BIOMOLECULES

BIOMOLECULES
 The living organisms are made up of an array of molecules and molecular aggregates which by
themselves are not living but are performing living functions.
 These molecules found in the cells of living organisms are known as biomolecules.

 Biomolecules are the organic substances that play a major role in the structure and functions of the
living organisms.
 They help to understand the working of living system.

CHEMICAL COMPOSITION OF CELLS

 A chemical analysis of plant and animal tissues and microbial mass shows that they are made up of
similar types of about 25 elements forming numerous compounds.
 These elements may be similar to the elements present in a rock or earth’s crust. But living organisms
have abundant carbon and hydrogen than in earth’s crust. C, H, O and N, form 95% of the dry weight of
living organisms where carbon alone forms more than 50% of it.
 The biomolecules include carbohydrates, proteins, lipids, enzymes, nucleic acids, etc.

 The chemical analysis of living tissues helps one to find out their chemical composition.

 The chemical analysis is done by the following method- acid solubility test and the ash analysis. Acid
solubility test.
 The living tissues like liver or plant vegetable are ground using trichloroacetic acid to get a paste.

 It is filtered using cotton cloth to get acid soluble filtrate and acid insoluble pellet or retentate.

 The chemicals present in both the fractions were further separated and analysed.

 The acid soluble pool contained a large number of compounds with low molecular weight of about 18 –
800 daltons and they are named as biomicromolecules.
 The acid insoluble pellet contained biomolecules of more than 800 daltons and are known as
biomacromolecules.
 They are usually made up of more than 10,000 dalton molecular weights. Some of them are inorganic
molecules and occur in aqueous phase and the others are organic molecules.
 They include proteins, nucleic acids, polysaccharides and lipids. But lipids are less than 800 dalton mw
but found in acid insoluble retentate due to their non polar ends combined with fragments of plasma
membrane.
 The important biomolecules present in living tissues are carbohydrates, monosaccharides,
oligosaccharides, lipids, proteins, nucleic acids, vitamins, enzymes, hormones, and peptides.

Ash analysis: The living tissue is dried and fully burnt to get the ash. The ash contents were
+ + ++ ++ 2– 2– 3–
chemically analysed. The ash contents contained Na , K , Ca , Mg , Cl, CO3 , SO4 , PO4 , NaCl
and CaCO3.
Cellular pool: The collection of different types of biomolecules and ions present in a cell forms a
cellular pool. It contains more than 5000 chemicals. Some of them are inorganic molecules and occur in
aqueous phase and the others are organic molecules which occur in both aqueous and colloidal phase.
The inorganic molecules do not contain carbon along with hydrogen and include salts, minerals and
water. The organic molecules contain carbon with hydrogen and they include, carbohydrates, lipids,

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amino acids, proteins, nucleotides, nucleic acids, vitamins and hormones.
Average composition of cells
Component % of the total cellular mass
Water 70-90
Proteins 10-15
Carbohydrates 3
Lipids 2
Nucleic acids 5-7
Ions 1
The cellular pool is separated from extracellular fluid in animal cells. The cellular pool maintains its
composition by intake or elimination of specific molecules. It provides the raw materials for structure
and functions of the cell.

Chemical elements in human body

Elements Percentage (%)

Oxygen (O) 65%

Carbon (C) 18.5%

Hydrogen (H) 9.5%

Nitrogen (N) 3.3%

Phosphorus (P) 1.0%

Sulphur (S) 0.3%

Calcium (Ca) 1.5%

Potassium (K) 0.4%

Sodium (Na) 0.2%

Chlorine (Cl) 0.2%

Magnesium (Mg) 0.1%

The biomolecules of a cell are classified into two types based on their molecular weight and solubility.
They are biomicromolecules and biomacromolecules.

Biomicromolecules: These are small biomolecules having low molecular weight, i.e., less than
1000 daltons. They show simple structure and high solubility. They include inorganic compounds,
water, mineral salts and smaller organic compounds like sugars, amino acids, lipids and nucleotides.
These are found in soluble fraction of filtrate except lipids which occur in insoluble fraction as they are
found in cell membrane and form vesicles which are separated as acid insoluble pool.

The biomacromolecules are large and complex chemicals of molecular weight more than 10,000
daltons. They include organic compounds like proteins, nucleic acids, and polysaccharides. They are
formed by polymerization of monomers or micromolecules.

Chemical bonds There are three types of bonds formed during polymerization of monomers.
 Glycosidic bonds: -C-O-C (O-glycosidic) or C-N-C (N-glycosidic) formed in carbohydrates.

 The monosaccharides are linked between carbons of adjacent molecules by C-O-C or C-N-C.
One monosaccharide is linked to another substance by oxygen or nitrogen atom between the
two with the release of water.

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 Peptide bonds or amide bonds : These are formed between amino group (-NH2) of one
amino acid with carboxylic group (COOH ) of next amino acid the bond formed is peptide –
CO-NH- during the for-mation of dipeptide, polypeptide or oligopeptides with the loss of water.

 Phosphodiester bonds: In nucleic acids two ester bonds are formed between one phosphate
radical and two pentose sugars of adjacent nucleosides with the loss of two molecules of
water –O-HPO2-O. This helps to form polynucleotides.

METABOLITES
 A large number of organic biomolecules are synthesized and used in metabolic reactions of cells.
These compounds formed during cellular metabolism are known as metabolites.
 They are of two types namely primary metabolites and secondary metabolites.

 The primary metabolites are products formed during normal metabolism e.g., amino acids, nucleotides,
sugars, fats, peptides and steroids etc.
 The animal tissues contain only these products. In addition to primary metabolites there are secondary
metabolites which are specialised products formed during changed metabolic reactions.
 The functions of some of the secondary metabolites are uncertain.

 They are mainly formed in plants, fungi and microbial cells.

 These include alkaloids, flavonoids, rubber, essential oils, antibiotics, scents and spices. Many of these
secondary metabolites are commercially useful to mankind, e.g., rubber, drugs, spices, scents,
pigments, flavouring substances, gums and resins etc.,

Secondary metabolites
Types Examples

Pigments Carotenoids, anthocyanins

Alkaloids Morphine, codeine

Terpenoids Monoterpenes, diterpenes

Essential oils Lemon grass oil and eucalyptus oil

Toxin Abrin, ricin

Lectin Connavalin –A

Drugs Vinblastin, curcumin

Polymeric substances Rubber, gums and cellulose

Some of them are used to defend against herbivorous animals and pathogens. Some secondary
metabolites provide colours that help in pollination and seed dispersal and some metabolites act as
antibiotics to avoid competition.

CARBOHYDRATES
 Carbohydrates are organic compounds largely made up of C, H and O. In the carbohydrates the ratio of
hydrogen to oxygen is usually 2:1 as in water.
 The general formula of carbohydrates is (CnH2On). Hence they were called hydrates of carbon by early

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organic chemists. There are several exceptions to this general formula.
 The deoxyribose has C5H10O4 where H and O are not in the ratio of 2:1. Organic substances such as
formaldehyde, HCHO and acetic acid, CH3COOH have the ratio of 1:2:1 for carbon, hydrogen and
oxygen but are not carbohydrates.
 Hence the carbohydrates can be defined as ‘polyhydroxylic aldehydes or ketones, their polymers
and derivatives’ i.e., they contain many hydroxyl groups –OH and carbonyl C=O groups. In aldoses
aldehyde group is at the end and in ketoses the ketone group is at the middle.
 The carbohydrates having aldehyde groups are called aldoses and those having ketone groups are
called ketoses. The carbohydrates form nearly 80% of dry weight of plants.

Classification: The carbohydrates are classified into three types: monosaccharides, oligosaccharides
and polysaccharides.

Monosaccharides (Gr., mono = single; L., sakcharon = sugar)

 These are simple sugars. They are sweet, readily soluble in water and crystalline made up of 3-7
carbons which cannot be hydrolysed into simpler units.
 Based on the number of carbon atoms, they are classified as trioses (3C), tetroses (4C), pentoses (5C),
hexoses (6C) and heptoses (7C) each with aldoses(-CHO) and ketoses(C=O)
 The most common monosaccharides are Pentoses and Hexoses.

1. Trioses
 These are simple sugars having 3 carbon atoms (CH2O)3, C3 H6 O3.

 Examples of trioses include glyceraldehyde and dihydroxyacetone. These are intermediary metabolites
produced during respiration and photosynthesis.

Trioses

2. Tetroses
 The simple sugars with four carbon atoms are called tetroses C4H8O4, e.g., erythrose and threose.

3. Pentoses
 The simple sugars with five carbon atoms are pentoses C5H10 O5.

 The following are the examples (i) Ribose – This is present in RNA. This is also required for the
synthesis of ADP, ATP, NAD, NADP, FAD, FMN etc. (ii) Deoxyribose – This is the pentose sugar
present in the DNA (iii) Ribulose – This is the pentose sugar of green plants accepting carbon dioxide
during photosynthesis, arabinose and xylulose form secondary wall material.

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Pentoses

4. Hexoses
These are six carbon containing simple sugars and hence are called hexoses. C 6H12O6. E.g., glucose,
fructose and galactose.
(i) Glucose- blood sugar or grape sugar is the most widely distributed hexose. This is the most common
respiratory substrate used by the living cells to get energy on oxidation. The sweet index of glucose is
70. It is also involved in the synthesis of polysaccharides (starch, glycogen etc.).
(ii) Fructose is usually seen in fruits (Fruit sugar). Honey also contains fructose also known as laevulose
as it is laevorotatory. It has sweet index of 170 and is the sweetest sugar.
(iii) Galactose or brain sugar and does not occur freely but is a component of lactose, agar, glycolipids and
glycoproteins.
It is also widely distributed. It forms polysaccharides such as pectin, gums, mucilage and mannose in
cell walls.

5. Heptoses
 These are seven carbon sugars C7H14O7. E.g., sedoheptulose and glucoheptulose.


++
The monosaccharides show two important chemical properties- they reduce cupric Cu , to cuprous
+
Cu stage and hence known as reducing sugars due to free aldehyde or ketone groups. This is the
basis for Benedict’s /Fehling/s test to detect the presence of glucose in the urine. They form glycosidic
bonds C-O-C, C-N-C. The pentoses, hexoses and heptoses occur in two forms namely open chain and
ring forms. The ring forms are of two types pyranose-hexagonal with 5 carbon and one oxygen and
furanose which is pentagonal with 4 carbon and one oxygen. The carbohydrates which rotate the
polarized light to left side are known as laevorotatory or L-forms and those which rotate it to the right
are dextrorotatory or D- forms. The D forms are more common in the living system.

Oligosaccharides (Gr., oligos = few)

Oligosaccharides are composed of two to ten monosaccharides.

1. Disaccharides:
 These are composed of two monosaccharides.

 The aldehyde or ketonic group of a monosaccharide joins with an alcoholic group of another organic

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compound by a glycosidic bond by losing a molecule of water and forms a disaccharide.
 This process is called condensation and is also known as dehydration.

 A bond formed between two monosaccharides or monosaccharides and an organic compound to form
a new compound is called glycosidic bond.
 The common examples of disaccharides are sucrose, maltose and lactose.
a. Sucrose (cane sugar): It is the most abundant sugar in plants. It is composed of a molecule of glucose
and a molecule of fructose.

The aldehyde of glucose is joined to ketone of D-fructose by C1()-O-C2() linkage. Here aldose and
ketonic groups are not exposed hence it is a non reducing sugar. It is the most stable form hence it is
used for translocation of carbohydrates in plants.

b. Maltose (malt sugar): It is also a disaccharide composed of two molecules of glucose joined by
C1()-O-C4 glycosidic bonds. The glucoses are in pyranose form. The maltose is formed by the action
of amylase on starch during the germination of seeds in plants and digestion of starch food in animals.
It is a reducing sugar.

c. Lactose (milk sugar): It is a disaccharide seen only in the milk and hence called milk sugar. It is made
up of a molecule of glucose and a molecule of galactose held by C 1()-O-C4 glycosidic bond. It is a
reducing sugar.
The disaccharides are soluble in water and are sweet in taste. They show slow diffusion through the
cell membrane.

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Difference between reducing and non reducing sugars
Reducing sugar Non-reducing sugar

1. Have a free aldehyde (CHO) or a ketone (CO) group. Lack a free aldehyde (CHO) or ketone group.

2. Reduce cupric ions (Cu++) to cuprous ions (Cu+). Do not reduce cupric (Cu++) ions to cuprous ions
E.g., glucose. (Cu+).E.g., sucrose.

2. Trisaccharides
These are composed of three monosaccharide units. E.g., raffinose which is composed of glucose,
fructose and galactose. This is a non reducing sugar seen in the phloem sap of some plants.

3. Tetrasaccharides
These are composed of four monosaccharide units. E.g., stachyose. It contains glucose, fructose and
two molecules of galactose.

4. Pentasaccharides
These are made up of five monosaccharide molecules. E.g., verbascose. It contains glucose, fructose
and three molecules of galactose.

Functions of small carbohydrates:

1. Glucose is the main respiratory substrate in cells.
2. The monosaccharides and disaccharides are storage products, e.g., glucose in grapes and blood of
animals, fructose in fruits, lactose in milk, sucrose in sugarcane and sugar beet.
3. Erythrose, a tetrose, is used in the synthesis of anthocyanins, lignin and amino acids.
4. The ribose sugar is a part of RNA, AMP, ATP and deoxyribose sugar occurs in DNA.
5. Ribulose bisphosphate is a CO2 acceptor in photosynthesis.
6. Arabinose and xylulose form cell wall materials.
7. glucoronic acid is a component of cell wall and gums.
8. The amino sugar glucosamine is a monomer of chitin, hyaluronic acid and chondroitin sulphate.
9. Mannitol is a storage product of brown algae.
10. Glucose is used for synthesis of fat and amino acids.
11. Trioses, tetroses and pentoses are intermediate products of photosynthesis.
12. Small carbohydrates form polysaccharides.
13. Oligosaccharides form recognition molecules of cells.

Polysaccharides (glycans) (Gr., poly = many)

 These are macromolecules or molecules with high molecular weight made up of a large number of
monomers held together by glycosidic bonds.
 The polysaccharides made up of one type of monomers are called homopolysaccharides (e.g.,
starch, glycogen, cellulose and chitin).
 The polysaccharides composed of more than one type of monomers are called heteropolysaccharides
(e.g., pectin, agar, peptidoglycans, glucoseaminoglycans and hyaluronic acid).
 A polysaccharide made of polymer of pentose sugar is called a pentosan. If it is a polymer of hexose
then it is called a hexosan, araban of arabinose, xylan of xylose, glucosan of glucose, fructan of
fructose, galactan of galactose.

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 The polysaccharides are not sweet and usually are insoluble in water. They are noncrystalline. The
polysaccharides based on the function are of three types, storage, structural and muco
polysaccharides.
Storage polysaccharides: They are ideal reserved food materials which can be hydrolysed to form
sugars when required for respiration and biosynthesis. They are condensed and folded into compact
masses for storage. They are non diffusible, insoluble, and do not change osmotic potential, e.g.,
starch, glycogen and inulin.

Polysaccharides (a) Amylose (b) Amylopectin

1. Starch
 The starch is an end product of photosynthesis. It is stored as small grains in amyloplasts.

 The shape of starch grains may be rounded, oval, polygonal or rod like.

 They may be simple or compound grains.

 A starch grain has a central growing point called hilum around which several concentric or excentric
layers or shells of starch are deposited e.g., potato, apple, etc. The starch molecule is a polymer of
alpha D-glucose (with –1,4–glycosidic bonds).
 It is a mixture of two polysaccharides namely a central amylose and a lateral amylopectin. Amylose is
an unbranched chain made up of 200 to 1500 glucose units.
 It will be in the form of a helix more soluble and it forms 20-30 % of starch. The amylose molecule gives
blue-black colour with iodine solution.
 The amylopectin contains 2000 to 200,000 glucose units. It is a branched helical polymer (the
branching points have –1, 6–glycosidic bonds). It gives red-violet colour with iodine solution and it
forms 70-80% of starch molecule.

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2. Glycogen
 This is also a polymer of alpha glucoses. It is the storage polysaccharide and in the vertebrates it is
stored in the muscles and liver and brain. It is also stored in fungi and some bacteria.
 The glycogen is similar to amylopectin, but it is larger and more branched chain than amylopectin and
consists of upto 3000 glucose residues.
 Glycogen is insoluble in water and forms a storage polysaccharide in animals. Hence it is called animal
starch.
 The straight chain has  1-4 glycosidic links and branches have  1-6 links.

 The glycogen is stored as ellipsoidal or flattened granules lying in contact with SER. The glycogen
gives red colour with Iodine.
Inulin (Dahlia starch): It is a low molecular weight homopolymer of 25-35 residues MW 5000 daltons
stored in roots and rhizome of compositae/asteraceae, e.g., Dahlia, bulbs of garlic and onion. It is made
up of fructose units. It is soluble in water. It is not utilized in human body and hence is used for
measuring glomerular filtration rate.

3. Cellulose
 The cellulose is a homopolymer of glucose molecules in  configuration.

 It is the most abundant organic substance on this planet occurs mainly in the plants forming nearly 50%
of the carbon content of the plants.
 Cellulose is a straight chain composed of about 6000-10000 D–glucose units joined by
 1-4 glycosidic bonds.
 The cellulose chains do not occur singly but about 2000 molecules join together by hydrogen bonds
forming microfibrils.
 The microfibrils associate with each other forming larger macrofibrils.

 These are extremely strong with a high tensile strength.

 The layers of cellulose fibrils are permeable to water and solutes.

 The cellulose forms the structural component of cell wall. Cellulose is one of the important sources of
food for some animals (ruminants and insects such as termites), fungi and bacteria. Cellulose does not
show colour with iodine solution.

Cellulose fibrils

Peptidopglycan, murein, mucopolypeptide: It is a heteropolysaccharide linked to tetra peptides

present in cell walls of bacteria. It contains two amino sugars, n-acetyl glucosamine (NAG) and N-
acetylmuramic acid (NAM).

Mucoproteins or Glycoproteins: These are heteropolysaccharides where the proteins combined with
polysaccharides. They form viscous mucous secretion in the human stomach, intestine and vagina.
These are antibacterial in function.
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Lipopolysaccharides: These are heteropolysaccharides where lipids are associated with
polysaccharides. They occur in outer membrane of Gram –ve bacteria.

Hemicellulose: It is heteropolysaccharide composed of polysaccharides xylans, galactans and

arabinose.

4. Pectin
 It is a heteropolysaccharide composed of galactose, arabinose, rhamnose and galacturonic acid.

 The pectin usually becomes bound together by calcium ions.

 It forms matrix of cell wall and helps in orientation of microfibrils in the middle lamella of plant cell walls.
It joins the cells together.
 It is soluble in water and forms sol-gel interchange and commercially used as a gelling agent.

5. Chitin
 It is a heteropolysaccharide composed of n acetylglucosamine molecules (linked together by –1,
4-glycosidic bonds).
 The chitin molecules are arranged in long, parallel and straight chains.

 Chitin is similar to cellulose in structure and function. It forms exoskeleton of arthropods and cell walls
of fungi. It is the second largest organic compound on earth. It is insoluble and impervious to water.

Biological significance of carbohydrates

1. The carbohydrates are the major constituents of plants making up 60–90% of their dry mass.
2. Some polysaccharides are important storage products in plants. E.g., Starch in plants and glycogen in
animals.
3. Monosaccharides such as glucose, fructose and galactose are the respiratory substrates utilized by all
the living organisms for the release of energy by their oxidation.
4. Pentoses namely ribose and deoxyribose form the structural components of nucleic acids.
5. The ribose is also involved in the formation of ATP, NAD, NADP, FMN and FAD.
6. Trioses such as glyceraldehyde and dihydroxyacetone are involved in the operation of Calvin cycle of
photosynthesis and glycolysis of respiration.
7. Cellulose and chitin are structural polysaccharides cellulose forms cell wall of plant cells and chitin
forms cell walls of fungi and exoskeleton of arthropods. Cellulose is commercially useful product.

PROTEINS (GR., Proteios = first)

 Proteins are polypeptide. They are linear chains of amino acid linked by peptide bonds.

 Proteins could be defined as heteropolymers made up of repeating units called amino acids.

 There are 20 different amino acids which form the building blocks for the synthesis of proteins. These
different types of amino acids make possible the synthesis of a huge variety of proteins.

Properties
 There are thousands of proteins in organisms showing specificity.

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 They are made up of one or more polypeptides of amino acid residues connected by peptide bonds-
CO-NH- bonds.
 They have high molecular weight. Some proteins are soluble in water and others form colloidal solution.
They do not pass through membrane and their passage occurs by endocytosis and exocytosis.
 They are amphoteric and show reactive groups.

 They are denatured temporarily or permanently with the loss of 3 dimensional conformation.

Amino acids
 The amino acid organic compounds containing an amino group-NH2 amino group (NH2) and an acidic
group carboxyl group (COOH) attached to the same carbon, the  carbon, hence they are called alpha
amino acids.
 They are substituted methanes.

 There are four substituent groups occupying four valency positions.

 They are H, COOH, amino and a variable group named as R group.

 Based on the R group there are many amino acids. But in proteins there are only 20 amino acids. The
R group in these amino acids could be Hydrogen e.g., Glycine, and methyl group e.g., Alanine,
hydroxymethyl e.g., serine shown in the diagrams.
 The chemical and physical properties of amino acids essentially is of amino, carboxyl and the R
functional group. Based on the number of amino and carboxyl groups there are three types of amino
acids.
(1) Acidic contains two –COOH groups e.g. Glutamic acid.
(2) Basic – contains two amino groups e.g.Lysine
(3) Neutral – one –COOH and one –NH2 group e.g.valine

Hence, in solutions of different pHs, the structure of amino acid changes.

R R R
+ +
H3N CH COOH H3N CH COO H2N CH COO
(A) (B) (C)
Zwitter ion

COOH COOH
H C NH2 H C NH2
H CH3
R-side chain Glycine Alanine

COOH
H C NH2
Serine CH2 OH
Tryptophan

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 When two amino acids are linked to each other through a peptide bond they form a dipeptide. The
three amino acids condense to form a tripeptide. If many amino acids condense then it results in the
formation of a polypeptide.
 Some of the amino acids cannot be synthesized in the human body.

 They should be supplied through the diet and are called essential amino acids.

 The essential amino acids are arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine,
threonine, tryptophan and valine. (10 amino acids are essential for the growing children. Arginine and
histidine are not essential to the adults. Hence these amino acids are called semi-essential)

Non-essential Essential

Alanine Methionine

Arginine* Threonine

Asparagine Valine

Asparate Isoleucine

Cysteine Phenyl alanine

Glutamate Tryptophan

Glutamine Leucine

Glycine Lysine

Histidine*

Proline

Serine

Tyrosine

st
Note : Selenocysteine is 21 amino acid (essential)

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Functions of amino acids
1. They are building blocks of proteins, their number and sequence forming different types of proteins.
2. Glycine forms porphyrin nucleus in chlorophyll and heme protein in haemglobin and cytochromes.
3. Cysteine forms disulphide bridges among polypeptides.
4. Tyrosine in animals is converted into melanin pigment.
5. Ornithine and citrulline are involved in urea cycle.
6. Diaminopimelic acid forms bacterial cell wall of peptidoglycans.

Structure of proteins
Proteins are heteropolymers of amino acids.
They show four levels of organization namely primary, secondary, tertiary and quarternary.
(1) Primary structure: The primary structure is linear sequence of amino acid forming the backbone of
proteins. The sequence of amino acid is determined by DNA codes through transcription and
translation. This is important but does not form a functional protein. Sanger determined the primary
structure of insulin made up of 51 amino acids, 21 in  chain and 30 in  chain.

(2) Secondary structure : The polypeptide chain is coiled or folded into a spiral or helix into a three
dimensional form.
 The secondary structure is maintained by intra or inter molecular hydrogen bonds between amino acids
of same or different polypeptide chains.
 There are three types of secondary structures ,  and collagen helix. In  helix polypeptide chain is
right handedly coiled spiral. E.g., keratin of hair, myosin of muscle fibres.
 In  pleated sheet two or more polypeptide chains are joined by intermolecular hydrogen bonds forming
sheets.
 In collagen helix three polypeptides are coiled around each other and joined by H bonds, e.g., fibroin of
silk, spider web, etc.

(3) Tertiary Structure: This structure was proposed by Kendrew and Perutz (1963).
 It is a folding and coiling of secondary structure to form a compact structure with functional sites. It is a
3- dimensional arrangement of protein structure.
 This gives stability to a protein. There are H and disulphide bonds –S-S- ionic and hydrophobic
interactions.
 The non polar groups of amino acids are covered and polar groups are exposed.

 The biological functions of proteins depend on the tertiary structure.

 The functional 3-D structure is called native state. It is changed by pH, changes in temperature which
also change the functions of proteins.

(4) Quarternary structure: This structure is formed by two or more polypeptides called oligomers.
 Each polypeptide has primary, secondary and tertiary structure. E.g., insulin with two polypeptide
chains, haemoglobin with four polypeptide chains have quarternary structures.
 The monomeric units are held by non covalent bonds like hydrogen, hydrophobic and ionic bonds.

