A Level Biology – Biological Molecules
1. Biological Molecules Overview
Biological molecules are essential compounds that make up living organisms.
They include: Carbohydrates, Lipids, Proteins, Nucleic Acids (DNA & RNA), Water, Inorganic
Ions.
They are mostly organic compounds (contain carbon).
2. Carbohydrates
a. Monosaccharides: Single sugar units. General formula: (CH₂O)ₙ, e.g., glucose = C ₆H ₁₂O ₆.
Examples: Glucose (Alpha and Beta), Fructose, Galactose.
b. Disaccharides: Formed by condensation reactions (removal of water). Bond: Glycosidic
bond.
Examples: Maltose = glucose + glucose, Sucrose = glucose + fructose, Lactose = glucose +
galactose.
c. Polysaccharides: Large, insoluble molecules. Examples:
Starch (amylose & amylopectin, storage in plants), Glycogen (animal storage), Cellulose
(plant cell walls).
3. Lipids
a. Triglycerides: 1 glycerol + 3 fatty acids. Bond: Ester bond. Function: Energy storage,
insulation.
b. Fatty Acids: Saturated (no double bonds), Unsaturated (with double bonds).
c. Phospholipids: 1 glycerol + 2 fatty acids + phosphate. Forms bilayers due to hydrophilic
heads and hydrophobic tails.
4. Proteins
a. Structure: Monomers = amino acids (20 types). Contain NH ₂, COOH, and R group.
b. Peptide Bonds: Formed via condensation between amino and carboxyl groups.
c. Protein Structures:
1. Biological Molecules Overview
Biological molecules are essential compounds that make up living organisms.
They include: Carbohydrates, Lipids, Proteins, Nucleic Acids (DNA & RNA), Water, Inorganic
Ions.
They are mostly organic compounds (contain carbon).
2. Carbohydrates
a. Monosaccharides: Single sugar units. General formula: (CH₂O)ₙ, e.g., glucose = C ₆H ₁₂O ₆.
Examples: Glucose (Alpha and Beta), Fructose, Galactose.
b. Disaccharides: Formed by condensation reactions (removal of water). Bond: Glycosidic
bond.
Examples: Maltose = glucose + glucose, Sucrose = glucose + fructose, Lactose = glucose +
galactose.
c. Polysaccharides: Large, insoluble molecules. Examples:
Starch (amylose & amylopectin, storage in plants), Glycogen (animal storage), Cellulose
(plant cell walls).
3. Lipids
a. Triglycerides: 1 glycerol + 3 fatty acids. Bond: Ester bond. Function: Energy storage,
insulation.
b. Fatty Acids: Saturated (no double bonds), Unsaturated (with double bonds).
c. Phospholipids: 1 glycerol + 2 fatty acids + phosphate. Forms bilayers due to hydrophilic
heads and hydrophobic tails.
4. Proteins
a. Structure: Monomers = amino acids (20 types). Contain NH ₂, COOH, and R group.
b. Peptide Bonds: Formed via condensation between amino and carboxyl groups.
c. Protein Structures:
