CH.RAGHAVA RAO, S.D.

C Pu college, Bangarpet,Kolar Ph:7411224133

Biomolecules
Living systems are made up of various complex biomolecules like carbohydrates, proteins, nucleic acids, lipids,
etc. Proteins and carbohydrates are essential constituents of our food. These biomolecules interact with each
other and constitute the molecular logic of life processes.
Carbohydrates:
Carbohydrates are primarily produced by plants and form a very large group of naturally occurring organic
compounds. Most of them have a general formula, Cx(H2O)y.Chemically, the carbohydrates may be defined as
optically active polyhydroxy aldehydes or ketones or the compounds which produce such units on
hydrolysis. Some of the carbohydrates, which are sweet in taste, are also called sugars. Carbohydrates are also
called saccharides (Greek: sakcharon means sugar).
Classification of Carbohydrates:
Carbohydrates are classified on the basis of their behaviour on hydrolysis. They have been broadly divided into
following three groups.
(i) Monosaccharides: A carbohydrate that cannot be hydrolysed further to give simpler unit of polyhydroxy
aldehyde or ketone is called a monosaccharide. About 20 monosaccharides are known to occur in nature.
Ex: Glucose, fructose, ribose, etc.
(ii) Oligosaccharides: Carbohydrates that yield two to ten monosaccharide units, on hydrolysis, are called
oligosaccharides. They are further classified as disaccharides, trisaccharides, tetrasaccharides, etc., depending
upon the number of monosaccharides, they provide on hydrolysis.
Amongst these the most common are disaccharides. The carbohydrates on hydrolysis form two same or
different monosaccharide units are called disaccharide.
Ex: Sucrose on hydrolysis gives one molecule of glucose and one molecule of fructose
Maltose gives two molecules of only glucose.
(iii) Polysaccharides: Carbohydrates which yield a large number of monosaccharide units on hydrolysis are
called polysaccharides. Polysaccharides are not sweet in taste, hence they are also called non-sugars.
Ex: Starch, cellulose, glycogen, gums, etc.
The carbohydrates may also be classified as either reducing or nonreducing sugars.
The carbohydrates which reduce Fehling’s solution and Tollens’ reagent are referred to as reducing sugars.
Ex: All mono saccharides (aldose or ketose), Maltose, lactose etc
The carbohydrates which not reduce Fehling’s solution and Tollens’ reagent are referred to as Non reducing
sugars.
Ex: Sucrose
Monosaccharides:
Monosaccharides are further classified on the basis of number of carbon atoms and the functional group
present in them.
If a monosaccharide contains an aldehyde group, it is known as an aldose. Further they are classified into
aldotriose, aldotetrose, aldopentose, aldohexose etc.
If a monosaccharide contains an ketone group, it is known as an ketose. Further they are classified into
Ketotriose, Ketotetrose, Ketopentose, Ketohexose etc.
Glucose:
Glucose occurs freely in nature as well as in the combined form. It is present in sweet fruits and honey. Ripe
grapes also contain glucose in large amounts. It is prepared as follows:
Preparation of Glucose:
1. From sucrose: (Cane sugar): If sucrose is boiled with dilute HCl or H 2SO4 in alcoholic solution, glucose and
fructose are obtained in equal amounts.
𝐻+(𝑜𝑟)
C12H22O11 + H2O > C6H12O6 + C6H12O6
𝐼𝑛𝑣𝑒𝑟𝑡𝑎𝑠𝑒
Sucrose Glucose Fructose
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133
2. From starch: Commercially glucose is obtained by hydrolysis of starch by boiling it with dilute H 2SO4 at
𝐻+(𝑜𝑟)
393 K under pressure. (C6H10O5 )n + nH2O 𝐴𝑚𝑦𝑙𝑎𝑠𝑒> n C6H12O6
Starch or cellulose Glucose
Structure of Glucose:
Glucose is an aldohexose and is also known as dextrose. It is the monomer of many of the larger
carbohydrates, namely starch, cellulose. It is probably the most abundant organic compound on earth. It was
assigned the structure given below on the basis of the following evidences:
1. Its molecular formula was found to be C6H12O6.
2. Glucose On prolonged heating with HI, it forms n-hexane, suggesting that all the six carbon atoms are
linked in a straight chain.

