- The study of chemical changes within a living system is called biochemistry.

- Living systems are made up of complex biomolecules (carbohydrates, proteins, nucleic acids, lipids, etc.) and simple
molecules like vitamins and mineral salts.

CARBOHYDRATES (SACCHARIDES)
- They are optically active polyhydroxy aldehydes or ketones I. Glucose (Dextrose)
or the compounds which produce such units on hydrolysis. - It occurs freely in nature as well as in the combined form.
- They were considered as hydrates of carbon. - It is present in sweet fruits, honey, ripe grapes etc.
- General formula: Cx(H2O)y. E.g. molecular formula of - Monomer of larger carbohydrates like starch & cellulose.
glucose is C6H12O6, i.e., C6(H2O)6. - Probably the most abundant organic compound on earth.
- But all compounds with this formula are not carbohydrates. Preparation of Glucose
E.g. general formula of Acetic acid (CH3COOH) is 1. From sucrose (Cane sugar): Sucrose is boiled with dilute
C2(H2O)2 but is not a carbohydrate.
HCl or H2SO4 in alcoholic solution.
- There are carbohydrates without this general formula. E.g.
rhamnose (C6H12O5).
- The carbohydrates which are sweet in taste are called
2. From starch (commercial production): Hydrolysis of
sugars. E.g. sucrose, lactose (milk sugar).
starch by boiling with dil. H2SO4 at 393 K under pressure.
Classification of Carbohydrates
- Based on behaviour on hydrolysis, carbohydrates are 3 types:
monosaccharides, oligosaccharides & polysaccharides.
i. Monosaccharides Structure of glucose
- The carbohydrates that cannot be hydrolysed further to give Glucose is an aldohexose.
simpler unit of polyhydroxy aldehyde or ketone. Its structure is based on the following evidences:
- About 20 monosaccharides are known to occur in nature. 1. Its molecular formula is C6H12O6.
E.g. glucose, fructose, ribose, etc. 2. On prolonged heating with HI, it forms n-hexane. It proves
ii. Oligosaccharides that all 6 carbon atoms are linked in straight chain.

- They yield 2–10 monosaccharide units, on hydrolysis.

- They are classified as disaccharides, trisaccharides,
tetrasaccharides etc.
- Most common oligosaccharides are disaccharides. 3. Glucose reacts with hydroxylamine to form an oxime and
iii. Polysaccharides adds a hydrogen cyanide molecule to give cyanohydrin.
It confirms presence of carbonyl group (>C=O).
- They yield a large number of monosaccharide units on
hydrolysis. E.g. starch, cellulose, glycogen, gums etc.
- They are not sweet in taste; hence called non-sugars.
Reducing & non-reducing sugars:
- Reducing sugars: The carbohydrates which reduce 4. Glucose is oxidised to carboxylic acid (gluconic acid) on
Fehling’s solution & Tollens’ reagent. The reducing reaction with a mild oxidising agent like bromine water.
functional groups are aldehydic or ketonic groups. E.g. All It indicates that carbonyl group is present as an aldehyde.
monosaccharides (aldose & ketose), disaccharides with free
reducing groups. E.g. maltose & lactose. Gluconic
- Non-reducing sugars: The disaccharides having bonded acid
reducing groups of monosaccharides. E.g. Sucrose.
MONOSACCHARIDES 5. Acetylation of glucose with acetic anhydride gives
glucose pentaacetate. It confirms the presence of five –
- They are further classified on the basis of number of carbon
OH groups. Since it exists as a stable compound, five –OH
atoms and the functional group present in them.
groups should be attached to different carbon atoms.
- If a monosaccharide contains an aldehyde group, it is called
an aldose. If it has a keto group, it is called a ketose.
C atoms General term Aldehyde Ketone
3 Triose Aldotriose Ketotriose
4 Tetrose Aldotetrose Ketotetrose
5 Pentose Aldopentose Ketopentose 6. On oxidation with nitric acid, glucose & gluconic acid
6 Hexose Aldohexose Ketohexose yield a dicarboxylic acid (saccharic acid). It indicates the
7 Heptose Aldoheptose Ketoheptose presence of a primary alcoholic (–OH) group in glucose.
Page | 1 Anmol Sharma
 Glucose Saccharic acid Gluconic acid
- The exact spatial arrangement of different -OH groups was
given by Fischer.

