CBSE Class 12th Chemistry Notes: Biomolecules (Part - III)

This article provides you the revision notes on Class 12 Chemistry: Chapter - Biomolecules, to give you a quick glance of the chapter. In this part you will get to know about the Enzymes, Nucleic Acids and Vitamins, their various types and structures. These quick notes are prepared strictly according to the latest CBSE syllabus for Class 12th .Chemistry

Created On: Nov 8, 2016 16:50 IST
Modified On: Nov 9, 2016 16:15 IST

This article provides you the revision notes on Class 12 Chemistry: Chapter- Biomolecules, to give you a quick glance of the chapter. This article is a continuation of the revision notes on Class 12 Chemistry, Chapter- Biomolecules, Part-I & Part II. In Part-I & II you got acquainted to the Carbohydrates, Proteins, Amino acids and Peptides along with their various types. This Class 12 Chemistry: Chapter- Biomolecules, Part-III, explains you about the Enzymes, Nucleic Acids and Vitamins, their various types and structures. These quick notes are prepared strictly according to the latest CBSE syllabus for Class 12th Chemistry.

The main topics covered in this part are:

•    Enzymes

     o    Nomenclature of Enzymes

     o    Mechanism of Enzyme Action

•    Nucleic Acids

     o    Structure of Nucleic Acid

     o    Types of Nucleic Acid

     o    Structure of DNA

     o    Structure of RNA

     o    Importance of DNA

•    Vitamins

     o    Introduction

     o    Classification

•    Some important Vitamins

     o    Sources

     o    Deficiency Diseases

The key notes of the chapter are as follows:


•     Enzymes are proteinaceous substances which are used as biological catalysts.

•     Almost all the enzymes are globular proteins.

•     Being proteins, they have colloidal nature and get inactivated during reactions and have to be constantly replaced by synthesis in the body.

•     Enzymes are needed only in small quantities for the progress of a reaction.

•     Enzymes are very selective and specific for a particular reaction.

•     Enzymes lower the energy barrier that reactants must pass over to form the products.

•      An enzyme molecule may contain a nonprotein part which is known as prosthetic group.

It is of two types:

      o     Cofactor: The prosthetic group which is covalently attached with the enzyme molecule is known as cofactor.

      o     Coenzyme: The prosthetic group which get attached to the enzyme at the time of a reaction is known as coenzyme.

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Nomenclature of Enzymes

Enzymes are usually named by adding the suffix ‘ase’ to the root name of the substrate, e.g., urease, maltase, invertase, etc.

Mechanism of Enzyme Action

•   There is a lock and key arrangement between the an enzyme and a substrate.

•   Substrates bind at active site, temporarily forming an enzyme-substrate (E-S) complex.

•   The E-S complex undergoes internal rearrangements that form the product.

•   The enzyme gets regenerated for the next molecule of the substrate.

Nucleic Acids

Nucleic acids are chain like polymers of thousands of nucleotide units, hence they are also called polynucleotides.


A unit formed by the attachment of a base to 1′ position of sugar is known as nucleoside.


A nucleotide consists of three subunits: a nitrogen containing heterocyclic aromatic compound which is called base, a pentose sugar and a molecule of phosphoric acid.

Structure of Nucleic Acid

Thus a nucleic acid chain is represented as shown below.

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Types of Nucleic Acids

The nucleic acids are of two types:

(i) Deoxyribonucleic acid (DNA)

(ii) Ribonucleic acid (RNA)

•   DNA is mainly localised in the nucleus, within the chromosome. While small amount is present in cytoplasm. RNA is also present in the nucleus as well as cytoplasm.

•   DNA is mainly used in protein synthesis involving RNA and also a major source of genetic information.

•   DNA contains doxyribosee while RNA contains ribose.

Structure of DNA

•   DNA has a double helix structure in which the two strands are antiparellel and are held together by hydrogen bonds.

•   In DNA molecule, adenine (A) pairs up with thymine (T) via two hydrogen bonds and guanine (G) pairs up with cytosine (C) via three hydrogen bonds. Therefore CG base pair has more stability than AT base pair.


Structure of RNA

It is usually a single strand of ribonucleotides and take up right handed helical conformation.


Structural difference between DNA and RNA

There are mainly two structural differences Between DNA and RNA

•   Sugar part: DNA contains deoxyribose while RNA contain riboses.

•   Base part: In DNA, four bases have been found. They are adenine (A), guanine (G), cytosine (C) and thymine (T). The first three of these bases are found in RNA but thymine (T) is replaced by uracil (U) in place of Thymine.

Importance of DNA

•   DNA is the store house of the hereditary information of the organism.

•   DNA is involed in protein synthesis.


•   Vitamins are a group of organic compounds which are essential for normal growth and nutrition and are required in very small amounts for maintaining optimum growth and a good health.

•   Their absence causes specific deficiency diseases.

•   Most of the vitamins cannot be synthesised in our body but plants can synthesise almost all of them.

•   Vitamin D is an exception because it can be made in the skin from exposure to sunlight.

Classification of Vitamins

On the basis of solubility in water, vitamins are classified into the following two types:

•   Fat soluble vitamins: Vitamins A, D, E and K are oil soluble.

•   Water soluble vitamins: The group includes Vitamins B and C. These are stored in much lesser amounts in the cells.

Note: Vitamin H (Biotin) is an exception, since it is neither soluble in water nor in fat.

Some important Vitamins, their Sources and their Deficiency Diseases are dictated in the table given below

Name of Vitamin

Important Sources

Deficiency Diseases

Vitamin A

Fish liver oil, Milk, butter, egg yolk, green and yellow vegetables.

Night blindness, Xerophthalmia (hardening of cornea of eye).

Vitamin B1

Yeast, milk, green vegetables, cereals, fruits, egg yolk.

Beriberi (loss of appetite, retarded growth)

Vitamin B2

Egg yolk, liver, milk, green leafy vegetables.

Cracked lips, sore tongue, digestive disorders and burning sensation of the skin.

Vitamin B6

Milk, egg yolk, cereals, yeast, legumes.

Nervous disturbances and convulsions.

Vitamin B12

Meat, fish, kidney, eggs.

Pernicious anaemia (RBC deficient in haemoglobin)

Vitamin C

Citrus fruits, amla and green leafy vegetables.

Scurvy (bleeding gums)

Vitamin D

Exposure to sunlight, fish and egg yolk

Rickets (bone deformities in children) and osteomalacia (soft bones and joint pain in adults)

Vitamin E

Milk, ghee, vegetable oils like wheat germ oil, sunflower oil, cotton seed oil.

Increased fragility of RBCs and muscular weakness

Vitamin H

Milk, yeast, liver, kidney.

Loss of hair, dermatitis.

Vitamin K

Green leafy vegetables, fish, meat, cereals.

Increased blood clotting time

CBSE Class 12th Chemistry Notes: Biomolecules (Part - I)

CBSE Class 12th Chemistry Notes: Biomolecules (Part - II)

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