3. Glucose reacts with hydroxylamine to form an oxime and adds a molecule of hydrogen cyanide to give
cyanohydrin. These reactions confirm the presence of a carbonyl group (>C = O) in glucose.

4. Glucose undergo oxidation with mild oxidising agent like bromine water form Gluconic acid (six carbon
carboxylic acid). This indicates that the carbonyl group is present as an aldehydic group.

5. Glucose undergo acetylation with acetic anhydride gives glucose pentaacetate which confirms the
presence of five –OH groups. Since it exists as a stable compound, five –OH groups should be attached to
different carbon atoms.

6. Glucose and Gluconic acid On oxidation with nitric acid, form dicarboxylic acid, saccharic acid. This
indicates the presence of a primary alcoholic (–OH) group in glucose.

The exact spatial arrangement of different —OH groups was given by Fischer after studying many other
properties.
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133
Glucose is correctly named as D(+)-glucose. ‘D’ before the name of glucose represents the configuration
whereas ‘(+)’ represents dextrorotatory nature of the molecule. (‘D’ and ‘L’ have no relation with the optical
activity of the compound indicate the relative configuration of a particular stereoisomer of a compound with
respect to configuration of some other compound).
In the case of carbohydrates, this refers to their relation with a particular isomer of glyceraldehyde.
Glyceraldehyde contains one asymmetric carbon atom and exists in two enantiomeric forms as shown below.

(+) Isomer of glyceraldehyde has ‘D’ configuration. The –OH group lies on right hand side in the structure. All
those compounds which can be chemically correlated to D (+) isomer of glyceraldehyde are said to have
D-configuration whereas those which can be correlated to ‘L’ (–) isomer of glyceraldehyde are said to have
L—configuration. In L (–) isomer –OH group is on left hand side.
For assigning the configuration of monosaccharides, it is the lowest asymmetric carbon atom is compared.

As in (+) glucose, —OH on the lowest asymmetric carbon is on the right side which is comparable to (+)
glyceraldehyde, so (+) glucose is assigned D-configuration. Other asymmetric carbon atoms of glucose are not
considered for this comparison. Also,the structure of glucose and glyceraldehyde is written in a way that most
oxidised carbon (in this case –CHO)is at the top.
Cyclic Structure of Glucose:
The open chain structure of glucose explained most of its properties but the following reactions could not be
explained by this structure.
1.Glucose having the aldehyde group, but it does not give Schiff’s test and it does not form hydrogensulphite
product with NaHSO3 .
2. The pentaacetate of glucose does not react with hydroxylamine indicating the absence of free -CHO group.
3. Glucose is found to exist in two different crystalline forms which are named as α and β.
The α-form of glucose (m.p. 419 K) is obtained by crystallisation from conc solution of glucose at 303 K.
The β-form (m.p. 423 K) is obtained by crystallisation from hot and saturated aqueous solution at 371 K.
This behaviour could not be explained by the open chain structure for glucose. It was proposed that one of the
—OH groups may add to the —CHO group and form a cyclic hemiacetal structure. It was found that glucose
forms a six-membered ring in which —OH at C-5 is involved in ring formation. This explains the absence of
—CHO group and also existence of glucose in two forms. These two cyclic forms exist in equilibrium with
open chain structure.

The two cyclic hemiacetal forms of glucose differ only in the configuration of the hydroxyl group at C1, called
anomeric carbon. So α-form and β-form, are called C1anomers.
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133
The six membered cyclic structure of glucose is called pyranose structure (α– or β–), in analogy with pyran.
Pyran is a cyclic organic compound with one oxygen atom and five carbon atoms in the ring.
Fructose:
Fructose is an important ketohexose. It is obtained along with glucose by the hydrolysis of disaccharide,
sucrose. It is a natural monosaccharide found in fruits, honey and vegetables. In its pure form it is used as a
sweetner.
Structure of Fructose:
Fructose also has the molecular formula C6H12O6 and on the basis of its reactions it was found to contain a
ketonic functional group at carbon number 2 and six carbons in straight chain as in the case of glucose. It
belongs to D-series and is a laevorotatory compound. It is appropriately written as D-(–)-fructose. Its open
chain structure is

It also exists in two cyclic forms which are obtained by the addition of —OH at C5 to the (C = O) group. The
ring, thus formed is a five membered ring and is named as furanose with analogy to the compound furan.
Furan is a five membered cyclic compound with one oxygen and four carbon atoms.
The cyclic structures of two anomers of fructose are represented by Haworth structures as given.