- The two cyclic hemiacetal forms of glucose differ only in

the configuration of the hydroxyl group at C1, called
anomeric carbon (the aldehyde carbon before cyclisation).
Glucose Gluconic acid Saccharic acid Such isomers (a-form & b-form) are called anomers.
- Glucose is correctly named as D (+)-glucose. ‘D’ represents - The six membered cyclic structure of glucose is called
the configuration and ‘(+)’ represents dextrorotatory nature. pyranose structure (a– or b–), in analogy with pyran (a
- ‘D’ or ‘L’ before the name of a compound indicate relative cyclic compound with one oxygen atom & 5 carbon atoms).
configuration of a particular stereoisomer. This refers to - Cyclic structure of glucose is more correctly represented by
their relation with a particular isomer of glyceraldehyde. Haworth structure.
- Glyceraldehyde contains one asymmetric carbon atom and
exists in two enantiomeric forms as shown below.

II. Fructose
- The compound which is correlated to (+) glyceraldehyde is - A ketohexose sugar obtained by the hydrolysis of sucrose.
said to have D-configuration. Those which is correlated to - Molecular formula: C6H12O6.
(–) glyceraldehyde is said to have L– configuration. To Structure of Fructose
assign the configuration of monosaccharides, lowest
- It contains a ketonic functional group
asymmetric carbon atom is compared.
at carbon number 2.
- It belongs to D-series and is a
laevorotatory compound.
- It also exists in two cyclic forms
which are obtained by the addition of
–OH at C5 to the (>C=O) group.
- It is a five membered ring and is
named as furanose with analogy to the compound furan (a
Cyclic structure of glucose cyclic compound with one oxygen and 4 carbon atoms).
Open chain structure of glucose cannot explain the following:
1. Despite having the aldehyde group, glucose does not give
2, 4-DNP test, Schiff’s test and it does not form the
hydrogen sulphite addition product with NaHSO3.
2. Pentaacetate of glucose does not react with hydroxyl-
amine indicating the absence of free – CHO group.
3. Glucose exists in two different crystalline forms- a & b. - The cyclic structures of two anomers of fructose are
a-form (m.p. 419 K) is obtained by crystallisation from represented by Haworth structures as given.
concentrated glucose solution at 303 K. b-form (m.p. 423
K) is obtained by crystallisation from hot and saturated
aqueous solution at 371 K.
It was proposed that one–OH group may add to –CHO
group forming cyclic hemiacetal structure. Glucose forms
a six-membered ring in which –OH at C-5 is involved in
DISACCHARIDES
ring formation. This explains the absence of –CHO group
- Disaccharides on hydrolysis with dilute acids or enzymes
and existence of glucose in two forms. These two cyclic
forms exist in equilibrium with open chain structure. yield 2 molecules of the same or different monosaccharides.
- 2 monosaccharides are joined together by an oxide linkage

Page | 2 Anmol Sharma

 formed by the loss of a water molecule. Such a linkage (i) Starch
through oxygen atom is called glycosidic linkage. - Starch is the main storage polysaccharide of plants.
(i) Sucrose: - It is the most important dietary source for human beings.
- A disaccharide which on hydrolysis gives equimolar - Chief sources: Cereals, roots, tubers and some vegetables.
mixture of D- (+)-glucose and D- (-) fructose. - It is a polymer of a-glucose and consists of 2 components:
C12H22O11 + H2O → C6H12O6 + C6H12O6 Amylose & Amylopectin.
Sucrose D-(+)-glucose D-(-) fructose - Amylose: Water soluble component. It constitutes about 15-
20% of starch. It is a long unbranched chain with 200-1000
- These 2 monosaccharides are held together by a glycosidic
a-D-(+)-glucose units held by C1– C4 glycosidic linkage.
linkage between C1 of a-glucose and C2 of b-fructose.
- Since reducing groups of glucose & fructose are involved in
glycosidic bond, sucrose is a non-reducing sugar.