 The three dimensional structure of haemoglobin was elucidated by Kendrew and Perutz (1963).

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Various Levels of Protein Structure

Cartoon Showing : (a) A secondary Structure and (b) A tertiary structure of proteins

Types of proteins
Proteins are classified on the basis of shape and chemical composition and function.
Based on shape there are two types of proteins-fibrous and globular.
Fibrous proteins: These are proteins with spiral secondary polypeptide chains wound to form fibres.
They are insoluble non enzymatic and structural proteins. E.g., collagen and elastin of connective
tissue, keratin of hair, fibroin of silk fibrin etc.
Globular proteins: These are spherical, soluble proteins which are non-contractile, showing tertiary or
quarternary structure. These form enzymatic or non enzymatic proteins, e.g., egg albumins, serum
albumin and glutelins, (e.g., wheat and maize).

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Biological significance of proteins
Proteins are of great importance to the living organisms as they play a central role in determining their
structure and functions.
1. Structural proteins: Several proteins serve as building material of cells and are called structural
proteins. They play a major role in growth and repair. They determine the structure of cell membranes,
ribosomes, mitochondria, plastids, microfilaments, microtubules, flagella and cilia etc., Some of the
proteins form extra cellular supporting structures such as collagen and elastin of connective tissues,
 keratin in skin, feathers, hair, horn etc., These structures form protective coverings. The cocoon of
silk moth is composed of silk fibres of white and insoluble protein called fibroin.
2. Functional proteins: Proteins are work horses of the cells. They perform a variety of functions.

3. Enzymes: These are biocatalysts regulating the metabolism. E.g., Ribulose bisphosphate carboxylase
oxygenase (RuBisCO), glutamine synthetase, amylase etc.
4. Hormones: Several hormones are proteinaceous. E.g., insulin and glucagon for regulation of glucose
metabolism and growth hormone for the growth of the body. Hormones are chemical messengers for
coordinating the functions of the body.
5. Transport proteins: The proteins also function as carriers or transporters. E.g., Haemoglobin
transports oxygen in the blood of vertebrates, haemocyanin transports oxygen in the blood of some
annelids, molluscans and arthropods. Serum albumin transports lipids in the blood of vertebrates.
6. Protective proteins: Some of the proteins protect the body in various ways. E.g., antibodies defend
the body against the invasion by the microbes or foreign substances. Fibrinogen of the blood forms the
clot at the site of injury of the blood vessel and protects the body from the loss of the blood.
7. Contractile proteins: The contractile proteins such as myosin and actin present in the muscles of
animals bring about the movements.
8. Storage proteins: The storage proteins are usually globular proteins (spherical in shape). E.g., egg
albumin, serum albumin, serum globulins, casein (milk protein) and aleurone protein in seeds
(prolamines and glutelins in wheat).
9. As buffers: Proteins also help in maintenance of pH and regulation of volume of body fluids.
10. Receptor proteins: a number of proteins of plasma membrane act as receptor molecules to bind with
hormones.
11. Some proteins act as biological buffers and form visual pigments like iodopsin and rhodopsin.
12. Some proteins act as repressor proteins to regulate gene action.
13. Some act as toxins e.g., bacterial toxins and ricin.

LIPIDS (gR., LIPOS = FAT)

 These are micro molecules, non polar and insoluble in water but soluble in non polar organic solvents
like ether, chloroform, acetone etc.
 They do not polymerise and form macromolecules but combine with carbohydrates and proteins to form
large molecules.
 Lipids are usually defined as organic compounds insoluble in water but soluble in organic solvents such
as ether, ethyl alcohol, benzene etc.,

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 The true lipids are esters of fatty acids and an alcohol (such as glycerol).

 The lipids contain C, H and O. The number of oxygen atoms is very less in lipids.

 The lipids are diverse group of organic compounds.

 They can be classified into simple, compound and derived lipids.

 The lipids are made up of fatty acids and glycerol.

Fatty acid: It is an unbranched chain of hydrocarbons ending with a carboxylic group-COOH.
 The fatty acid has a carboxyl group attached to an ‘R ‘group.

 The ‘R’ group could be a methyl –CH3 or ethyl –C2H5 or higher number of –CH2 groups (one to 19
carbons) For e.g., palmitic acid has 16 atoms including carboxyl carbon.
 Arachidonic acid has 20 carbon atoms including carboxyl carbon.

 The carbon hydrogen bonds are non polar hence fatty acids are insoluble in water, but –COOH group
gives acidic properties and contains polar group C=O and –OH groups. Hence it is soluble in water.
 A fatty acid cannot dissociate in fat molecule hence it is known as neutral fat. The insolubility is due to
repulsion present between non polar groups.

Lipids
 Most of the fatty acids have an even number of carbon atoms, 14-22 (mostly 16-18).

 The plants and majority of animals synthesize all fatty acids some animals and humans cannot
synthesize some fatty acids, e.g., linoleic acid, linolenic and arachidonic acids.
 They are known as essential fatty acids.

 They have to be got from diet. Essential fatty acids occur in most edible oils like those of sunflower,
groundnut, cotton seed, coconut, etc.

Glycerol

Fatty acids are of two types: saturated and unsaturated.

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(1) Saturated fatty acids
 The fatty acids which contain only single bonds in their hydrocarbon chains are saturated fatty acids.
 They do not have double bonds.

 They have higher melting point and hence solids at room temperature with general formula C nH2nO2,
e.g., butyric acid, capric acid, caprilic acid in onion bulbs, stearic, palmitic and arachidic acids.

(2) Unsaturated fatty acids

 These are fatty acids with double bonds.

 They have one or more double bonds in their hydrocarbon chain.

 They have low melting point and are liquids at room temperature.C nH2n-2xO2 (where x is the number of
double bonds) based on the number of double bonds they are named as monoenoic - with one double
bond, dienoic with two double bond and trienoic - with three double bonds, e.g., oleic acid, linoleic acid,
linolenic and arachidonic acid.
 Fatty acids with more than one double bonds are called polyunsaturated fatty acids (PUFA). They do
not form atherosclerosis, e.g., sunflower oil, safflower oil etc. The double bonds form bends of
hydrocarbon chains. Hence they are liquids at room temperature.

Differences between saturated and unsaturated fatty acids

Saturated fatty acids Unsaturated fatty acids

1. Only single bonds between carbon Contain one or more double bonds between carbon
bonds. bonds.

2. Solids at room temperature. Liquid at room temperature.

3. Higher melting point. Lower melting point.

4. Found mostly in animals Found in plants.

Examples: Butyric acid, lauric acid, Examples: Oleic acid, linoleic acid
stearic acid.

Both plants and animals possess biosynthetic machinery for the synthesis of fatty acids. But many
animals lack the mechanism to synthesise three fatty acids- linoleic, linolenic and arachidonic acids.
These are called essential fatty acids.
Glycerol: It is an alcohol with a backbone of three carbons, each carrying an OH group.

R1

R2

R3

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Fat
When its three OH groups react with COOH groups of fatty acids a triple ester or triglyceride or
triacylglycerol is produced with the release of three molecules of water.

Classification of lipids
Lipids are classified into three types: simple, compound and derived.

(1) Simple lipids

These are formed of fatty acids and alcohol, e.g., fats, suberin, cutin and wax.

 Neutral Fats:
 These are esters of fatty acids and glycerol. They occur abundantly in nature as reserve food materials.

 During their condensation one glycerol reacts with three fatty acids with the release of 3H 2O molecules.
The triglycerides are common fats.
 The pure fats have three similar fatty acids.

 Fats with dissimilar fatty acids are known as mixed fats.

 Most of the fats are mixed fats.

 The fats are of two types, namely oils and fats.

Oils:
 These are liquids at room temperature and are rich in unsaturated fatty acids.

 They have short chain fatty acids and have low melting points. E.g., groundnut oil, rape seed oil,
mustard oil, sesame seed oil, safflower oil and sunflower oil etc.
 Vegetable oils are having more than one double bonds hence known as polyunsaturated fatty acids
(PUFA).
 They are good fats as they lower blood cholesterol.

 The oils are converted into fats by hydrogenation to form saturated hard fats.
Hard fats :
 These are solids at room temperature and they contain long chains of saturated fatty acids and show
high melting points, e.g., animal fat butter is soft due to short chain fatty acids.
 They act as insulators checking the loss of heat from the body of animals.

 They also act as padding materials of the animals protecting the internal organs and also organs which
are exposed to mechanical pressure.

Neutral fat
 The fats could be pure or mixed. If they have three fatty acids of the same type then they are called
pure fats.
 Most of the fats are mixed and have dissimilar fatty acids, e.g., Dipalmitostearin, palmito oleic stearin,
etc.,).
 Butter fat is the oily component of milk. It is a mixed fat composed of oleic acid, stearic acid and palmitic
acid attached to glycerol.
 It is a source of energy for the developing young ones of mammals.

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Waxes:
 These are long chain fatty acids esterified to a long chain alcohol. E.g. Bee wax is composed of palmitic
acid and mericyl alcohol.
 It is secreted by abdominal glands of worker bees. It is thick and is used for building hive.

 The plant waxes form a water proofing coat on the epidermis to reduce transpiration in land plants and
prevent wetting in aquatic plants.
Lanolin or wool fat:
 It is a secretion of cutaneous glands of sheep which forms water proof coating on animal hair and skin.
Sebum:
 It is secreted by sebaceous glands of human skin.
Cerumen:
 It is ear wax secreted by external auditory canal which lubricates ear drum.
Paraffin wax:
 It is obtained from petroleum and used in cosmetics and polishes.

(2) Compound lipids

 These lipids not only have the esters of fatty acids and alcohol but also have other substances.

Phospholipids:
 These are tri glycerides with one fatty acid replaced by phosphate attached to a nitrogenous base.

 The phospholipids are amphipathic, which contain both hydrophilic polar and hydrophobic non polar
groups.
 The phosphate group and nitrogenous base together form polar head and the hydrocarbon forms
nonpolar tail.
 The phospholipids form the components of cell membranes.

 In aqueous medium the phospholipids form a bilayer with non polar hydrophobic tails towards the
centre and hydrophilic heads facing outwards.
 The phospholipids are further classified on the basis of organic base that they contain

Lecithins
 Lecithin usually contains glycerol, two fatty acids, phosphoric acid and an organic base called choline.

 Hence lecithin is called phosphatidyl choline.

 The choline is attached to phosphoric acid.

 The fatty acids present in lecithins may be unsaturated or saturated.

 It is abundantly present in various tissues (heart, lungs, liver and brain).

 It is also present in the plasma. In the lungs dipalmityl lecithin forms surfactant which prevents collapse
of alveoli.
 It helps in reducing the pressure required for expansion of alveoli during breathing.

 Lecithins also help in the emulsification of fats.

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Cerebroside:
 Cerebroside is a type of glycosphingolipid where galactose is the carbohydrate group.

 The cerebrosides are seen in the human serum, spleen, liver and brain. They are present in large
amounts in the white matter of brain and in the myelin sheath of nerves.
Lipoproteins:
 These are lipids associated with proteins, occur in blood, milk and egg yolk.
Cutin:
 It occurs in plant cell walls and cuticle to reduce transpiration.

 Suberin occurs in cells walls of cork cells and is impermeable to water.

(3) Derived lipids

Sterols and steroids:
 Steroids are lipid like compounds containing a tetracyclic nucleus, namely
cyclopentanoperhydrophenanthrene (CPPP) ring. It consists of a penanthrene nucleus-A, B, C-3
hexanes and a cyclopentane D’ pentose ring joined to a long hydrocarbon chain, e.g., Cholesterol,
ergasterol, stigmasterol, bile salts, sex hormones, adrenocorticosteroids, cardiac glycosides etc., A
steroid with hydroxyl group is sterol.
Cholesterol:
 It is found in animals and is synthesized in liver, adrenal cortex, skin and intestine, kidney.

 It is a component of cell membrane and is insoluble in water.

 The cholesterol forms gall stones in gall bladder.

 It is the raw material for the synthesis of steroid hormones like sex hormones-progesterone, estradiol,
testosterone and cortisone etc.
 It forms bile salts which help in emulsification of fats during digestion.

 It forms components of cell membranes of animal cells and mycoplasma.

 The cholesterol forms vitamin-D in skin upon exposure to sunlight.

 The excess of cholesterol forms low density lipoproteins (LDL) and very low density lipoproteins and
(VLDL). They cause atherosclerosis in blood vessels.