Disaccharides:
Disaccharides on hydrolysis with dilute acids or enzymes yield two molecules of either the same or different
monosaccharides. The two monosaccharides are joined together by an oxide linkage formed by the loss of a
water molecule. The oxide linkage between two monosaccharide units is called glycosidic linkage.
In disaccharides, if the reducing groups of monosaccharides i.e., aldehydic or ketonic groups are bonded,
these are non-reducing sugars, e.g., sucrose. On the other hand, sugars in which these functional groups are
free, are called reducing sugars, for example, maltose and lactose.
(i) Sucrose:
One of the common disaccharides is sucrose which on hydrolysis gives equimolar mixture of D-(+)-glucose and
D-(-) fructose.
𝐻+(𝑜𝑟)
C12H22O11 + H2O > C6H12O6 + C6H12O6
𝐼𝑛𝑣𝑒𝑟𝑡𝑎𝑠𝑒
Sucrose Glucose Fructose
These two monosaccharides are held together by a glycosidic linkage between C 1 of α-D-glucose and C2 of
β-D-fructose. Since the reducing groups of glucose and fructose are involved in glycosidic bond formation,
sucrose is a non reducing sugar.
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133
Sucrose is dextrorotatory but after hydrolysis gives dextrorotatory glucose and laevorotatory fructose. Since
the laevorotation of fructose (–92.4°) is more than dextrorotation of glucose (+ 52.5°), the mixture is
laevorotatory. Thus, hydrolysis of sucrose brings about a change in the sign of rotation, from dextro (+) to
laevo (–) and the product is named as invert sugar.
(ii) Maltose:
Maltose is composed of two α-D-glucose units in which C1 of one glucose (I) is linked to C4 of another glucose
unit (II). The free aldehyde group can be produced at C 1 of second glucose in solution and it shows reducing
properties so it is a reducing sugar.

(iii) Lactose:
Lactose is also calles as milk sugar (found in milk). It is composed of β-D-galactose and β-D-glucose. The
glycosidc linkage is between C1 of galactose and C4 of glucose. Free aldehyde group may be produced at C-1 of
glucose unit, hence it is also a reducing sugar.

Polysaccharides:
Polysaccharides contain a large number of monosaccharide units joined together by glycosidic linkages. These
are the most commonly encountered carbohydrates in nature. They mainly act as the food storage or
structural materials.
(i) Starch:
Starch is the main storage polysaccharide of plants. It is the most important dietary source for human beings.
High content of starch is found in cereals, roots, tubers and some vegetables. It is a polymer of α-glucose.
It consists of two components— Amylose and Amylopectin.
is and constitutes about. It is a in which chain is formed by
Amylose Amylopectin
It is water soluble insoluble in water
15-20% of starch contains amylose 80- 85% of starch contains amylo pectin
It is unbranched chain with 200-1000 α -D- It is branched chain polymer of α -D-glucose
(+)-glucose units units
It has C1– C4 glycosidic linkage. It has C1–C4 glycosidic linkage whereas
branching occurs by C1–C6 glycosidic linkage.
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133
(ii) Cellulose:
Cellulose occurs exclusively in plants and it is the most abundant organic substance in plant kingdom. It is a
predominant constituent of cell wall of plant cells. Cellulose is a straight chain polysaccharide composed only
of b-D-glucose units which are joined by glycosidic linkage between C 1 of one glucose unit and C4 of the next
glucose unit.

