Biomolecules 🧪 | Class 11 Handwritten Notes | NEET

Biomolecules 🧪 | Class 11 Handwritten Notes | NEET | NCERT

Introduction

All living organisms are made up of biomolecules: organic and inorganic compounds.
Biomolecules are essential for structure, function, and regulation of cells.
Major classes: Carbohydrates, Proteins, Lipids, Nucleic Acids, Enzymes.

Carbohydrates

Composed of C, H, O (general formula Cn(H2O)n).
Functions: primary energy source, structural component, storage.

Types of Carbohydrates

1. Monosaccharides (simple sugars)

Smallest units, soluble.

Examples:

Glucose → main energy source.
Fructose → fruit sugar.
Galactose → in milk sugar.

2. Disaccharides (2 monosaccharides joined by glycosidic bond)

Maltose = Glucose + Glucose.
Sucrose = Glucose + Fructose.
Lactose = Glucose + Galactose.

3. Polysaccharides (long chains, storage/structural)

Starch → plant storage.
Glycogen → animal storage.
Cellulose → plant cell wall.
Chitin → exoskeleton of arthropods.

Biomolecules 🌝 - Biology Class 11th - Handwritten Notes

Proteins

Made of amino acids (20 types).

Bond: Peptide bond (C–N).

Structure:

Primary – sequence of amino acids.
Secondary – α-helix, β-pleated sheet (H-bonding).
Tertiary – 3D folding (ionic, hydrophobic, disulfide bonds).
Quaternary – multiple polypeptide chains (e.g., Hemoglobin).

Functions

Enzymes (biocatalysts).
Structural (collagen, keratin).
Hormones (insulin).
Transport (hemoglobin).
Defense (antibodies).

Lipids

Heterogeneous group, insoluble in water but soluble in organic solvents.
Functions: energy storage, insulation, membrane structure, hormones.

Types of Lipids

1. Simple lipids

Fats & oils (glycerol + fatty acids).
Saturated (no double bonds, solid at room temp).
Unsaturated (double bonds, liquid at room temp).

2. Compound lipids

Phospholipids → structural component of cell membrane (bilayer).
Glycolipids → lipid + carbohydrate.

3. Derived lipids

Steroids (cholesterol, testosterone, estrogen).
Waxes (protective coating on plants, skin).

Nucleic Acids

Genetic material of cells.
Composed of nucleotides (Nitrogenous base + Sugar + Phosphate).

Types

1. DNA (Deoxyribonucleic acid)

Double helix (Watson & Crick model, 1953).
Sugar = deoxyribose.
Bases: A–T, G–C (complementary base pairing).
Stores genetic information.

2. RNA (Ribonucleic acid)

Single-stranded.

Sugar = ribose.

Bases: A–U, G–C.

Types:

mRNA (messenger).
tRNA (transfer).
rRNA (ribosomal).

Functions in protein synthesis.

Enzymes

Biological catalysts → speed up chemical reactions without being consumed.
Mostly proteins (except ribozymes = RNA enzymes).
Highly specific in action.

Properties

Increase rate of reaction.
Work under mild conditions (pH, temperature).
Not consumed in reaction.
Sensitive to heat and pH.

Mechanism of Action

Lock and Key Model (Emil Fischer) → substrate fits exactly into active site.
Induced Fit Model (Koshland) → enzyme changes shape to fit substrate.

Factors Affecting Enzyme Activity

Temperature → optimum ~37°C in humans.
pH → optimum varies (pepsin = acidic, trypsin = alkaline).
Substrate concentration.
Inhibitors (competitive & non-competitive).

Cofactors

Non-protein components required by some enzymes.

Types:

Prosthetic groups (tightly bound).
Coenzymes (loosely bound, e.g., vitamins NAD⁺, FAD).
Metal ions (Mg²⁺, Zn²⁺).

Quick Table – Biomolecules

Biomolecule	Building Blocks	Key Functions	Example
Carbohydrates	Monosaccharides	Energy source, storage, structure	Glucose, Starch
Proteins	Amino acids	Enzymes, structure, transport, defense	Hemoglobin
Lipids	Glycerol + Fatty acids	Storage, membranes, hormones	Phospholipids
Nucleic Acids	Nucleotides	Genetic information, protein synthesis	DNA, RNA
Enzymes	Amino acids (proteins)	Catalysis of biochemical reactions	Amylase