Biological significance of lipids

1. Lipids are present as insulation layer in the skin of animals. This layer is very thick in the mammals
adapted to the cold climatic conditions, e.g., whales, porpoises and dolphins (called blubber). The
migratory birds store the food mainly in the form of lipids because one gram of fat on oxidation gives
more amount of energy than a gram of either carbohydrates or proteins. The oxidation of fat also
releases more amount of metabolic water than the other organic substances. Seeds and fruits of plants
are usually rich in oils, e.g., coconut, sunflower, groundnut, castor, soya bean, etc. These are utilized as
a source of energy during germination.
2. Waxes act as water proofing substances, e.g., in plants cutin and suberin and in animals wax is present
in the skin, fur and feathers.
3. Phospholipids such as lecithins and cephalins are present in the cell membranes.
4. Glycolipids such as cerebrosides form the myelin sheath of nerve cells. Glycolipids are also seen in the
membrane of chloroplasts.

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NUCLEIC ACIDS
 Friedrich Meischer (1868) discovered the nucleic acids (DNA) in the nuclei of the pus cells and named
them as nuclein.
 The nucleic acids are macromolecules forming the hereditary determinants of the living
organisms.
 Even though the name nucleic acids suggest their location in the nucleus but they are also seen in the
organelles such as mitochondria, chloroplast and in the cytoplasm.
 Altmann (1899) gave the name nucleic acid. They are made up of a large number of nucleotides hence
known as heteropolymers of nucleotides.

Nucleotides
 The nucloetides are monomers of nucleic acids.

 They are small but complex molecules.

 The nucleotides are made up of three moieties, a pentose sugar, a cyclic nitorogenous base and a
phosphoric acid.
 Thus nucleotides are composed of C, H, O and N.

Pentose sugars:
 It may be ribose sugar C5H10O5 or deoxy ribose sugar, C5 H10 O4. These sugars occurs as pentagon or
furanose form with four carbons and one O2 forming a ring.
 The fifth carbon is outside the ring forming CH2OH. At carbon 2 position OH is replaced by hydrogen
in deoxyribose.
 The deoxyribose is found only in DNA. The ribose sugar occurs in RNA and free cytoplasmic
nucleotides – ATP, AMP, NAD and FAD and inside coenzyme A.

Nitrogenous bases:
 These are heterocyclic compounds of two types- purines and pyrimidines.

 The pyrimidines are six carbon single rings having nitrogen at one and three positions.

 There are three types of pyrimidines, namely, cytosine (C), thymine (T) and uracil (U).

 The purines are nine carbon double ring nitrogenous bases with nitrogen at 1, 3, 7 and 9 positions.
There are two types of purines, namely, Adenine (A) and Guanine (G).

Phosphoric acid H3PO4:

 It is known as phosphoric acids (P).

 The three OH and one O2 attached to one, two or three phosphate groups.

 A combination of nitrogenous base and pentose sugar joined at 1'C position by glycosidic bond by one
of its nitrogen atoms usually N3 in pyrimidine and N9 in purine to form a nucleoside.
 There are four nucleosides with ribose and deoxyroibose sugars.

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Nucleosides of RNA and DNA

Ribonucleic acid (RNA) Deoxyribo nucleic acid (DNA)

1. Adenine + Ribose sugar = adenine nucleoside Adenine + Deoxyribose sugar = dadenine

(adenosine) nucleoside

2. Guanine + Ribose sugar = guanine nucleoside Guanine + Deoxyribose sugar = dguanine

(guanosine) nucleoside

3. Uracil + Ribose sugar = uracil nucleoside Thymine + Deoxyribose sugar = dthymine

(uridine) nucleoside

4. Cytosine + Ribose sugar = cytosine nucleoside Cytosine + Deoxyribose sugar = dcytosine

(cytidine) nucleoside

Nucleotides:
 These are formed by condensation of pentose sugar, a nitrogenous base and a phosphoric acid
residue.
 The sugar is bound to nitrogenous base at 1'C and PO 4 at 5'C.

 The nitrogenous base is connected to pentose sugar at N1 of pyrimidine-C, T, U and N9 of purine A/G.

 There are four ribonucleotides and four deoxyribonucleotides .

Nucleotides of RNA and DNA
Ribonucleotide Composition Symbol Deoxyribonucleotide Composition Symbol

1. Adenosine Ribose + AMP Deoxyadenosine Deoxyribose + Adenine dAMP

Monophospate Adenine + monophospate + Phosphate
(Adenylic Acid). Phosphate (deoxyadenylic acid)

2. Guanosine Ribose + GMP Deoxyguanosine Deoxyribose + Guanine dGMP

Monophospate Guanine + monophospate + Phosphate
(Guanylic Phosphate (deoxyguanylic acid).
Acid).

3. Cytidine Ribose + CMP Deoxycytidine Deoxyribose + Cytosine dCMP

Monophospate Cytosine + monophospate + Phosphate
(Cytidylic Acid). Phosphate (deoxycytidylic acid).

4. Uridine Ribose + UMP Deoxythymidine Deoxyribose + Thymine dTMP

Monophospate Uracil + monophospate + Phosphate
(Uridylic Acid). Phosphate (deoxythymidylic
acid).

 The ribonucleotides are monomers of RNA and also occur freely in cells. They also form higher
nucleotides.
 The deoxyribonucleotides are basic units of DNA.

 Uridine monophosphate or uridylic acid occurs only in RNA and thymidylic acid or thymidine
monophosphate occurs only in DNA.
 The cyclic AMP or adenosine 3, 5 monophosphate or cAMP is derived from ATP in presence of
adenylate cyclase.
 It acts as a second messenger of the cells.

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Formation of nucleic acids
 The nucleic acids are macromolecules of living organisms.

 They are heteropolymers of purines and pyrimidine nucleotides.

 The nucleic acids are formed by polymerization of a large number of nucleotides.

 The adjacent nucleotides are joined by phosphodiester bonds between phosphate and 5'C and 3'C of
pentose sugar.
 The PO4 is linked to 5'C and 3'C of pentose sugars of successive nucleotides.

 There are two types of nucleic acids, namely DNA and RNA.

Components of nucleic acids

Phosphate Pentose sugar Purine Pyrimidine

Deoxyribose Adenine Cytosine

Guanine Thymine
Ribose

Uracil

DNA – Deoxyribo nucleic acid

Structure:
 The structure of DNA is elucidated by Watson and Crick based on the X-Ray diffraction studies of
Wilkins and Rosalind and they proposed a double helix model.
 According to this model DNA consists of two polynucleotide strands, helically coiled around a common
axis in a right handed helix.
 These polynucleotides are formed by four types of deoxyribonucleotides adenine nucleotide, guanine
nucleotide, cytosine nucleotide and thymine nucleotide.
 The vertical bars of DNA are made up of alternate deoxyribose sugars and PO 4 groups.

 The PO4 group is attached to 5'C of sugar residue of its nucleotide and 3'C of sugar of next nucleotide
by phosphodiester bonds.
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 In the polynucleotide strand one end has 3'C is free and at other end 5'C is free.

 This polarity is known as 3'5'C ends.

 The nitrogenous bases are attached to 1'C of sugar by glycosidic bonds arranged at right angles to long
axis of DNA.
 A pyrimidine is attached to deoxyribose by its N-atom at 3'C position.

 The purine is joined by N atoms at carbon 9 position.

 The two strands of DNA are antiparallel i.e., one strand runs in 5'  3'C direction and the other in
3'←5'C.
 The two strands are held together by H bonds formed between two N2 bases.

 The purines of one strand always pair with pyrimidines of the opposite strand.

 The purine- pyrimidine pairing is also specific.

 A pairs with T by two H bonds and G pairs with C by three H bonds.

 This was explained by E.E. Chargaff and hence known as Chargaff' s rule.

Chargaff's rules include the following.

1. In DNA molecule AT base pairs are equal to GC base pairs.
2. The amount of purines and pyrimidines are equal A + G = T + C.
3. The amount of A= T and amount of G = C.
4. The base ratio of A+T/G + C is always constant for a given species. It is lower for primitive organisms
and higher for advanced organisms.
5. The deoxyribose and PO4 are in equal proportions.

 The DNA has a uniform thickness of 20Å.

 One turn of DNA measures 3.4 nm and consists of 10 nucleotides pairs.

 Thus the gap between two adjacent nucleotides is 0.34 nm. It has two types of grooves – a major or
deep groove of 2.2 nm and a minor or shallow groove of 1.2 nm.
 The specificity of pairing gives rise to infinite variety of DNA molecules.

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A polynucleotide chain

 The DNA molecule is denatured or melted at high temperature and by acid or alkali.

 This occurs due to breakdown of hydrogen bonds. When denatured DNA is incubated at low
temperature it reassociates and the process is known as reannealing.
 A = T area is known as low melting area due to two hydrogen bonds and G  C area with three
hydrogen bonds is more stable and hence known as high melting area.

(a) Duplex of DNA (b) chemical structure

RNA – Ribonucleic acid

 The ribonucleic acid is a polymer of single chain of ribonucleotides.

 It occurs in the cytoplasm of prokaryotic cells.

 In eukaryotic cells bulk of RNA occurs in the cytoplasm and small amount in the nucleus.

 The ribonucleotides of RNA consists of a ribose sugar, nitrogenous base and a phosphate. The
RNA has two purine bases and two pyrimidine bases.
 The usual purine bases are adenine and guanine.

 The usual pyrimidine bases are cytosine and uracil.

 The normal nucleotides of the RNA are adenosine monophosphate, guanosine monophosphate,
cytidine monophosphate and uridine monophosphate.
 In an RNA chain PO4 group at 5'C position of sugar in one ribonucleotide is joined to 3'C position of
sugar in the next ribonucleotide by phosphodiester bonds as in DNA.
 The nitrogenous bases are attached to 1'C position of ribose sugar by glycosidic bond and project on
one side.
 The purines and pyrimidines do not occur in equal amounts in RNA hence Chargaff’s base
complementarity rule is not applicable (dsRNAs of some viruses are exceptions, e.g., reo virus and
wound tumour virus).
 There are two types of RNAs, namely, the genetic RNA and the non-genetic RNA (Table 9.9). The
genetic RNA is responsible for the inheritance of hereditary characters.

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 The genetic RNA is found only in some viruses like TMV, polio virus, reo virus, retro virus, etc. In these
viruses the DNA is absent.
 The non-genetic RNA is involved in protein synthesis. It is synthesized by the DNA.

 There are three types of non-genetic RNAs namely, mRNA, tRNA and rRNA.

LIVING STATE, DYNAMIC STATE AND CONCEPT OF METABOLISM

 The living organisms from bacteria through protozoa, plant or animal cells, contain thousands of organic
compounds called biomolecules, in definite concentrations, expressed as moles/cell or moles/litre.
These biomolecules are constantly changed either by breaking down or synthesis into other
compounds.
 This is known as turnover. The sum total of all chemical reactions occurring in living cells is known as
metabolism.
 These metabolic reactions are enzyme catalysed reactions, e.g., removal of CO2 from amino acid forms
amine, hydrolysis of glycosidic bond in a disaccharide forms monosaccharides.
 The metabolic reactions do not occur in isolation.

 They are linked to each other to form metabolic pathways.

 The flow of metabolites through metabolic pathways shows definite rate and direction and hence known
as dynamic state of the body constituents.
 The biochemical pathways occur in separate compartments like cell organelles and are well regulated
through enzymes.
 The end products of one reaction are the substrate to next reaction and final end products are
consumed quickly or feedback inhibition stops the reaction.
 There are two types of metabolism namely, anabolism and catabolism.

Anabolism or biosynthetic pathway:

 A process where complex molecules are synthesized by smaller compounds using energy is
anabolism.
 It consumes energy hence known as endergonic reaction. e.g., nucleotides converted into nucleic
acids and amino acid into proteins.

Catabolism:
 A process wherein complex chemical compounds are degraded into simpler compounds is called
catabolism.
 These reactions are accompanied by release of energy hence known as exergonic reactions, e.g.,
glucose is degraded to lactic acid in the skeletal muscles in ten metabolic steps.
 The energy released during catabolic reactions are stored in chemical bonds called ATP.

 The ATP is called universal energy currency of the cell. ATP is formed from a purine adenine, ribose
sugar and three phosphate radicals.
 The second and the third phosphates contain high energy bonds which are represented by squiggle
bonds (PP).
 The ATP is readily formed from ADP by storing 7.34 kcal of energy and ATP gets converted into ADP
by releasing 7.34 kcal of energy.
 Hence it is known as universal energy carrier.