(iii) Glycogen:
The carbohydrates are stored in animal body as glycogen. It is also known as animal starch because its
structure is similar to amylopectin and is rather more highly branched. It is present in liver, muscles and brain.
When the body needs glucose, enzymes break the glycogen down to glucose. Glycogen is also found in yeast
and fungi.
Importance of Carbohydrates:
Carbohydrates are major portion of our food. Honey has been used for a long time as an instant source of
energy by ‘Vaids’ in ayurvedic system of medicine. Carbohydrates are used as storage molecules as starch in
plants and glycogen in animals. Cell wall of bacteria and plants is made up of cellulose. We build furniture,
etc. from cellulose in the form of wood and clothe ourselves with cellulose in the form of cotton fibre. They
provide raw materials for many important industries like textiles, paper, lacquers and breweries.
Two aldopentoses viz. D-ribose and 2-deoxy-D-ribose are present in nucleic acids.
Proteins:
Proteins are the most abundant biomolecules of the living system. Chief sources of proteins are milk, cheese,
pulses, peanuts, fish, meat, etc. They occur in every part of the body and form the fundamental basis of
structure and functions of life. They are also required for growth and maintenance of body. The word protein
is derived from Greek word, “proteios” which means primary or of prime importance. All proteins are
polymers of a-amino acids.
Amino acids:
Amino acids contain amino (–NH2) and carboxyl (–COOH) functional groups. Depending upon the relative
position of amino group with respect to carboxyl group, the amino acids can be classified as α, β, γ, δ and so
on. Only α-amino acids are obtained on hydrolysis of proteins. They may contain other functional groups also.
All α-amino acids have trivial names, which usually reflect the property of that compound or its source.
Glycine is so named since it has sweet taste (in Greek glykos means sweet) and tyrosine was first obtained
from cheese (in Greek, tyros means cheese.)
Amino acids are generally represented by a three letter symbol, sometimes one letter symbol is also used.

Classification of Amino Acids:

Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and
carboxyl groups in their molecule.
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133
Neutral amino acids: Amino acids contains equal number of amino and carboxyl groups are called neutral
amio acids. Ex: Glycine, Alanine, Valine, Leucine, isoleucine etc
Acidic amino acids: Amino acids contains more number of carboxyl groups are called Acidic amino acids.
Ex: Glutamic acid, Aspartic acid etc
Basic amino acids: Amino acids contains more number of amino groups are called Basic amino acids.
Ex: lysine, tryptophan, histidine, proline
Amino acids which contains Sulpher is Cysteine.
The amino acids, which can be synthesised in the body, are known as nonessential amino acids.
Ex: Glycine, Alanine, Glutamic acid, Aspartic acid, Cysteine, proline etc
The amino acids, which can not be synthesised in the body, are known as essential amino acids must be
obtained through diet, are known as essential amino acids.
Ex: Valine, Leucine, isoleucine, lysine, tryptophan, histidine etc
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133
Properties of amino acids:
Amino acids are usually colourless, crystalline solids. These are water-soluble, high melting solids and behave
like salts rather than simple amines or carboxylic acids. This behaviour is due to the presence of both acidic
(carboxyl group) and basic (amino group) groups in the same molecule.
In aqueous solution, the carboxyl group can lose a proton and amino group can accept a proton, giving rise to
a dipolar ion known as zwitter ion. This is neutral but contains both positive and negative charges.
In zwitter ionic form, amino acids show amphoteric behaviour as they react both with acids and bases.
Glycine is optically inactive. Except glycine all naturally occurring α-amino acids are optically active, since the
α-carbon atom is asymmetric. These exist both in ‘D’ and ‘L’ forms. Most naturally occurring amino acids have
L-configuration. L-Aminoacids are represented by writing the –NH2 group on left hand side.
Structure of Proteins:
Polymers are the derivatives of α-amino acids and they are connected to each other by peptide bond or
peptide linkage. Chemically, peptide linkage is an amide formed between –COOH group and –NH2 group.
Two amino acids combained form a product is called a dipeptide. It coatins one peptide linkage.
Three amino acids combained form a product is called a tripeptide. It coatins two peptide linkages.
Four amino acids combained form a product is called a tetrapeptide. It coatins three peptide linkages.
More no.of (n) amino acids combained form a product is called a Polypeptide. It coatins (n-1) no.of peptide
linkages.
Ex: Glycine combines with alanine form a dipeptide, glycylalanine it contains one peptide linkage.

