Maharashtra Board Class 12 Chemistry Chapter 14 Biomolecules PDF Download

14. Biomolecules

Can You Recall?

What are the constituents of balanced diet?

What are the products of digestion of carbohydrates?

Which constituent of diet is useful for building muscles?

Which constituent of diet is a source of high energy?

What is the genetic material of organisms?

14.1 Introduction: Principal Molecules Of The Living World

Bodies of living organisms contain large number of different molecules which constitute their structure. They are also part of various physiological processes taking place in them. Primary structural materials of organisms are proteins and cellulose. By means of the unique process of photosynthesis plants produce carbohydrates. Plants utilize the minerals absorbed by their roots to produce proteins. Lipids are the main ingredient of vegetable oils and milk fats. Nucleic acids constitute the genetic material of organisms.

In this chapter we are going to study some aspects of three principal biomolecules, namely, carbohydrates, proteins and nucleic acids.

14.2 Carbohydrates

From the simple chemical reactions of many carbohydrates it is understood that carbohydrates are polyhydroxy aldehydes or ketones or compounds which give rise to such units on hydrolysis. Some carbohydrates like glucose, fructose are sweet in taste, and are called sugars. The most commonly used sugar is sucrose which is obtained from sugarcane or sugar beet. The sugar present in milk is called lactose.

Try This

Observe the following structural formulae carefully and answer the questions.

CHO
(CHOH)4
CH2OH
(glucose)

CHO
(CHOH)3
CH2OH
(ribose)

CH2OH
(CHOH)3
CO
CH2
OH
(fructose)

1. How many OH groups are present in glucose, fructose and ribose respectively?

2. Which other functional groups are present in these three compounds?

Greek word for sugar is sakkharon. Hence carbohydrates are also called saccharides. Origin of the term carbohydrate lies in the finding that molecular formulae of many of them can be expressed as \(C_x(H_2O)_y\) (hydrates of carbon). For example: glucose \((C_6H_{12}O_6\) or \(C_6(H_2O)_6\), sucrose \((C_{12}H_{22}O_{11}\) or \(C_{12}(H_2O)_{11}\)), starch \([(C_6H_{10}O_5)_n\) or \([C_6(H_2O)_5]_n\).

14.2.1 Classification Of Carbohydrates

Carbohydrates are classified into three broad groups in accordance with their behaviour on hydrolysis. These are monosaccharides, oligosaccharides and polysaccharides.

Monosaccharides do not hydrolyse further into smaller units of polyhydroxy aldehydes or ketones. Oligosaccharides on hydrolysis yield two to ten units of monosaccharides and accordingly they are further classified as disaccharides, trisaccharides and so on. Polysaccharides give very large number of monosaccharide units on complete hydrolysis.

Teacher's Note

Carbohydrates are the main food in India. Rice and wheat give us carbohydrates which give us energy to work and play.

Exam Trick

Remember: Mono = one, Di = two, Poly = many. Monosaccharides have one sugar unit, disaccharides have two sugar units joined together.

Points to Remember

Carbohydrates are made of carbon, hydrogen and oxygen atoms.
Monosaccharides cannot be broken down into smaller sugar units.
Disaccharides are made of two monosaccharides joined together.
Polysaccharides are made of many monosaccharides joined together.
Glucose, fructose and sucrose are common carbohydrates in our food.

This is a preview of the first 3 pages. To get the complete book, click below.