Lecture on Polysaccharides

Introduction

• Definition: Polysaccharides are large carbohydrates consisting of many monosaccharides connected by O-glycosidic bonds.
• Purpose: Used for energy storage or providing structure in organisms.
  • Energy Storage: e.g., Glycogen in animals, Starch in plants.
  • Structural Support: e.g., Cellulose in plants.

Types of Polysaccharides

1. Glycogen

• Role: Major energy storage polysaccharide in animal cells.
• Structure:
  • Homopolymer of glucose molecules.
  • Bonds:
    • Alpha-1,4-glycosidic bonds create a helical structure.
    • Alpha-1,6-glycosidic bonds create branching points every 10 units.
• Function: Easily broken down into glucose for ATP production via glycolysis and the Krebs cycle.

2. Starch

• Role: Major energy storage polysaccharide in plants.

• Forms:

  • Amylose:
    • Unbranched with alpha-1,4-glycosidic bonds.
    • Helical structure due to these bonds.
  • Amylopectin:
    • Branched like glycogen but less frequent (every 30 units).
    • Contains both alpha-1,4 and alpha-1,6-glycosidic bonds.

• Digestion:

  • Broken down by alpha-amylase in saliva and pancreas.
  • Converts starches into maltose, further broken down by maltase in the intestine.

3. Cellulose

• Role: Provides structural support in plants.
• Structure:
  • Linear chains due to beta-1,4-glycosidic bonds.
  • Forms strong, stacked fibers with hydrogen bonding.
• Importance:
  • High tensile strength useful for plant cell structure.
  • Forms dietary fiber in human diet aiding digestion.

Summary

• Energy Storage: Glycogen and starch store energy and are converted to ATP.
• Structural Role: Cellulose provides structure, but humans cannot digest it.
• Dietary Fiber: Cellulose aids digestion and reduces toxin absorption.

This lecture covered the functions and structures of key polysaccharides, emphasizing their role in energy storage and structural support in various organisms.