- Sucrose is dextrorotatory but after hydrolysis gives

dextrorotatory glucose and laevorotatory fructose.
- Since the laevorotation of fructose (–92.4°) is more than - Amylopectin: Insoluble in water. It constitutes about 80-
dextrorotation of glucose (+52.5°), the mixture is 85% of starch. It is a branched chain polymer of a-D-
laevorotatory. Thus, hydrolysis of sucrose brings about a glucose units in which chain is formed by C1–C4 glycosidic
change in the sign of rotation, from dextro (+) to laevo (–) linkage and branching occurs by C1–C6 glycosidic linkage.
and the product is named as invert sugar.
(ii) Maltose:
- It is composed of two a-D-glucose units in which C1 of one
glucose is linked to C4 of another glucose.
- The free aldehyde group can be produced at C1 of second
glucose in solution and it shows reducing properties. So it is
a reducing sugar.
(ii) Cellulose
- It occurs exclusively
in plants.
- It is the most abundant
organic substance in
plant kingdom.
- It is a constituent of
plant cell wall.
(iii) Lactose (Milk sugar): - It is a straight chain
- It is composed of b-D-galactose and b-D-glucose. polysaccharide
- The linkage is between C1 of galactose and C4 of glucose. composed only of b-
Hence it is also a reducing sugar. D- glucose units
joined by glycosidic linkage between C1 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, brain, yeast and fungi.
POLYSACCHARIDES - When the body needs glucose, enzymes break the glycogen
- They contain a large number of monosaccharide units down to glucose.
joined together by glycosidic linkages. Importance of Carbohydrates
- Most commonly encountered carbohydrates in nature. • Carbohydrates are primarily produced by plants. These are
- They mainly act as the food storage or structural materials. essential for life in both plants and animals.
Page | 3 Anmol Sharma
• Major portion of our food. Honey has been used for a long • Cellulose provide raw materials for many industries like
time as an instant source of energy by ‘Vaids’ in Ayurveda. textiles, paper, lacquers and breweries.
• Carbohydrates are used as storage molecules as starch in • 2 aldopentoses (D-ribose & 2-deoxy-D-ribose) are found in
plants and glycogen in animals. nucleic acids.
• Cell wall of bacteria and plants is made up of cellulose. • Carbohydrates are found in biosystem in combination with
• Cellulose (wood) is used to build furniture, etc. many proteins and lipids.
• Cellulose (cotton fibre) is used to make cloths.

PROTEINS
- Most abundant biomolecules in living system.
- Fundamental basis of structure and functions of life. 19. Histidine* His H
- They are required for growth & maintenance of body.
- Chief sources: milk, cheese, pulses, peanuts, fish, meat, etc.
- Proteins are polymers of a -amino acids. 20. Proline Pro P