A polypeptide with more than hundred amino acid residues, having molecular mass higher than 10,000u is
called a protein. However, the distinction between a polypeptide and a protein is not very sharp. Polypeptides
with fewer amino acids are likely to be called proteins if they ordinarily have a well defined conformation of a
protein such as insulin which contains 51 amino acids.
Proteins can be classified into two types on the basis of their molecular shape.
(a) Fibrous proteins:
When the polypeptide chains run parallel and are held together by hydrogen and disulphide bonds, then
fibre– like structure is formed. Such proteins are generally insoluble in water.
Ex: Keratin (present in hair, wool, silk) and myosin (present in muscles), etc.
(b) Globular proteins:
This structure results when the chains of polypeptides coil around to give a spherical shape. These are usually
soluble in water.
Ex: Insulin and albumins etc
Structure and shape of proteins can be studied at four different levels, i.e., primary, secondary, tertiary and
quaternary, each level being more complex than the previous one.
(i) Primary structure of proteins:
Proteins may have one or more polypeptide chains. Each polypeptide in a protein has amino acids linked with
each other in a specific sequence and it is this sequence of amino acids that is said to be the primary
structure of that protein. Any change in this primary structure i.e., the sequence of amino acids creates a
different protein.
(ii) Secondary structure of proteins:
The secondary structure of protein refers to the shape in which a long polypeptide chain can exist. They are
found to exist in two different types of structures viz. α-helix and β-pleated sheet structure. These structures
arise due to the regular folding of the backbone of the polypeptide chain due to hydrogen bonding between
and –NH– groups of the peptide bond.
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133
In α-Helix polypeptide chain forms all possible hydrogen bonds by twisting into a right handed screw (helix)
with the –NH group of each amino acid residue hydrogen bonded to the C=O of an adjacent turn of the helix.
In β-pleated sheet structure all peptide chains are stretched out to nearly maximum extension and then laid
side by side which are held together by intermolecular hydrogen bonds. The structure resembles the pleated
folds of drapery and therefore is known as β-pleated sheet.

(iii) Tertiary structure of proteins:

The tertiary structure of proteins represents overall folding of the polypeptide chains i.e., further folding of
the secondary structure. It gives rise to two major molecular shapes viz. fibrous and globular. The main forces
which stabilise the 2° and 3° structures of proteins are hydrogen bonds, disulphide linkages, van der Waals
and electrostatic forces of attraction.
(iv) Quaternary structure of proteins:
Some of the proteins are composed of two or more polypeptide chains referred to as sub-units. The spatial
arrangement of these subunits with respect to each other is known as quaternary structure.

Denaturation of Proteins:
Protein found in a biological system with a unique three-dimensional structure and biological activity is
called a native protein. Due to change in temperature or chemical change like change in pH, the hydrogen
bonds are disturbed then globules unfold and helix get uncoiled and protein loses its biological activity. This
is called denaturation of protein. During denaturation secondary and tertiary structures are destroyed but
primary structure remains intact.
Ex: The coagulation of egg white, curdling of milk (it is caused due to the formation of lactic acid by the
bacteria present in milk).
Enzymes:
Digestion of food, absorption of appropriate molecules and ultimately production of energy all these reactions
occur in the body under very mild conditions. This occurs with the help of certain biocatalysts called enzymes.
Almost all the enzymes are globular proteins. Enzymes are very specific for a particular reaction and for a
particular substrate. They are generally named after the compound or class of compounds upon which they