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 BIOMOLECULES

 In a living organism thousands of chemical compounds are present and these are known as
metabolites.
 They occur in concentrations characteristic each of them, e.g., glucose concentration in the blood of
normal individual is 4.5-5.0 mM (90-120 mg for 100 ml of blood) while the concentration of hormones in
nanograms per mL. The living system shows steady state for each of these thousands of molecules
and hence metabolites are in a state of flux called metabolic flux.
 Any chemical or physical process moves spontaneously to equilibrium at which state systems perform
work.
 Hence metabolic flux keeps the living system in a non equilibrium steady state to enable it to perform
work.
 This is done by energy input derived from metabolism. Hence, metabolism and living state are
synonymous, without metabolism living state cannot exist.

ENZYMES
Definition
 Enzymes are biological catalysts regulating chemical reactions of living organisms.

 Generally the enzymes are proteins.

 They promote a very large number of chemical reactions which occur in the living cells at the
temperatures suitable for the existence of life.
 These enzymatic reactions can occur in an orderly and regulated manner and it is indispensable for the
survival of living organisms.
High rate of enzyme controlled reactions:
 The enzymes are biochemical catalysts made up of amino acids.

 The amino acids of a tertiary structure of a protein fold and form small pockets or crevices called active
sites.
 The substrate is a metabolite upon which an enzyme acts.

 Hence enzymes are proteins with three dimensional structure with an active site which converts a
substrate (S) into a product i.e. S  P.
 The substrate ‘S’ has to bind to active site to form a enzyme substrate complex (ES), (E = enzyme, S =
substrate).
 This is a temporary state formed by substrate and active site of enzyme known as transition state in
which state bond is either made or broken quickly and product is released from the active site hence
substrate is changed to product.
 Most of the chemical reactions donot start automatically because the reactant molecules have an
energy barrier to become reactive.
 To start a chemical reaction an external supply of energy is needed.

 This energy is called activation energy.

 It increases the kinetic energy of the system and brings about collision between reactants.

 The activation energy requirement is very high.

 Example: 32000 cal/mol to hydrolyse a molecule of sucrose into glucose and fructose.

 An enzyme lowers the activation energy.

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BIOMOLECULES

 It is 9000 cal/mol for hydrolyses of sucrose.

 The energy status in an enzyme catalysed reaction is shown in the figure.

 Here ‘Y’ axis represents the potential energy content and the ‘X ‘axis represents progression of reaction
through transition state ‘T’. The ‘S’ represents energy status of reactant and ‘P’ energy status of the
product.
 There is energy level differences between ‘S’ and ‘P’. The ‘P’ is at lower energy level than ‘S’ and
product is said to be more stable.
 In a chemical reaction substrate ‘S’ has to go through a much higher energy state called transition
state.
 The difference in average energy content between ‘S’ from that of the transition state’ ‘T’ is called
activation energy.
 It is the energy required to bring about a chemical reaction. Due to high free energy of activation the
uncatalysed reactions occur slowly.

Effect of enzyme on reaction rate

 The reaction requires sufficient energy to overcome this transition state.

 By increasing temperature energized substances are increased and rate of reaction is also increased.

 An enzyme lowers the free energy of activation by binding with more intermediates and reduces their
activation energy to level T 1 and increases the rate of chemical reaction for example, hydrolysis of
sucrose in presence of sucrase or invertase requires an activation energy 9000 cal/mol but an
uncatalysed reaction requires of 32,000 cal/mol.

Properties of enzymes
1. They enhance the rate of a chemical reaction without themselves being changed or used.
2. Enzymes are very efficient in very small amounts. They convert a large amount of reactants to their
6
products. For example, a mole of carbonic anhydrase enzyme can convert 36 × 10 molecules of
carbon dioxide to carbonic acid per minute, catalase converts 5 million hydrogen peroxide into water
and oxygen per minute.
3. Enzymes are highly specific. Each of them catalyses only a specific reaction, e.g., maltase acts only on
maltose.
4. Enzymes can be denatured by heat- thermolabile human enzymes are active at 35-40° C, denatured at
50-55°C. The enzymes of bacteria living in hot springs have optimal temperature of 70°C.

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5. The activity of the enzymes is affected by pH, maximum activity shown between pH 6.5 to 7.6; but
pepsin acts at pH 1.5 to 2 temperature, pressure, substrate concentration and enzyme concentration.
6. Enzymes do not alter the type of end product produced or the nature of the reaction. The enzyme
catalysed reactions are reversible.
7. Enzymes are globular proteins with high molecular weight; some with non-protein cofactors.
8. Some enzymes are conjugated proteins known as holoenzymes. A holoenzyme contains a protein part
known as apoenzyme and a non protein part known as cofactor required for activation. The non protein
2+ 2+
part may be metal ions like Zn and Fe (Table). If apoenzymes are organic molecules they are known
+
as coenzymes which are derivatives of vitamins - NAD , FAD, riboflavin and CoA. If coenzyme is firmly
attached it is known as prosthetic group, e.g., biotin bound to carboxylase
9. Recently non protein enzymes - ribozyme – a 23s rRNA enzyme, RNAP and peptidyl transferese have
been identified by Cech, Altmann and Nollet et al., (1992).

Some inorganic elements which act as cofactors for enzymes

Inorganic Elements Enzyme Catalysed
2+
Cu Cytochrome oxidase.
2+ 3+
Fe or Fe Cytochrome oxidase, latase and peroxidase.
+
K Pyruvate kinase.
2+
Mg Hexokinase, glucose 6 - phosphatase and pyruvate kinase.
2+
Mn Arginase.
Mo Dinitrogenase.
2+
Ni Urease.
2+
Zn Carbonic anhydrase, alcohol dehydrogenase and carboxypeptidase A and B.

Enzyme classification
Naming of the enzymes in a systematic way has been introduced by the International Union of
Biochemistry (IUB) in 1961. The naming is based on the type of reaction that the enzyme catalyses.
On this basis (function) there are six groups of enzymes. They are the following.
Oxidoreductases
These transfer oxygen, hydrogen or electrons from one molecule to the other. E.g., alcohol
dehydrogenase adds H atoms to acetaldehyde.
S reduced + S' oxidized S - Oxidised + S' reduced
X Y
C C  X  Y  C  C
Alcohol dehydrogenase
CH3CHO  NADH   CH3CH 2OH  NAD
(Acetaldehyde) (Ethylalcohol)
e.g. dehydrogenases, nitrate reductase, cytochrome oxidase etc.
Transferases
These transfer a specific group from one molecule to the other than H'. E.g. transaminases.
S – G + S' S + S – G
Gulatamate pyruvate amino transferase
  ketoglutarate + Alanine
Glutamate + Pyruvate 

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Hydrolases
These catalyse the formation of two products from a substrate molecule by splitting or cleaving through
the addition of water. E.g., carbohydrases, proteases and lipases. They catalyse the hydrolysis of ester,
ether, peptide and glycocidic bonds, C – C – C, halide or P – N bonds
Fat + water 
Lipase
 Glycerol + Fatty acids
Lyases
These enzymes catalyse non hydrolytic addition or removal of chemical groups from the substrates.
E.g., decarboxylases and aldolases.
CH3COCOOH 
pyruvate decarboxylase
 CH3CHO CO2
pyruvate acetaldehyde

Isomerases
These bring about intra molecular rearrangement producing a different form of the same substance.
Dihydroxyacetone phosphate  Phosphoglyceraldehyde
Glu cose  6  phosphate 
phosphohexo isomerase
 Fructose 6  Phosphate
Ligases
These join two molecules together using energy from the ATP. (They synthesize new bonds between C
and C, C and N, C and O or C and S) P – O bonds.
Amino acid + tRNA + ATP 
Aminoacylsynthetase
Amino acyl tRNA + ADP + Pi

Mechanism of enzyme action or mode of enzyme action

The mechanism of enzyme action is explained by two theories namely- Lock and key theory and
Induced fit theory.

1. Lock and key theory:

 This was proposed by Emil Fischer 1894. According to this theory an enzyme has an active site whose
shape is complementary to the shape of the substrate molecule like lock and a key.
 The active site holds the substrate to form an enzyme substrate complex or ES complex.

 In this ES complex state the substrate molecule undergoes chemical change to form a product.

 It may be a splitting reaction where enzyme splits the larger substrate into smaller products or a
combining reaction where an enzyme combines two substrate molecules to form a single product
molecule. The enzyme gets separated to bind to another substrate.

Products
Substrate

Enzyme + Substrate Enzyme  substrate complex Enzyme and products

Lock and key theory

2. Induced fit theory of Koshland:

 In 1959, Koshland proposed induced fit hypothesis to account for the mode of enzyme action. 
 According to this hypothesis the enzymes are not physically rigid.
 They are flexible and can slightly alter their shape.

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 When the substrate binds to the enzyme, it induces the enzyme to alter its shape leading to a better fit
or binding between the enzyme and substrate.
 This brings about precise fitting of the substrate into the active site.

 This in turn results in the side groups of amino acids of the enzyme to have very close proximity with
certain bonds of the substrate.
 This proximity leads to stressing of particular bond or bonds, lowering the activation energy required for
breaking this bond.
 Once the bonds are broken or new bonds are formed, the products will be formed and the enzyme
dissociates from the products.

Induced fit theory

Factors affecting enzyme activity:

 The enzyme activity is influenced by a number of factors, namely, temperature, pH, enzyme
concentration, substrate concentration, product concentration, activators, poisons, inhibitors, etc.
1. Temperature:
 The enzymes function in a range of temperature and for most of the enzymes it is between 25-45C.
The velocity of enzyme reaction increases with increase in temperature upto a maximum and then
declines.
 This shows a bell shaped curve.

 The optimal temperature for most of the enzymes is 40-45 C. A high temperature denatures proteins
and inactivates the enzymes.
 At very low temperature also enzymes are temporarily inactivated.

 There are exceptions like some microorganisms which live in hot springs with temperature nearing 100
C and their enzymes are active at 90 C (e.g., Thermus aquaticus and its enzyme Taq polymerase).
 The poikilotherms undergo hibernation or aestivation to overcome extreme cold or hot conditions.

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2. pH:
The enzymes show maximum activity at a specific pH. Any variation in pH decreases enzyme activity,
e.g., pepsin acts at 1.5 to 2.0 pH in stomach and trypsin acts at pH 7.6 to 8.5 in small intestine. But
most of the enzymes show maximum activity near neutral pH 6.5 to 7.6.

3. Enzyme concentration:
 The rate of enzyme catalysed reaction increases steadily with an increase in the number of enzyme
molecules till saturation effect is reached.

4. Concentration of substrate:
 An increase in enzyme concentration increases the rate of reaction until it reaches a maximum velocity
known as Vmax when all the active sites are occupied by the substrate molecules to form enzyme
substrate complex. There is no further increase in the velocity of enzyme catalysed reaction.
 Michelis–Menten constant or Km value is defined as the substrate concentration to produce half
maximum velocity ½ Vmax in any enzyme catalysed reaction.
 This was derived independently by Michaelis and Menten (1913). Km value is constant and is
characteristic of an enzyme.
 A low Km value indicates strong affinity between enzyme and substrate, whereas a high K m value shows
weak affinity.
 The Km value for majority of the enzymes ranges between 10 to 10 moles.
5 2

5. Product concentration:
 The end product accumulation decreases the enzyme activity.

 This is because products combine with active site of enzyme and inhibit the enzyme activity.

6. Activators:
 These are factors which activate the enzymes, e.g., pepsinogen activated by HCl.


– ++ ++
Salivary amylase in activated by Cl , ATPase is activated by Mg , Ca and enolase is activated by
++
Mg .

7. Inhibitors:
 These are factors which inhibit enzyme activity temporarily or permanently, e.g., high energy radiation,
salts of heavy metals, cyanides and poisons etc.
Inhibition of enzyme action:
 The enzyme inhibitor is an organic or inorganic substance which decreases or stops catalytic activity.

 There are different types competitive, non-competitive, reversible, irreversible and allosteric.

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Effect of substrate concentration on enzyme-catalyzed reactions

(A) Competitive or reversible:

 The inhibitor closely resembles the substrate and is known as substrate analog.

 It competes with substrate and binds with active site which now not available for substrate,

e.g., Melonate, glutaric acid, oxalic acid inhibit the action of succinate dehydrogenase (SDH).

 Ethanol competes with methanol for alcohol dehydrogenase (ADH) and hence it is used for treating

methanol poisoning.

 The competitive inhibition is reversible inhibition and can be overcome by high substrate concentration.

Here Km value increases and Vmax remains unchanged.

(B) Non-competitive inhibition:

 The inhibition of enzyme activity by an inhibitor not resembling substrate.

 The inhibitor binds at a place other than active site and which impairs enzyme functioning by changing

enzyme conformation.

 Inhibitor binds with enzyme and also with ES complex.

 In this case Km value unchanged but Vmax is lowered.