AMINO ACIDS * Essential amino acids

- Amino acids contain amino (–NH2) & carboxyl (–COOH)
functional groups. Classification of Amino Acids
- Based on the relative position of amino - Based on relative number of amino and carboxyl groups,
group with respect to carboxyl group, amino acids are classified as follows:
amino acids are grouped as a, b, g, d etc. o Acidic: More carboxyl groups than amino groups.
- Only a-amino acids are obtained on o Basic: More amino groups than carboxyl groups.
o Neutral: Equal number of amino and carboxyl groups.
hydrolysis of proteins.
- Amino acids, which can be synthesised in the body, are
- All a-amino acids have trivial names, which usually reflect
known as non-essential amino acids.
the property of that compound or its source. E.g. Glycine
- Amino acids, which cannot be synthesised in body and must
has sweet taste (Greek glykos= sweet). Tyrosine was first
be obtained through diet, are called essential amino acids.
obtained from cheese (Greek, tyros = cheese).
- Amino acids are usually colourless, crystalline solids. These
20 Types of amino acids are water-soluble, high melting solids and behave like salts
3- letter 1 letter rather than simple amines or carboxylic acids. This
Amino acids Side chain, R
symbol code
1. Glycine H Gly G
behaviour is due to the presence of both acidic (carboxyl
2. Alanine – CH3 Ala A group) and basic (amino group) groups.
3. Valine* (H3C)2CH- Val V - In aqueous solution, the carboxyl group can lose a proton
4. Leucine* (H3C)2CH-CH2- Leu L and amino group can accept a proton, giving rise to a dipolar
H3C-CH2-CH- ion known as zwitter ion. This is neutral but contains +ve &
5. Isoleucine* | Ile I -ve charges. In zwitter ion, amino acids show amphoteric
CH3
behaviour as they react both with acids and bases.
HN=C-NH-(CH2)3-
6. Arginine* | Arg R
NH2
7. Lysine* H2N-(CH2)4- Lys K
8. Glutamic acid HOOC-CH2-CH2- Glu E - Except glycine, all other naturally occurring a-amino acids
9. Aspartic acid HOOC-CH2- Asp D are optically active, since the a -carbon atom is asymmetric.
O These exist both in ‘D’ and ‘L’ forms. Most naturally
10. Glutamine || Gln Q
H2N-C-CH2-CH2- occurring amino acids have L-configuration. L-Amino acids
O are represented by writing the –NH2 group on left hand side.
11. Asparagine || Asn N STRUCTURE OF PROTEINS
H2N-C-CH2-
- In a protein, a-amino acids are connected to each other by
12. Threonine* H3C-CHOH- Thr T
13. Serine HO-CH2- Ser S peptide bond (peptide linkage).
14. Cysteine HS-CH2- Cys C - Chemically, peptide linkage is an amide.
15. Methionine* H3C-S-CH2-CH2- Met M - Here, amino group (–NH2) of one molecule combines with
16. Phenylalanine* C6H5-CH2- Phe F carboxyl group (-COOH) of the other by the elimination of
17. Tyrosine (p)HO-C6H4-CH2- Tyr Y a water molecule. It forms a peptide bond –CO–NH–. The
product of the reaction is called a dipeptide.
18. Tryptophan* Trp W - E.g. when carboxyl group of glycine combines with the
amino group of alanine we get a dipeptide, glycylalanine.

Page | 4 Anmol Sharma

 >C=O of an adjacent turn of the helix.
- b-pleated sheet: In this, peptide chains are stretched out to
Glycylalanine nearly maximum extension and then laid side by side which
(Gly-Ala) are held together by intermolecular hydrogen bonds.
(iii) Tertiary structure:
- It represents overall folding of the polypeptide chains i.e.,
- If a third amino acid combines to a dipeptide, the product is
further folding of the secondary structure.
called a tripeptide.
- It gives rise to 2 major molecular shapes: fibrous & globular.
- When four, five or six amino acids are linked, they form
- The main forces which stabilize the 2° and 3° structures of
tetrapeptide, pentapeptide or hexapeptide respectively.
proteins are hydrogen bonds, disulphide linkages, Vander
- When the number of amino acids is more than ten, then the
Waals & electrostatic forces of attraction.
products are called polypeptides.
- A polypeptide with more than hundred amino acid residues, (iv) Quaternary structure:
having molecular mass higher than 10,000u is called a - Some proteins are made of two or more polypeptide chains
protein. However, the distinction between a polypeptide and (sub-units). The spatial arrangement of these subunits with
a protein is not very sharp. respect to each other is called quaternary structure.
- Polypeptides with fewer amino acids are likely to be called - Protein found in a biological system with a unique three-
proteins if they ordinarily have a well-defined conformation dimensional structure and biological activity is called a
of a protein. E.g. insulin (51 amino acids). native protein. If a native protein is subjected to physical
CLASSIFICATION OF PROTEINS change (e.g. temperature) or chemical change (e.g. pH), the
hydrogen bonds are disturbed. Due to this, globules unfold
Two types based on their molecular shape.
and helix get uncoiled and protein loses its biologic al
(a) Fibrous proteins activity. This is called denaturation.
- When polypeptide chains run parallel and are held together - Example of denaturation: Coagulation of egg white on
by hydrogen and disulphide bonds, it forms fibrous protein. boiling, curdling of milk due to the formation of lactic acid.
- They are generally insoluble in water. - During denaturation, 2° and 3° structures are destroyed but
- E.g. keratin (in hair, wool, silk) & myosin (in muscles) etc. 1º structure remains intact.
(b) Globular proteins ENZYMES
- When polypeptide chains coil around to give a spherical - Enzymes are biocatalysts.
shape, it forms globular protein. E.g. Insulin & albumins. - They are needed only in small quantities.
- These are usually soluble in water. - Almost all the enzymes are globular proteins.
Structural levels of proteins: 4 levels. - Enzymes are very specific for a particular reaction and for a
(i) Primary structure: particular substrate.
- The ending of the name of an enzyme is -ase.
- It is the sequence of amino acids in a polypeptide of a protein.
- Any change in primary structure creates a different protein. - They are named after the compound or class of compounds
upon which they work. E.g., the enzyme that catalyses
(ii) Secondary structure:
hydrolysis of maltose into glucose is named as maltase.
- It is the structures formed due to the regular folding of the - Enzymes are also named after the reaction. E.g., the
backbone of the polypeptide chain due to hydrogen bonding enzymes which catalyse oxido-reduction reactions are
between and –NH– groups of the peptide bond.
named as oxidoreductase.
- It is 2 types: a-helix and b-pleated sheet structure. - Like chemical catalysts, enzymes reduce the magnitude of
- a -Helix: Here, a polypeptide chain forms all possible H- activation energy. E.g. activation energy for acid hydrolysis
bonds by twisting into a right handed screw (helix) with the of sucrose is 6.22 kJ mol–1. It is reduced to 2.15 kJ mol–1 in
–NH group of each amino acid residue hydrogen bonded to presence of the enzyme, sucrose.

