm.

(v) The nucleotides within each strand are held together by the phosphodiester bonds between

the 5' carbon of one nucleotide and the 3' carbon of the adjacent nucleotide. These strong

covalent bonds holds the sugar/phosphate backbone together.

(vi) The two strands of DNA are held together by weak hydrogen boiias between the nitrogenous

bases. These hydrogen bonds are base specific. That is adenine forms 2hydrogen bonds with

thymine CA=T and cytosine forms 3 hydrogen bonds with guanine (C G).

(vii) As specific and different nitrogen bases occur on two DNA chains, they are said to be

complementary, i.e., urine lies opposite to pyrimidine. This purine-pyrimidine pairing also

contributes to the thickness of strand, i.e., 2nm, and makes the two chains complementary.


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Question 45:

What is the difference between a nucleotide and nucleoside? Give two examples of each with

their structure.

Solution 45:

Difference between a nucleotide and nucleoside is as follows

Nucleoside Nucleotide

Nucleoside is a compound formed by the

union of the nitrogenous base with a pentose

sugar It is slightly basic in nature It is a

component of nucleotide and forms with

both ribose and deoxyribose sugars. e.g.,

cytidine, uridine, adenosine, guanosine,

thymidine and inosine.

Nucleotide is compound formed by union of

nitrogen base, a pentose sugar and

phosphate. A nucleotide is acidic in nature

Nucleotide is formed through

phosphorylation ofnucleoside e.g., AMP,

GMP, CMP, UMP, dTMP (deoxythymidine

monophosphate) 0

Question 46: Describe various forms of lipid with a few examples.

Solution 46: Lipids are the esters of higher fatty acid with alcohol, such as glycerol, etc. These can be

classified as

1. Simple Lipids are esters of fatty acids with alcohol. 77 else may be

(i)Fats: These are esters of higher fatty acids with glycerol (triglycerides).

(ii) Waxes: These are esters of higher fatty acids with alcohol other than glycerol.


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2. Compound or conjugated lipids, are those compounds which contain simple lipids and

prosthetic (other additional) group. They include

(i) Glycerophospholipids, also known as phospholipids in which one of the fatty acid is replaced

by phosphoric acid which is linked to nitrogenous groups like choline, ethanolamine, serine etc,

e.g., Lecithin and cephalin, etc.

(ii)Sphingolipids, are lipids having phosphoric acid with amine alcohol 4-sphinganine or

sphingosine instead of glycerol in addition to fatty acid and choline.

(iii) Glycolipids, i.e., those which contain spinganine with a fatty acid and amonosaccharide

sugar, e.g.,cerebrosides and gangliosides.

3. Steroids are compounds with different chemical nature but similar physical properties. Their

structure is based upon a 4 ring cyclo pentenoper hydro phenanthrene ,e.g., cholesterol.

4. Prostoglandins are derivatives of arachidonic acid and contain 20 C-atoms. These are

biologically active lipids.

What are macromolecules? Give examples. Solution 1: Question 2

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