Oligosaccharides and Polysaccharides

Oligosaccharides

Definition

• Oligosaccharides are carbohydrates made up of 2–10 monosaccharide units linked by glycosidic bonds.

• The most common oligosaccharides are disaccharides (two monosaccharides).

Types and Examples

Functions

• Provide quick energy when hydrolyzed.

• Serve as transport sugars in plants (sucrose).

• Act as precursors for polysaccharide synthesis.

🔹 Polysaccharides

Definition

• Polysaccharides are large, complex carbohydrates formed by polymerization of many monosaccharides.

• They are insoluble in water and serve storage or structural functions.

Types

1. Starch

• Storage polysaccharide in plants.

• Made of Amylose and Amylopectin.

  • Amylose: Linear chain of glucose units linked by α‑1,4 bonds.

  • Amylopectin: Branched chain with α‑1,4 and α‑1,6 bonds.

• Found in cereals, potatoes, and grains.

• Digested by amylase enzyme to maltose and glucose.

2. Cellulose

• Structural polysaccharide in plant cell walls.

• Linear chain of β‑D‑glucose units linked by β‑1,4 bonds.

• Insoluble and indigestible by humans.

• Provides rigidity and strength to plants.

3. Chitin

• Found in exoskeletons of insects, crustaceans, and fungi cell walls.

• Composed of N‑acetylglucosamine units linked by β‑1,4 bonds.

• Provides protection and structural support.

Functions of Polysaccharides

• Energy storage (starch, glycogen).

• Structural support (cellulose, chitin).

• Protective coatings (chitin in shells).

• Dietary fiber (cellulose aids digestion).

✅ Exam Summary

• Oligosaccharides → 2–10 monosaccharides (Sucrose, Lactose, Maltose).

• Polysaccharides → Many monosaccharides (Starch, Cellulose, Chitin).

• Key Bonds: α‑1,4, α‑1,6 (starch); β‑1,4 (cellulose, chitin).