Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen — usually in the ratio Cₙ(H₂O)ₙ. They are a primary source of energy for living organisms and play important structural and functional roles in cells.
Carbohydrates are broadly classified into three main types based on their structure and complexity:
1. Monosaccharides (Simple Sugars)
These are the simplest form of carbohydrates that cannot be broken down into smaller sugars by hydrolysis.
They are the building blocks of other carbohydrates.
Examples: Glucose, Fructose, Galactose
Key points:
- Contain 3–7 carbon atoms.
- Sweet in taste and soluble in water.
- Provide quick energy.
Types (based on carbon atoms):
- Triose (3 C): Glyceraldehyde
- Tetrose (4 C): Erythrose
- Pentose (5 C): Ribose (in RNA), Deoxyribose (in DNA)
- Hexose (6 C): Glucose, Fructose, Galactose
2. Disaccharides (Double Sugars)
Formed when two monosaccharides join together by a glycosidic bond, with the release of a water molecule (condensation reaction).
Examples:
- Sucrose = Glucose + Fructose (common table sugar)
- Lactose = Glucose + Galactose (milk sugar)
- Maltose = Glucose + Glucose (malt sugar)
Key points:
- Soluble in water and sweet in taste.
- Provide energy after digestion into monosaccharides.
3. Polysaccharides (Complex Carbohydrates)
These are large molecules made by joining many monosaccharides together through glycosidic bonds.
Examples:
- Starch – Storage form of glucose in plants.
- Glycogen – Storage form of glucose in animals (mainly in liver and muscles).
- Cellulose – Structural component of plant cell walls.
- Chitin – Found in the exoskeleton of insects and crustaceans.
Key points:
- Usually insoluble in water.
- Not sweet in taste.
- Serve as energy storage (starch, glycogen) or structural material (cellulose, chitin).