work. For example, the enzyme that catalyses hydrolysis of maltose into glucose is named as maltase.
𝑀𝑎𝑙𝑡𝑎𝑠𝑒
(Maltose) C12H22O11 > 2 C6H12O6 (Glucose)
Sometimes enzymes are also named after the reaction, where they are used. For example, the enzymes which
catalyse the oxidation of one substrate with simultaneous reduction of another substrate are named as
oxidoreductase enzymes. The ending of the name of an enzyme is -ase.
Mechanism of Enzyme Action:
Enzymes are needed only in small quantities for the progress of a reaction. Similar to the action of chemical
catalysts, enzymes are said to reduce the magnitude of activation energy. For example, activation energy for
acid hydrolysis of sucrose is 6.22 kJ mol–1, while the activation energy is only 2.15 kJ mol–1 when hydrolysed by
the enzyme, sucrase.
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133
Vitamins:
It has been observed that certain organic compounds are required in small amounts in our diet but their
deficiency causes specific diseases. These compounds are called vitamins. Most of the vitamins cannot be
synthesised in our body but plants can synthesise almost all of them, so they are considered as essential food
factors. However, the bacteria of the gut can produce some of the vitamins required by us. All the vitamins are
generally available in our diet.
Vitamins are designated by alphabets A, B, C, D, etc. Some of them are further named as sub-groups e.g. B1,
B2, B6, B12, etc. Excess of vitamins is also harmful and vitamin pills should not be taken without the advice of
doctor.
The term “Vitamine” was coined from the word vital + amine since the earlier identified compounds had
amino groups. Later work showed that most of them did not contain amino groups, so the letter ‘e’ was
dropped and the term vitamin is used these days.
Classification of Vitamins:
Vitamins are classified into two groups depending upon their solubility in water or fat.
(i) Fat soluble vitamins:
Vitamins which are soluble in fat and oils but insoluble in water are kept in this group. These are vitamins A, D,
E and K. They are stored in liver and adipose (fat storing) tissues.
(ii) Water soluble vitamins:
B group vitamins and vitamin C are soluble in water so they are called Water soluble vitamins. Water soluble
vitamins must be supplied regularly in diet because they are readily excreted in urine and cannot be stored
(except vitamin B12) in our body.
Vitamin Deficiency disease
Vit-A ( Retinol) Night blid ness, Xerophthalamia (hardening of cornea of eye)
Vit-B1 (Thiamine) Beri beri (loss of appetite, retarded growth)
Vit-B2 (Riboflavin) Cheilosis, Digestive disorders, Burning of sensation of skin
Vit- B3 (Niacin) Pellagra
Vit- B5 (Pantothenic acid) Burning feet
Vit- B6 (Pyridoxine) Convulsions
Vit- B7 (or) Vit-H (Biotin) Nerves disorders
Vit- B9 (Folic acid) Anaemia
Vit- B12 (Cyanocobalamine) Pernicious anaemia (RBC deficient in haemoglobin)
Vit- C (Ascorbic aid) Scurvy (bleeding gums)
Vit- D (Calciferol) Rickets (bone deformities in children) and osteomalacia (soft bones
and joint pain in adults)
Vit- E (Tocoferol) Increased fragility of RBCs and muscular weakness
Vit- K (Phylloquinone) Increased blood clotting time
Nucleic Acids:
The characteristics transmitted from one generation to the next generation is called heredity. The particles in
nucleus of the cell, responsible for heredity, are called chromosomes which are made up of proteins and
another type of biomolecules called nucleic acids. These are mainly of two types, the deoxyribonucleic acid
(DNA) and ribonucleic acid (RNA). Since nucleic acids are long chain polymers of nucleotides, so they are also
called polynucleotides.
Chemical Composition of Nucleic Acids:
Complete hydrolysis of DNA (or RNA) yields a pentose sugar, phosphoric acid and nitrogen containing
heterocyclic compounds (called bases).
Nucleic acid Pentose sugar Heterogeneous base
DNA β – D – 2 - deoxyribose Adenine, Guanine, Cytosine, Thymine.
RNA β – D – ribose Adenine, Guanine, Cytosine, Uracil.
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133