E+S ES E+ P
ES + I EIS
(C) Reversible and irreversible inhibition: It is a temporary and inhibition is removed if inhibitor is
removed. In irreversible or noncompetitive inhibition a permanent change occurs, e.g., cyanide, combines
with Cu of cytochrome oxidase.
(D) Allosteric inhibition: It is a reversible non competitive inhibition. In allosteric enzymes, the inhibitors are
products or intermediates hence it is also called end product inhibition or retroinhibition or feedback
inhibition or negative modulators. The allosteric inhibitors bring about change of form of active site by
combining with allosteric sites. Hence substrates cannot bind to active sites. Glucose
6- PO4 causes allosteric inhibition of hexokinase which is a feedback allosteric inhibition. In Escherichia
coli synthesis of isoleucine is blocked by allosteric inhibition when isoleucine accumulates.

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Isoenzymes: These are enzymes showing slightly different molecular structure but having similar
catalytic enzyme sites. They show same substrate specificity but differ in their substrate affinity, activity,
maxima and regulatory controls, e.g., alcoholic dehydrogenase has four isoenzymes. Lactate
dehydrogenase has five isoenzymes.
Lactate  NAD 
Lactate dehydrogenase
 pyruvate  NADH
They differ in optimal activity and help in adaptability to changed environmental conditions. There are
more than 100 enzymes showing isoenzymes. These are developed by genetic changes.

Co-factors
Enzymes are composed of one or several polypeptide chains. However, there are a number of cases in
which non-protein constituents called cofactors are bound to the the enzyme to make the enzyme catalytically
active. In these instances, the protein portion of the enzymes is called the apoenzyme. Three kinds of cofactors
may be identified: prosthetic groups, co-enzymes and metal ions.
1. Prosthetic groups are organic compounds and are distinguished from other cofactors in that they are
tightly bound to the apoenzyme. For example, in peroxidase and catalase, which catalyze the
breakdown of hydrogen peroxide to water and oxygen, haem is the prosthetic group and it is a part of
the active site of the enzyme.
2. Co-enzymes are also organic compounds but their association with the apoenzyme is only transient,
usually occurring during the course of catalysis. Furthermore, co-enzymes serve as co-factors in a
number of different enzyme catalyzed reactions. The essential chemical components of many
coenzymes are vitamins, e.g., coenzyme nicotinamide adenine dinucleotide (NAD) and NADP contain
the vitamin niacin.

3. A number of enzymes require metal ions for their activity which form coordination bonds with side
chains at the active site and at the same time form one or more cordination bonds with the substrate,
e.g., zinc is a cofactor for the proteolytic enzyme carboxypeptidase. Catalytic activity is lost when the
co-factor is removed from the enzyme which testifies that they play a crucial role in the catalytic activity
of the enzyme.

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EXERCISE-1
1. All organic substances possess (3) Amino acids are inorganic compounds
(1) carbon and hydrogen. containing an amino group and acidic
(2) carbon, hydrogen and oxygen.
group as substituents on two different
(3) carbon, oxygen and nitrogen.
carbons
(4) carbon, hydrogen, oxygen and nitrogen.
2. The four elements making 99% of living (4) Amino acids are inorganic compounds
system are containing an amino group and acidic
(1) CHON (2) CHOP group as substituents on the same
(3) CHOS (4) CNOP carbon
3. Water is most abundant component of
7. Variety of amino acids are formed on the
organisms because
basis of
(1) it is colourless
(2) it is liquid (1) position of hydroxyl group
(3) it is universal solvent (2) position of carboxyl group
(4) it is incompressible (3) position of hydrogen
4. Which chemical characteristic is not common (4) nature of R group
to all living beings?
8. Types of amino acids found in proteins are
(1) Types of proteins present in the body
(1) 21 (2) 19
(2) Ribosomes are sites of protein synthesis
(3) Similar triplet code for amino acids (3) 20 (4) 23
(4) Energy is stored in high phosphate bonds 9. Primary structure of proteins is due to the
5. Water is the abundant substance in all presence of
organisms. Next to water, the major (1) peptide bond (2) covalent bond
component in living cells are
(3) disulphide bond (4) ionic bonds
(1) lipids (2) carbohydrates
10. In a protein structure, the first amino acid
(3) proteins (4) nucleic acids
6. Amino acids are organic compounds and are and the last amino acid are respectively
called as
called -amino acids. Why?
(1) N-terminal amino acid, C-terminal amino
(1) Amino acids are organic compounds
acid
containing an amino group and acidic
(2) C-terminal amino acid, N-terminal amino
group as substituents on two different
acid
carbons
(2) Amino acids are organic compounds (3) -amino acid, -amino acid

containing an amino group and an acidic (4) -amino acid, -amino acid

group as substituents on the same 11. The simplest amino acid is____________.
(1) glycine (2) proline
carbon
(3) leucine (4) tryptophan

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12. The charged molecule which is electrically 21. Galactose is
neutral is known as (1) triose carbohydrate (2) pentose sugar
(1) amino acid (2) zwitterion (3) hexose sugar (4) heptose sugar
(3) amide (4) peptide 22. Cellulose is formed by union of repeated
13. Quaternary structure is present in residues of
(1) haemoglobin (2) histone (1) glucose (2) fructose
(3) globulin (4) elastin (3) lipids (4) aminoacids

14. Proteins are heteropolymers, made up of: 23. Which one is a polysaccharide?
(1) Cellulose (2) Glycogen
(1) Amino acids (2) Sugars
(3) Starch (4) All the above
(3) Fatty Acids (4) Nucleic acids
24. Which one is a homopolysaccharide?
15. Each molecule of fat has
(1) Cellulose (2) Starch
(1) one glycerol molecule and three fatty acid
(3) Chitin (4) All the above
molecules.
25. Which one of the following is a
(2) two glycerol molecule and one fatty acid
homopolysaccharide?
molecule.
(1) Glycogen and inulin (2) Starch
(3) three glycerol molecules and three fatty
(3) Cellulose (4) All of these
acid molecules.
26. The stored food material found in muscles is
(4) three glycerol molecules and one fatty
(1) lipid (2) protein
acid molecule
(3) glycogen (4) phosphogen
16. Lipids are insoluble in water because lipid
27. Mannitol is
molecules are
(1) amino alcohol (2) sugar alcohol
(1) hydrophilic (2) hydrophobic
(3) amino acid (4) sugar acid
(3) neutral (4) zwitterions
28. Raffinose is a
17. A saturated fatty acid is with
(1) tetrasaccharide (2) trisaccharide
(1) low melting point (2) high melting point
(3) disaccharide (4) monosaccharide
(3) no double bond (4) both (2) and (3)
29. A polysaccharide employed in tissue culture
18. Number of fatty acids present in a molecule of
is
phospholipid is
(1) starch (2) glycogen
(1) one (2) two
(3) cellulose (4) agar-agar
(3) three (4) none
30. Lactose is composed of
19. Sugar and amino acids are :
(1) glucose + galactose
(1) Primary metabolites (2) glucose + glucose
(2) Secondary metabolites (3) glucose + fructose

(3) Feed stock (4) fructose + fructose

(4) Inoculum 31. Starch and cellulose are the compounds

made up of many units of
20. Simplest form of carbohydrate is
(1) simple sugar (2) fatty acid
(1) lactose (2) starch
(3) canesugar (4) monosaccharide (3) glycerol (4) amino acid

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32. Deoxyribose is a (3) Disulphide bond, peptide bond, hydrogen
(1) triose carbohydrate (2) pentose sugar bond.

(3) tetrose sugar (4) hexose sugar (4) Ester bond, hydrogen bond, peptide

33. Difference between RNA and DNA is that of bond.

(1) phosphate and base 40. Enzymes are basically made of

(2) sugar and base (1) vitamins (2) fats

(3) sugar and phosphate (3) proteins (4) nucleic acids

(4) all of these 41. The non-protein part of an enzyme is

34. Watson and Crick were awarded Nobel prize (1) vitamin (2) holoenzyme

for their finding of (3) apoenzyme (4) prosthetic group

(1) DNA is genetic material 42. Enzymes are sensitive to

(2) RNA is single stranded (1) rainfall (2) wind velocity

(3) DNA is double stranded (3) pH change (4) light

(4) DNA guides mRNA synthesis 43. In high temperature, enzymes are

35. DNA is composed of repeating units of (1) inactivated (2) killed

(1) deoxyribonucleosides (3) highly effective (4) denatured

(2) deoxyribonucleotides 44. Which is not a trait of enzymes?

(3) ribonucleosides (1) Specific in nature

(4) ribonucleotides. (2) Proteinaceous nature

36. The two strands of DNA are (3) Used up in reaction

(1) similar and parallel (4) Speed up rate of biochemical reaction

(2) similar and antiparallel 45. A coenzyme is

(3) complimentary and parallel (1) one that shares function of another

(4) complementary and antiparallel enzyme.

37. Number of base pairs in each turn of B-DNA (2) same enzyme found in different organs or

helix is tissues.

(1) 10 (2) 11 (3) organic or inorganic group that is

essential for enzyme activity.
(3) 12 (4) variable
(4) organic nonproteinaceous group that is
38. RNA doesnot possess
essential for enzyme activity.
(1) uracil (2) thymine
46. Enzymes are polymers of
(3) adenine (4) cytosine
(1) fatty acids
39. Which of the following bonds are found in
(2) amino acids.
DNA?
(3) hexose sugar
(1) Peptide bond, N-glycosidic bond, ester
bond. (4) inorganic phosphate

(2) N-glycosidic bond, hydrogen bond,

phosphodiester bond.
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47. At low temperature an enzyme is 56. Enzymes show maximum activity at :
(1) slightly activated (2) denatured (1) Low temperature
(3) coagulated (4) inactivated
(2) High temperature
48. A non protein organic part attached firmly to
(3) Optimum temperature
apoenzyme is called
(1) cofactor (2) activator (4) all of the above

(3) prosthetic group (4) coenzyme 57. Enzymes are required in traces because they
49. An enzyme acts as catalyst because
(1) have high turnover number
(1) it accelerates the chemical reaction
(2) remain unused at the end of reaction and
(2) it remain unchanged
are reused
(3) enzyme catalysed reactions are
reversible (3) show cascade effect
(4) All correct (4) all correct
50. Coenzyme is
58. Enzymes with same function (property) and
(1) inorganic metal activator
different molecular structure are called
(2) non-protein organic part attached firmly
(3) non-protein organic part attached loosely (1) zymases

(4) vitamin A (2) isomerases

51. Enzymes are
(3) isoenzymes
(1) living (2) non living
(4) coenzymes
(3) both (4) none
+
52. NADP is 59. Coenzyme in enzyme determines
(1) coenzyme (2) an enzyme (1) specificity (2) catalytic activity
(3) part of tRNA. (4) all the above
(3) structure (4) all of these
53. The activity of an enzyme is affected by
(1) pH 60. Site of enzyme synthesis in a cell is
(2) temperature (1) Ribosomes (2) RER
(3) the presence or absence of cofactors
(3) Golgi complex (4) All of these
(4) all of the above.
54. Apoenzyme is 61. Which of the following is without coenzyme

(1) protein (2) carbohydrate activity?

