Biology Lecture: Polysaccharides

Introduction

• Final lesson in the carbohydrates series: Polysaccharides
• Created by condensation reactions bonding glucose monomers
• Three key polysaccharides:
  • Starch: found in plants, storage of glucose
  • Cellulose: found in plants, provides structural strength
  • Glycogen: found in animals, storage of glucose

Key Points for Polysaccharides

• Monomers: Glucose
• Bonds: Glycosidic bonds
• Function: Related to storage or structural support
• Location: Plants (starch and cellulose) and animals (glycogen)
• Importance of linking structure to function for higher understanding

Detailed Overview

Starch

• Polymers: Two types from alpha glucose - Amylose and Amylopectin
• Location: Plant cells, such as chloroplasts
• Function: Insoluble store of glucose

Amylose

• Formed by 1-4 glycosidic bonds
• Structure: Unbranched chain that coils into a helix

Amylopectin

• Formed by 1-4 and 1-6 glycosidic bonds
• Structure: Branched chain due to 1-6 bonds

Glycogen

• Monomer: Alpha glucose
• Location: Muscle and liver cells in animals
• Function: Insoluble store of glucose
• Structure: Highly branched with more 1-6 bonds than amylopectin

Cellulose

• Monomer: Beta glucose
• Location: Plant cell walls
• Function: Provides structural strength
• Structure: Long, straight chains of beta glucose, parallel alignment, held by hydrogen bonds forming fibrils
• Many hydrogen bonds collectively provide strength

Functional Analysis

• Starch and Glycogen:
  • Helix shape of amylose allows compact storage
  • Branching in amylopectin/glycogen increases accessibility for enzyme action
  • Insolubility prevents altering water potential and affecting osmosis
• Cellulose:
  • Structural strength due to extensive hydrogen bonds

Conclusion

• Importance of understanding structure-function relationship in polysaccharides
• Encouragement to review, practice questions, and test understanding of carbohydrates