06/10/2025
LECTURE 7: PROTEINS — THE BUILDING BLOCKS OF LIFE
1. Introduction
Proteins are large, complex organic molecules made up of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sometimes sulphur (S) and phosphorus (P).
They are the body’s builders — responsible for growth, repair, and maintenance of tissues.
In short:
If carbohydrates give you energy, and lipids store it — proteins build you!
2. Composition of Proteins
Proteins are made up of smaller units called amino acids.
There are about 20 naturally occurring amino acids, and they link together through peptide bonds to form long chains.
Peptide bond:
Formed between the –COOH (carboxyl) group of one amino acid and the –NH₂ (amino) group of another, releasing a molecule of water (H₂O).
3. Classification of Proteins
(a) Simple Proteins
These yield only amino acids on hydrolysis.
Examples: Albumin (egg white), Globulin (blood plasma)
(b) Conjugated Proteins
Contain a non-protein part (called a prosthetic group).
Examples: Haemoglobin (iron-containing group), Glycoproteins
(c) Derived Proteins
Formed by the breakdown of simple and conjugated proteins.
Examples: Peptones, Proteoses
4. Levels of Protein Structure
1. Primary structure → Linear sequence of amino acids.
2. Secondary structure → Coiling or folding (e.g., alpha-helix, beta-sheet).
3. Tertiary structure → 3D arrangement of the chain.
4. Quaternary structure → Combination of multiple polypeptide chains (e.g., haemoglobin).
5. Functions of Proteins
Structural: Collagen (skin), Keratin (hair, nails).
Enzymatic: Enzymes speed up biochemical reactions.
Transport: Haemoglobin carries oxygen.
Hormonal: Insulin controls blood sugar.
Defensive: Antibodies fight infections.
Repair and Growth: Essential for tissue repair and muscle building.
6. Quick Recap
Proteins are made of amino acids joined by peptide bonds.
They have complex structures and perform diverse biological roles.
They’re essential for life — no protein, no you!
Quick Test
Which of the following elements is always present in proteins but not in carbohydrates or lipids?
A. Oxygen
B. Hydrogen
C. Nitrogen
D. Carbon