(3) vitamin (4) amino acid (1) Thiamine (2) Riboflavin

55. Most of the digestive enzymes belong to the
(3) Protein (4) Vitamin E
class of
62. Enzyme Hexokinase requires
(1) lyases
(2) hydrolases (1) Mo (2) Mn
(3) transferases (3) K (4) Mg
(4) oxidoreductases

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EXERCISE-2
1. Give the correct sequence of elements in 8. Number of essential amino acids in humans is
human body according to their decreasing dry (1) 6 (2) 9
weight (3) 10 (4) 14
(1) Carbon, oxygen, nitrogen 9. Select the essential amino acid

(2) Oxygen, carbon, nitrogen (1) Serine (2) Aspartic acid

(3) Nitrogen, carbon, oxygen (3) Glycine (4) Phenylalanine

10. Nitrogen bases are
(4) Nitrogen, oxygen, carbon
(1) heterocyclic
2. Select the simplest amino acid from the
(2) homocyclic
following
(3) open chain hydrocarbons
(1) Alanine (2) Asparagine
(4) all the above
(3) Glycine (4) Tyrosine
11. Inulin is a polymer of
3. Relation between aminoacid and protein is
(1) arabinose (2) glucose
similar to the one found between
(3) galactose (4) fructose
(1) thymine and uracil 12. Select the monosaccharide pair from the
(2) glucose and fructose following
(3) nucleotides and nucleic acid (1) Glucose and fructose
(4) nucleosides and nucleic acids (2) Ribose and maltose
4. Select the non-essential amino acid from the (3) Glucose and sucrose
following (4) Ribose and sucrose.
(1) Methionine (2) Lysine 13. Select the following groups containing
(3) Leucine (4) Alanine polysaccharides
5. Enormous diversity of protein molecules is (1) Sucrose, glucose and fructose
due to (2) Glycogen, cellulose and starch

(1) peptide bonds (3) Glycogen, sucrose and maltose

(4) Maltose, lactose and fructose
(2) amino groups of amino acids
14. Carbohydrates have many functions in the
(3) R-groups of amino acids
cell. Which of the following is an incorrect
(4) sequence of amino acids
match of the carbohydrate with its functions?
6. Which one of the following is a fibrous
(1) Disaccharides - sugar transport in plants
protein?
(2) Starches - energy storage in plants
(1) Haemoglobin (2) Globulin
(3) Lactose - energy storage in plants
(3) Collagen (4) Albumin
(4) Glucose - sugar transport in humans
7. Select the one which consists of essential 15. From the following groups, select the group in
amino acids. which all the three are examples of
(1) Leucine and glycine polysaccharides
(2) Lysine and phenylalanine (1) Starch, glycogen, cellulose
(3) Tryptophan and glutamic acid (2) Sucrose, maltose, glucose
(4) Valine and Glycine (3) Glucose, fructose, lactose
(4) Galactose, starch, sucrose

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16. The smallest storage polysaccharide is 24. In cell, digestive enzymes are found mainly in
(1) inulin (2) dextrose (1) lysozymes (2) lysosomes
(3) amylose (4) amylopectin (3) ribosomes (4) lomasomes
17. Purines are 25. Nucleotides
(1) open chain structures (1) contain a sugar, a nitrogen base and a
(2) single ring structures phosphate molecule
(3) double ring structures (2) are the monomers of the polysaccharides
(4) open chain with alternate double bonds (3) join together by covalent bonding
18. DNA is made of between bases
(1) pentose sugar, purines and pyrimidines (4) are found in DNA, RNA and proteins
(2) phosphoric acid, pentose sugar and 26. From the following findout which pertains to a
pyrimidines RNA nucleotide and not to a DNA molecule?
(3) pentose sugar, phosphoric acid and (1) Contains the sugar ribose
purines (2) Contains a nitrogen containing base
(4) pentose sugar, phosphoric acid, purines (3) Contains a phosphate molecule
and pyrimidines (4) Becomes bonded to other nucleotides
19. Purine bases of DNA are 27. DNA occurs in
(1) A and U (2) A and G (1) nucleus only
(3) A and C (4) C and T (2) cytoplasm
20. Give the correct order of three molecules that (3) cell organelles
make up a nucleotide (4) nucleus and some cell organelles.
(1) Pentose sugar-nitrogen base-phosphate 28. Prokaryotes possess
(2) Phosphate-pentose sugar-nitrogen base (1) DNA and RNA, no ribosomes
(3) Nitrogen base-phosphate-pentose sugar (2) Ribosomes and DNA, no RNA
(4) phosphate-hexose sugar-nitrogen base (3) Ribosomes, DNA and RNA
21. In AGCT of DNA, hydrogen bonds and base (4) Do not possess ribosomes, DNA and
pairings occur between RNA
(1) A - G, C - T (2) A - C, G - T 29. Enzymes with two sites are called
(3) A - T, C - G (4) A - U, C - G (1) apoenzyme
22. Enzymes are absent in (2) holoenzyme
(1) bacteria (2) cyanobacteria (3) allosteric enzyme
(3) viruses (4) RBC (4) conjugate enzyme
23. A nucleoside is formed of 30. Which of the following bond formed by
(1) pentose sugar and phosphate dehydration?
(2) phosphate and nitrogen base (1) Peptide bond and hydrogen bond
(3) pentose sugar and nitrogen base (2) Peptide bond and glycosidic bond
(4) pentose sugar, phosphate and nitrogen (3) Glycosidic bond and hydrogen bond
base (4) all of A, B, C

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31. ATP is a 38. Combination of apoenzyme and coenzyme
(1) nucleotide (2) nucleosome produces
(3) nucleoside (4) purine (1) holoenzyme
32. Biological organisation starts with (2) prosthetic group
(1) cellular level (3) enzyme - product complex
(2) organism level (4) enzyme - substrate complex
(3) atomic level
39. Which of the following is correct in an
(4) submicroscopic molecular level
enzyme-controlled reaction?
33. An enzyme made of both protein and non-
(1) E  S EP
protein parts is together called
(1) holoenzyme (2) coenzyme (2) E  S ES 
 EP
(3) endoenzyme (4) exoenzyme
(3) E  S ES E
34. Checking of an enzyme action by blocking its
active site is called (4) E  S P E P
(1) allosteric inhibition 40. Which of the following has co-enzyme
(2) feedback inhibition activity?
(3) competitive inhibition
(1) Purine (2) Pyrimidine
(4) non-competitive inhibition
(3) Nicotinamide (4) All
35. An enzyme accelerates a biochemical
41. Which part of enzyme in a holoenzyme
reaction by
determines specificity of enzyme?
(1) production of heat
(1) Apoenzyme (2) Prosthetic group
(2) increasing substrate movements
(3) Meta activator (4) None of these
(3) changing free enzyme
42. Which of the following is a coenzyme?
(4) lowering energy of activation
(1) NAD (2) Ligase
36. Temperature is increased from 3 to 40C.
++
The rate of enzyme controlled biochemical (3) Fe (4) All

reaction will 43. Which determines specificity of enzyme?

(1) increase (1) Protein part (2) Coenzyme

(2) decrease (3) Full holoenzyme (4) Inorganic factor
(3) increase initially and then decrease 44. At - 4C, enzymes become
(4) not change (1) slightly inactive (2) inactivated
37. Competitive inhibition is due to
(3) killed (4) unaffected
(1) nonavailability of activation energy
45. Competitive inhibitors are those which
(2) short wave radiation
(1) alter the structure of enzyme molecule
(3) substrate analogue
(2) act as coenzyme for the reaction
(4) protein poison
(3) compete for same active site of enzyme

(4) (1) and (3)

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46. The enzymes are highly specific in their 52. Identify the given structure and name the
action. This specificity of an enzyme is due to compound.
(1) active site
(2) arrangement of amino acids
(3) specific coenzyme
(4) RNA
47. Which inactivates an enzyme by occupying its
active site?
(1) Ribose, Glucose
(1) Competitive inhibitor
(2) Deoxyribose, Ribose
(2) Allosteric inhibitor
(3) Noncompetitive inhibitor (3) Glucose, Ribose

(4) All of these (4) Ribose, Deoxyribose

48. A substance unrelated to substrate but 53. The R-group in proteinaceous amino acid

capable of reversibly changing activity of makes them different. Name the amino acids

enzyme by binding to a site other than active A-C correctly according to the R groups given

site is called in each structure.

(1) catalytic inhibitor

(2) allosteric modulator / inhibitor
(3) competitive inhibitor
(4) non-competitive inhibitor
49. Ribozyme is
(1) RNA without sugar
(2) RNA with extra phosphate
(3) RNA with enzyme activity
(4) RNA without phosphate
(1) A-Glycine, B-Serine, C-Alanine
50. Enzymes exist in the cells as
(2) A-Alanine, B-Glycine, C-Serine
(1) solid (2) crystals
(3) A-Serine, B-Glycine, C-Alanine
(3) colloid (4) liquid
51. Identify the zwitter ionic form in the given (4) A-Serine, B-Alanine, C-Glycine

reversible reaction. 54. The sugars found in polynucleotides are

A B
(1) ribose - sucrose
(2) 2' deoxyribose - ribose
(3) ribose - dextrose
(4) deoxyribose - ribulose

Choose the correct option

(1) A (2) C
(3) B (4) None of these

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55. The steps in catalytic cycle of an enzyme 57. Find out the correct match.
action are given in random order. (1) Inulin - Polymer of glucose
(i) The enzyme releases the products. Now (2) Starch - Spiral secondary structure
enzyme is free to bind another substrate. (3) Cellulose - Component of cell wall
(ii) The active sites, now in close proximity of (4) Glycogen - Monosaccharide and reserved
substrate breaks the bond of substrate food of plants
and forms E-P complex.
58. Assertion : In a DNA molecule, A-T rich parts
(iii) Binding of substrate induces the enzyme melt before G-C rich parts.
to alter its shape fitting more tightly
Reason : In between A and T there are three
around the substrate.
H-bond, whereas in between G and C there
(iv) The substrate binds to the active site of are two H- bonds.
enzyme (i.e., fitting into the active site).
(1) If both Assertion and Reason are true and
The correct order is the Reason is the correct explanation of
(1) (i), (ii), (iii), (iv) the Assertion.
(2) (iv), (iii), (ii), (i) (2) If both Assertion and Reason are true but
(3) (i), (iii), (ii), (iv) the Reason is not the correct explanation
(4) (i), (ii), (iv), (iii) of the Assertion.

56. Match the biomoecules given in column I with (3) If Assertion is true but Reason is false.
their examples given in column II and choose (4) If both Assertion and Reason are false.
the correct answer. 59. Assertion : The amino acid glycine comes
Column - I Column - II under the category of nonessential amino
(Biomolecules) (Examples) acids.

A. Carbohydratess I. Trypsin Reason : This is due to the fact that it is

B. Protein II. Cholesterol synthesised in the body.

C. Nucleic acid III. Inulin (1) If both Assertion and Reason are true and
the Reason is the correct explanation of
D. Lipid IV. Adenylic acid
the Assertion.
(1) A-III ; B-I ; C-IV ; D-II
(2) If both Assertion and Reason are true but
(2) A-II ; B-III ; C-IV ; D-I
the Reason is not the correct explanation
(3) A-III ; B-IV ; C-I ; D-II
of the Assertion.
(4) A-IV ; B-I ; C-III ; D-III
(3) If Assertion is true but Reason is false.
(4) If both Assertion and Reason are false.

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 BIOMOLECULES

EXERCISE-3
1. Three of the following statements about
enzymes are correct and one is wrong. Which
one is wrong? [AIPMT - 2010]
(1) Enzymes require optimum pH for
maximal activity X-axis Y-axis
(2) Enzymes are denatured at high (1) enzymatic - activity pH
temperature but in certain exceptional (2) temperature - enzyme activity
organisms they are effective even at (3) substrate concentration- enzymatic activity
temperatures 80° 90° C (4) enzymatic activity - temperature
(3) Enzymes are highly specific 4. Which one of the following structural formulae
(4) Most enzymes are proteins but some are of two organic compounds is correctly
lipids identified along with its related function?
2. The figure given below shows the conversion [AIPMT - 2011]
of a substate into product by an enzyme. In
which one of the four options (ad) the
components of reaction labelled as A, B, C
and D are identified correctly?[AIPMT - 2010]

(1) B : Adenine - A nucleotide that makes up

nucleic acids
(2) A : Triglyceride - Major source of energy
A B C D (3) B : Uracil - A component of DNA
(1) Potential Transition Activation Activation
(4) A : Lecithin - A component of cell
energy state energy with energy without
enzyme enzyme membrane
(2) Transition potential Activation Activation 5. Which one out of A – D given below correctly
state energy energy energy with
without enzyme
represents the structural formula of the basic
enzyme amino acid? [AIPMT - 2012]
(3) Potential Transition Activation Activation
energy state energy with energy without
enzyme enzyme
(4) Activation Transition Activation Potential
energy with state energy energy
enzyme enzyme without

3. The curve given below shows enzymatic

activity in relation to three conditions (pH,
temperature and substrate concentration). (1) C (2) D
What do the two axes (x and y) represent? (3) A (4) B
[AIPMT - 2011]

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 BIOMOLECULES
6. Which one is the most abundant protein in the (1) Lecithin – phosphorylated glyceride found
animal world? [AIPMT - 2012] in cell membrane.
(1) Trypsin (2) Haemoglobin (2) Palmitic acid – unsaturated fatty acid with
(3) Collagen (4) Insulin 18 carbon atoms.