VITAMINS
- These are organic compounds required in the diet in small - Bacteria of the gut produce some vitamins.
amounts to perform specific biological functions for - Vitamins belong to various chemical classes.
maintenance of optimum growth & health of the organism. - Excess of vitamins is harmful. So vitamin pills should not
- The term “Vitamin” was coined from the word vital + be taken without the advice of doctor.
amine since the earlier identified vitamins had amino Classification of Vitamins
groups. But most of the vitamins have no amino groups. So, Based on their solubility in water or fat:
instead of vitamine, the term vitamin is used now. a. Fat soluble vitamins: Soluble in fat and oils but insoluble
- Our body cannot synthesize most of the vitamins. But plants in water. These are vitamins A, D, E and K. They are
can synthesize almost all vitamins. So they are considered stored in liver and adipose (fat storing) tissues.
as essential food factors.

Page | 5 Anmol Sharma

b. Water soluble vitamins: B group vitamins and vitamin C diet because they are readily excreted in urine and cannot
are soluble in water. They must be supplied regularly in be stored (except vitamin B12) in our body.
Vitamins Sources Deficiency diseases
Vitamin A Fish liver oil, carrots, butter & milk Xerophthalmia (hardening of cornea), Night blindness
Vitamin B1 Yeast, milk, green vegetables &
Beriberi (loss of appetite, retarded growth)
(Thiamine) cereals
Vitamin B2 Cheilosis (fissuring at corners of mouth and lips), digestive
Milk, egg white, liver, kidney
(Riboflavin) disorders and burning sensation of the skin.
Vitamin B6
Yeast, milk, egg yolk, cereals & grams Convulsions
(Pyridoxine)
Vitamin B12 Meat, fish, egg and curd Pernicious anaemia (RBC deficient in haemoglobin)
Vitamin C Citrus fruits, amla and green leafy
Scurvy (bleeding gums)
(Ascorbic acid) vegetables
Rickets (bone deformities in children) and osteomalacia (soft
Vitamin D Exposure to sunlight, fish & egg yolk
bones and joint pain in adults)
Vitamin E Vegetable oils like wheat germ oil, Increased fragility of RBCs and muscular weakness
sunflower oil etc.
Vitamin K Green leafy vegetables Increased blood clotting time

