Biomolecules

Notes

COMPLETE NOTES

BIOMOLECULES

Definition

Biomolecules are naturally occurring organic compounds present in living organisms.

Examples:

Carbohydrates

Proteins

Nucleic acids

Vitamins

1. CARBOHYDRATES

Definition

Carbohydrates are optically active polyhydroxy aldehydes or ketones or compounds that produce them on hydrolysis.

General Formula:

C

x

​

(H

2

​

O)

y

​

Classification

(A) Monosaccharides

Cannot be hydrolysed further.

Examples:

Glucose

Fructose

Ribose

Properties

Sweet

Water soluble

Reducing sugars

(B) Oligosaccharides

Contain 2–10 monosaccharide units.

Important Disaccharides

Sugar Constituent Sugars

Sucrose Glucose + Fructose

Maltose Glucose + Glucose

Lactose Glucose + Galactose

(C) Polysaccharides

Contain hundreds of glucose units.

Examples

Polysaccharide Function

Starch Storage food in plants

Glycogen Storage food in animals

Cellulose Cell wall of plants

Glucose

Molecular Formula

C₆H₁₂O₆

Important facts

Aldohexose

Exists in open chain and cyclic forms

Shows mutarotation

Forms pyranose ring

Why glucose does not give Schiff's test?

Because aldehyde group is involved in cyclic hemiacetal formation.

Why glucose reduces Tollens' reagent?

Because cyclic form opens into open-chain aldehyde form.

Fructose

Ketohexose

Exists mainly as furanose ring

Difference between Glucose and Fructose

Glucose Fructose

Aldose Ketose

Pyranose Furanose

Aldehyde group Ketone group

Reducing and Non-reducing Sugars

Reducing sugars

Glucose

Maltose

Lactose

Non-reducing sugar

Sucrose

2. PROTEINS

Definition

Proteins are polymers of α-amino acids linked by peptide bonds.

Amino Acid

General Formula

NH₂–CH(R)–COOH

Contains

Amino group

Carboxyl group

Peptide Bond

Bond formed between

COOH of one amino acid

NH₂ of another amino acid

Types of Proteins

Fibrous

Examples

Keratin

Silk

Characteristics

Insoluble

Structural role

Globular

Examples

Enzymes

Albumin

Characteristics

Water soluble

Functional role

Levels of Protein Structure

Primary → Amino acid sequence

Secondary → α-Helix and β-sheet

Tertiary → 3D folding

Quaternary → Association of subunits

Denaturation of Proteins

Loss of biological activity due to destruction of secondary and tertiary structures.

Causes

Heat

Acid

Base

Alcohol

Example

Boiling of egg.

3. ENZYMES

Definition

Biological catalysts made of proteins.

Characteristics

Highly specific

Work under mild conditions

Lower activation energy

…