Structure of Nucleic Acids:

A unit formed by the attachment of a base to 1I position of sugar is known as nucleoside. In nucleosides, the
sugar carbons are numbered as 1I, 2I, 3I, etc. in order to distinguish these from the bases. When nucleoside is
linked to phosphoric acid at 5I -position of sugar moiety, we get a nucleotide.
Nucleotides are joined together by phosphodiester linkage between 5I and 3I carbon atoms of the pentose
sugar.
Pentose sugar + heterogeneous base → Nucleosides;
Nucleosides + Phosphate linkage → Nucleotides
Poly nucleotides are called nucleic acids.

The sequence of nucleotides in the chain of a nucleic acid is called its primary structure. Nucleic acids have a
secondary structure also.
James Watson and Francis Crick gave a double strand helix structure for DNA. Two nucleic acid chains are
wound about each other and held together by hydrogen bonds between pairs of bases. The two strands are
complementary to each other because the hydrogen bonds are formed between specific pairs of bases.
Adenine forms two hydrogen bonds with thymine whereas cytosine forms three hydrogen bonds with
guanine.

In secondary structure of RNA single stranded helics is present which sometimes foldsback on itself. RNA
molecules are of three types and they perform different functions. They are named as messenger RNA (m-
RNA), ribosomal RNA (r-RNA) and transfer RNA (t-RNA).
Biological Functions of Nucleic Acids:
DNA is the chemical basis of heredity and may be regarded as the reserve of genetic information. DNA is
exclusively responsible for maintaining the identity of different species of organisms over millions of years. A
DNA molecule is capable of self duplication during cell division and identical DNA strands are transferred to
daughter cells. Another important function of nucleic acids is the protein synthesis in the cell. Actually, the
proteins are synthesised by various RNA molecules in the cell but the message for the synthesis of a particular
protein is present in DNA.
CH.RAGHAVA RAO, S.D.C Pu college, Bangarpet,Kolar Ph:7411224133
Hormones:
Hormoes are inter cellular messengers produced by endocrine glands and poured into blood stream which
transports them to the site of action. Generally these are classified into three types. They are
Steroidal hormones: Estogens, Androgens
Poly peptide hormones: Insulin, Endophins
Amino acid derivatives: Epinephrine, norephinephrine, Thyroxine
The role of insulin in keeping the blood glucose level. Insulin is released in response to the rapid rise in blood
glucose level. On the other hand hormone glucagon tends to increase the glucose level in the blood.
The two hormones insulin and glucagon together regulate the glucose level in the blood.
Epinephrine and norepinephrine mediate responses to external stimuli.
Growth hormones and sex hormones play role in growth and development.
Thyroxine produced in the thyroid gland is an iodinated derivative of amino acid tyrosine. Abnormally low
level of thyroxine leads to hypothyroidism which is characterised by lethargyness and obesity and high level
of thyroxine causes hyperthyroidism. Low level of iodine in the diet may lead to hypothyroidism and
enlargement of the thyroid gland. This condition is largely being controlled by adding sodium iodide to
commercial table salt (“Iodised” salt).
Steroid hormones are produced by adrenal cortex and gonads (testes in males and ovaries in females).
Glucocorticoids control the carbohydrate metabolism, modulate inflammatory reactions, and are involved in
reactions to stress.
The mineralocorticoids control the level of excretion of water and salt by the kidney. If adrenal cortex does
not function properly then one of the results may be Addison’s disease characterised by hypoglycemia,
weakness and increased susceptibility to stress. The disease is fatal unless it is treated by glucocorticoids and
mineralocorticoids.
Hormones released by gonads are responsible for development of secondary sex characters. Testosterone is
the major sex hormone produced in males. It is responsible for development of secondary male characteristics
(deep voice, facial hair, general physical constitution) and estradiol is the main female sex hormone. It is
responsible for development of secondary female characteristics and participates in the control of menstrual
cycle. Progesterone is responsible for preparing the uterus for implantation of fertilised egg.

Intext Questions:
1. Glucose or sucrose are soluble in water but cyclohexane or benzene (simple six membered ring
compounds) are insoluble in water. Explain.
2. What are the expected products of hydrolysis of lactose?
3. How do you explain the absence of aldehyde group in the pentaacetate of D-glucose?
4. The melting points and solubility in water of amino acids are generally higher than that of the
corresponding halo acids. Explain.
5. Where does the water present in the egg go after boiling the egg?
6. Why cannot vitamin C be stored in our body?
7. What products would be formed when a nucleotide from DNA containing thymine is hydrolysed?
8. When RNA is hydrolysed, there is no relationship among the quantities of different bases obtained. What
does this fact suggest about the structure of RNA?

Exercises:
1. What are monosaccharides?
2. What are reducing sugars?
3. Write two main functions of carbohydrates in plants.
4. Classify the following into monosaccharides and disaccharides. Ribose, 2-deoxyribose, maltose, galactose,
fructose and lactose.
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5. What do you understand by the term glycosidic linkage?
6. What is glycogen? How is it different from starch?
7. What are the hydrolysis products of (i) sucrose and (ii) lactose?
8. What is the basic structural difference between starch and cellulose?
9. What happens when D-glucose is treated with the following reagents? (i) HI (ii) Bromine water (iii) HNO3
10. Enumerate the reactions of D-glucose which cannot be explained by its open chain structure.
11. What are essential and non-essential amino acids? Give two examples of each type.
12. Define the following as related to proteins (i) Peptide linkage (ii) Primary structure (iii) Denaturation.
13. What are the common types of secondary structure of proteins?
14. What type of bonding helps in stabilising the a-helix structure of proteins?
15. Differentiate between globular and fibrous proteins.
16. How do you explain the amphoteric behaviour of amino acids?
17. What are enzymes?
18. What is the effect of denaturation on the structure of proteins?
19. How are vitamins classified? Name the vitamin responsible for the coagulation of blood.
20. Why are vitamin A and vitamin C essential to us? Give their important sources.
21. What are nucleic acids? Mention their two important functions.
22. What is the difference between a nucleoside and a nucleotide?
23. The two strands in DNA are not identical but are complementary. Explain.
24. Write the important structural and functional differences between DNA and RNA.
25. What are the different types of RNA found in the cell?