7. The given diagrammatic representation (3) Adenylic acid – adenosine with a glucose
phosphate molecule.
shows one of the categories of small
(4) Alanine amino acid – contains an amino
molecular weight organic compounds in the
group and an acidic group anywhere in
living tissues. Identify the category shown and
the molecule.
the one blank component “X” in it.
10. A phosphoglyceride is always made up of
[AIPMT 2012]
[NEET - 2013]
(1) a saturated or unsaturated fatty acid
esterified to a glycerol molecule to which
a phosphate group is also attached.
(2) a saturated or unsaturated fatty acid
esterified to a phosphate group which is
Category Component
also attached to a glycerol molecule.
(1) Cholesterol - Guanine
(3) only a saturated fatty acid esterified to a
(2) Amino acid - NH2
glycerol molecule to which a phosphate
(3) Nucleotide - Adenine
group is also attached.
(4) Nucleoside - Uracil
(4) only an unsaturated fatty acid esterified to
8. Which one of the following is wrong
a glycerol molecule to which a phosphate
statement? [AIPMT - 2012]
group is also attached.
(1) Anabaena and Nostoc are capable of
11. Macromolecule chitin is - [NEET - 2013]
fixing nitrogen in free living state also.
(1) sulphur containing polysaccharide
(2) Root nodule forming nitrogen fixers live as
(2) simple polysaccharide
aerobes under free living conditions.
(3) nitrogen containing polysaccharide
(3) Phosphorus is a constituent of cell
(4) phosphorous containing polysaccharide
membranes, certain nucleic acids and all
12. Transition state structure of the substrate
proteins.
formed during an enzymatic reaction is -
(4) Nitrosomonas and Nitrobacter are
[NEET - 2013]
chemoautotrophs.
(1) transient and unstable
Ans. (3)
(2) permanent and stable
Sol. Phosphorus is present in plasma membrane
(3) transient but stable
in the form of phospholipid bilayer. It is an
(4) permanent but unstable
essential component of all nucleic acids not
13. The essential chemical components of many
„certain‟ nucleic acids. Moreover, phosphorus
coenzymes are - [NEET - 2013]
is never found in proteins.
9. Which one of the following biomolecules is (1) carbohydrates (2) vitamins

correctly characterized? [AIPMT - 2012] (3) proteins (4) nucleic acids

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 BIOMOLECULES
14. Which of the following statements about 19. The chitinous exoskeleton of arthropods is
enzymes is wrong? [NEET - 2013] formed by the polymerisation of[AIPMT-2015]
(1) Enzymes are denatured at high (1) N acetyl glucosamine
temperatures. (2) lipoglycans
(2) Enzymes are mostly proteins but some
(3) keratin sulphate and chondroitin sulphate
are lipids also.
(4) D glucosamine
(3) Enzymes are highly specific.
20. Which of the following biomolecules does
(4) Enzymes require optimum pH and
have a phosphodiester bond? [AIPMT-2015]
temperature for maximum activity.
15. Uridine, present only in RNA is a [NEET-2013] (1) Amino acids in a polypeptide

(1) nucleoside (2) nucleotide (2) Nucleic acids in a nucleotide

(3) purine (4) pyrimidine (3) Fatty acids in a diglyceride

16. The figure shows a hypothetical tetrapeptide (4) Monosaccharides in a polysaccharide
portion of a protein with parts labelled AD. 21. Which one of the following statements is
Which one of the following options is correct?
incorrect? [AIPMT - 2015]
[NEET - 2013]
CH
(1) The competitive inhibitor does not affect
CH2 – COOH
the rate of breakdown of the enzyme
SH CH2
substrate complex.
CH2OH CH2 CH2 CH2

–HN – CH – CO – NH – CH – CO – NH – CH – CO – HN – CH – CO– (2) The presence of the competitive inhibitor

A B C D

(1) D is the acidic amino acid glutamic acid. decreases the Km of the enzyme for the
(2) C is an aromatic amino acid tryptophan. substrate.
(3) A is the C terminal amino acid and D is N
terminal amino acid. (3) A competitive inhibitor reacts reversibly
(4) A is a sulphur containing amino acid with the enzyme to form an enzyme
methionine.
inhibitor complex.
17. Select the option which is not correct with
respect to enzyme action. [AIPMT - 2014] (4) In competitive inhibition, the inhibitor
(1) Substrate binds with enzyme at its active
molecule is not chemically changed by
site.
(2) Addition of lot of succinate does not the enzyme.
reverse the inhibition of succinic
22. A non proteinaceous enzyme is-[NEET-2016]
dehydrogenase by malonate.
(1) lysozyme
(3) A noncompetitive inhibitor binds the
(2) ribozyme
enzyme at a site distinct from that which
binds the substrate. (3) ligase
(4) Malonate is a competitive inhibitor of (4) deoxyribonuclease.
succinic dehydrogenase. 23. Which of the following is the least likely to be
18. Which one of the following is a non reducing involved in stabilising the three dimensional
folding of most proteins? [NEET - 2016]
carbohydrate? [AIPMT - 2014]
(1) Hydrogen bonds
(1) Maltose (2) Sucrose (2) Electrostatic interaction
(3) Lactose (4) Ribose 5phosphate (3) Hydrophobic interaction
(4) Ester bonds

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 BIOMOLECULES
24. Which of the following describes the given (1) Proteins (2) Polysaccharides
graph correctly? [NEET - 2016] (3) Lipids (4) Nucleic acids
29. The two functional groups characteristic of
sugars are [NEET - 2018]
(1) Hydroxyl and methyl
(2) Carbonyl and methyl
(3) Carbonyl and hydroxyl
(1) Endothermic reaction with energy A in
(4) Carbonyl and phosphate
presence of enzyme and B in absence of
30. Consider the following statement:
enzyme.
(2) Exothermic reaction with energy A in [NEET-2019]

presence of enzyme and B in absence of (A) Coenzyme or metal ion that is tightly

enzyme. bound to enzyme protein is called

(3) Endothermic reaction with energy A in prosthetic group.
absence of enzyme and B in presence of (B) A complete catalytic active enzyme with
enzyme. its bound prosthetic group is called
(4) Exothermic reaction with energy A in apoenzyme.
absence of enzyme and B in presence of Select the correct option.
enzyme. (1) (A) is true but (B) is false.
25. A typical fat molecule is made up of (2) Both (A) and (B) are false.
[NEET - 2016] (3) (A) is false but (B) is true.
(1) one glycerol and one fatty acid molecule (4) Both (A) and (B) are true.
(2) three glycerol and three fatty acid 31. Identify the basic amino acid from the
molecules following [NEET - 2020]
(3) three glycerol molecules and one fatty
(1) Tyrosine (2) Glutamic Acid
acid molecule
(3) Lysine (4) Valine
(4) one glycerol and three fatty acid
molecules 32. Identify the substances having glycosidic

26. Which one of the following statements is bond and peptide bond, respectively in their
wrong? [NEET - 2016] structure : [NEET - 2020]
(1) Uracil is a pyrimidine (1) Chitin, cholesterol (2) Glycerol, trypsin
(2) Glycine is a sulphur containing amino (3) Cellulose, lecithin (4) Inulin, insulin
acid
33. Which of the following are not secondary
(3) Sucrose is a disaccharide
metabolites in plants? [NEET - 2021]
(4) Cellulose is a polysaccharide
27. Which of the following statements is correct (1) Rubber, gums (2) Morphine, codeine

with reference to enzymes? [NEET - 2017] (3) Amino acids, glucose

(1) Holoenzyme = Apoenzyme + Coenzyme (4) Vinblastin, curcumin
(2) Coenzyme = Apoenzyme + Holoenzyme 34. Identify the incorrect pair - [NEET - 2021]
(3) Holoenzyme = Coenzyme + Cofactor (1) Drugs - Ricin
(4) Apoenzyme = Holoenzyme + Coenzyme (2) Alkaloids - Codeine
28. Which of the following are not polymeric?
(3) Toxin - Abrin
[NEET - 2017]
(4) Lectins - Concanavalin A

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 BIOMOLECULES
35. Match List-I with List-II : [NEET - 2021] Choose the correct answer from the options
List - I List - II given below :
(a) Protein (i) C = C double bonds (1) a, b and c only (2) a, d and e only
(b) Unsaturated (3) c, d and e only (4) a, b and d only
fatty acid (ii) Phosphodiester 40. Given below are two statements :
bonds [NEET - 2023]
(c) Nucleic acid (iii) Glycosidic bonds Statement I : A protein is imagined as a line,
(d) Polsyaccharide (iv) Peptide bonds the left end represented by first amino acid
Choose the correct answer from the options (C-terminal) and the right end represented by
given below : last amino acid (Nterminal).
(a) (b) (c) (d) Statement II : Adult human haemoglobin,
(1) (iv) (iii) (i) (ii) consists of 4 subunits (two subunits of  type
(2) (iv) (i) (ii) (iii) and two subunits  type.)
(3) (i) (iv) (iii) (ii) In the light of the above statements, choose
(4) (ii) (i) (iv) (iii) the correct answer from the options given
36. A dehydration reaction links two glucose below :
molecules to produce maltose. If the formula (1) Both statement I and Statement II are false.
for glucose is C6 H12 O6 then what is the (2) Statement I is true but Statement II is false.
formula for maltose? [NEET - 2022] (3) Statement I is false but Statement II is true.
(1) C12 H20 O10 (2) C12 H24 O12 (4) Both statement I and Statement II are true.
(3) C12 H22 O11 (4) C12 H24 O11 41. Given below are two statements :
37. Match List-I with List-II [NEET - 2022] [NEET - 2023]
List - I List - II Statement I : Low temperature preserves the
(Biological Molecules) (Biological enzyme in a temporarily inactive state
Functions) whereas high temperature destroys
(a) Glycogen (i) Hormone enzymatic activity because proteins are
(b) Globulin (ii) Biocatalyst denatured by heat.
(c) Steroids (iii) Antibody Statement II : When the inhibitor closely
(d) Thrombin (iv) Storage resembles the substrate in its molecular
product structure and inhibits the activity of the
Choose the correct answer from the options enzyme, it is known as competitive inhibitor.
given below : In the light of the above statements, choose
(1) (a - iii), (b - ii), (c - iv), (d - i) the correct answer from the options given
(2) (a - iv), (b - ii), (c - i), (d - iii) below :
(3) (a - ii), (b - iv), (c - iii), (d - i) (1) Both Statement I and Statement II are
(4) (a - iv), (b - iii), (c - i), (d - ii) false.
38. Exoskeletion of arthropods in composed of: (2) Statement I is true but Statement II is
[NEET - 2022] false.
(1) Cutin (2) Cellulose (3) Statement I is false but Statement II is
(3) Chitin (4) Glucosamine true.
39. Read the following statements on lipids and (4) Both Statement I and Statement II are
find out correct set of statements : true.
[NEET - 2022]

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 BIOMOLECULES

ANSWERS
EXERCISE - 1
1. (1) 2. (1) 3. (3) 4. (1) 5. (3) 6. (2) 7. (4)

8. (3) 9. (1) 10. (4) 11. (1) 12. (2) 13. (1) 14. (1)

15. (1) 16. (2) 17. (4) 18. (2) 19. (1) 20. (4) 21. (3)

22. (1) 23. (4) 24. (4) 25. (4) 26. (3) 27. (2) 28. (2)

29. (4) 30. (1) 31. (1) 32. (2) 33. (2) 34. (3) 35. (2)

36. (4) 37. (1) 38. (2) 39. (2) 40. (3) 41. (4) 42. (3)

43. (4) 44. (3) 45. (4) 46. (2) 47. (4) 48. (3) 49. (4)

50. (3) 51. (2) 52. (1) 53. (4) 54. (1) 55. (2) 56. (3)

57. (4) 58. (3) 59. (2) 60. (4) 61. (3) 62. (4)

EXERCISE - 2
1. (2) 2. (3) 3. (3) 4. (4) 5. (4) 6. (3) 7. (2)

8. (2) 9. (4) 10. (1) 11. (4) 12. (1) 13. (2) 14. (3)

15. (1) 16. (1) 17. (3) 18. (4) 19. (2) 20. (2) 21. (3)

22. (3) 23. (3) 24. (2) 25. (1) 26. (1) 27. (4) 28. (3)

29. (3) 30. (2) 31. (1) 32. (4) 33. (1) 34. (3) 35. (4)

36. (3) 37. (3) 38. (1) 39. (2) 40. (3) 41. (1) 42. (1)

43. (1) 44. (2) 45. (3) 46. (1) 47. (1) 48. (4) 49. (3)

50. (3) 51. (3) 52. (3) 53. (2) 54. (2) 55. (2) 56. (1)

57. (3) 58. (3) 59. (1)

EXERCISE - 3
1. (4) 2. (2) 3. (2) 4. (4) 5. (2) 6. (3) 7. (4)

8. (3) 9. (1) 10. (1) 11. (3) 12. (1) 13. (2) 14. (2)

15. (1) 16. None of the options is correct. 17. (2) 18. (2) 19. (1)

20. (2) 21. (2) 22. (2) 23. (4) 24. (2) 25. (4) 26. (2)

27. (1) 28. (3) 29. (3) 30. (2) 31. (3) 32. (4) 33. (3)

34. (1) 35. (2) 36. (2) 37. (4) 38. (3) 39. (3) 40. (3)

41. (4)

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