HORMONES
- These are molecules that act as intercellular messengers. • Steroid hormones from adrenal cortex:
- These are produced by endocrine glands. o Glucocorticoids: Control the carbohydrate metabolism,
- Chemically, they are steroids (e.g. estrogens & androgens), modulate inflammatory reactions, and are involved in
polypeptides (e.g. insulin & endorphins) or amino acid reactions to stress.
derivatives (e.g. epinephrine & norepinephrine). o Mineralocorticoids: Control the level of excretion of
- Hormones maintain the balance of biological activities. water and salt by the kidney.
Some hormones and their functions Improper functioning of adrenal cortex results in
• Glucagon & Insulin: They regulate blood glucose level.
Addison’s disease characterized by hypoglycemia,
weakness and increased susceptibility to stress. It should be
Glucagon increases glucose whereas Insulin decreases it.
treated by glucocorticoids & mineralocorticoids.
• Epinephrine & norepinephrine: They mediate responses
• Steroid hormones from gonads: Responsible for
to external stimuli.
development of secondary sex characters.
• Growth hormones & sex hormones: They play role in
growth and development. o Testosterone: Male sex hormone. It is responsible for
• Thyroxine: A thyroid hormone. It is an iodinated
development of secondary male characteristics (deep
voice, facial hair, general physical constitution).
derivative of amino acid tyrosine.
o Estradiol: Female sex hormone. It is responsible for
Low level of thyroxine leads to hypothyroidism. It is
development of secondary female characteristics and
characterized by lethargyness and obesity.
regulates menstrual cycle.
Increased level of thyroxine causes hyperthyroidism.
o Progesterone: Responsible for preparing the uterus for
Low level of iodine in the diet may lead to hypothyroidism implantation of fertilised egg.
and enlargement of the thyroid gland. This is controlled by
adding sodium iodide to table salt (“Iodised” salt).

NUCLEIC ACIDS
- These are the biomolecules present in chromosomes
(hereditary particles made up of proteins & nucleic acids).
- They are 2 types: Deoxyribonucleic acid (DNA) and
Ribonucleic acid (RNA).
- Nucleic acids are long chain polymers of nucleotides, so
they are also called polynucleotides.
Chemical Composition of Nucleic Acids - Nitrogen bases are N- containing heterocyclic compounds.
- Complete hydrolysis of DNA or RNA yields a pentose - 4 bases in DNA: Adenine (A), Guanine (G), Cytosine (C) &
sugar, phosphoric acid & nitrogen bases. Thymine (T).
- In DNA, the sugar is b-D-2-deoxyribose. In RNA, it is b - - 4 bases in RNA: Adenine (A), Guanine (G), Cytosine (C)
D-ribose. & Uracil (U).

Page | 6 Anmol Sharma

 - Information regarding sequence of nucleotides in a nucleic
acid chain is called its primary structure.
- James Watson & Francis Crick gave a
double strand helix structure (secondary
structure) for DNA.
- Two nucleic acid chains are coiled each
other and held together by hydrogen bonds
between pairs of bases.
- The two strands are complementary to each
other. Adenine pairs with thymine and
cytosine pairs with guanine.
Structure of Nucleic Acids - In secondary structure of RNA, single
- When a base is linked to 1′ position of sugar, it forms stranded helices are present. Sometimes
nucleoside. they fold back on themselves to form a
- When a nucleoside is linked to phosphoric acid at 5′- double helix structure.
position of sugar, it gives a nucleotide. - RNA are 3 types: messenger RNA (m-RNA), ribosomal
RNA (r-RNA) & transfer RNA (t-RNA).
DNA Fingerprinting
- A sequence of bases on DNA is unique for a person and
information regarding this is called DNA fingerprinting.
- It is same for every cell and cannot be altered.
Uses of DNA fingerprinting:
A nucleoside A nucleotide
• In forensic laboratories for identification of criminals.
- Nucleotides are joined together by phosphodiester linkage
• To determine paternity of an individual.
between 5′ and 3′ carbon atoms of the pentose sugar.
• To identify the dead bodies in any accident by comparing
the DNA’s of parents or children.
• To identify racial groups to rewrite biological evolution.
Biological Functions of Nucleic Acids:
• DNA is the chemical basis of heredity and the reserve of
genetic information.
• DNA maintains the identity of different species.
• DNA undergoes self-duplication during cell division and
identical DNA strands are transferred to daughter cells.
• Protein synthesis in the cell.
- Simplified version of nucleic acid chain:

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