Biomolecules 🌝 - Biology Class 11th - Handwritten Notes 📖 [PDF]📚

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.

Proteins

Made of amino acids (20 types).

Bond: Peptide bond (C–N).

Structure:

1. Primary – sequence of amino acids.
2. Secondary – α-helix, β-pleated sheet (H-bonding).
3. Tertiary – 3D folding (ionic, hydrophobic, disulfide bonds).
4. 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

1. Lock and Key Model (Emil Fischer) → substrate fits exactly into active site.
2. 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

Key Points for Exams

• Monosaccharide = basic unit of carbs.
• Protein structure levels (1° → 4°).
• Phospholipid bilayer = cell membrane.
• DNA = genetic storehouse; RNA = protein synthesis.
• Enzymes lower activation energy.
• Cofactors enhance enzyme action.