Lecture Notes: Polysaccharides

Introduction to Polysaccharides

• Definitions:
  • Saccharides: Sugars
  • Monosaccharides: One sugar molecule (e.g., alpha glucose)
  • Disaccharides: Two sugar molecules linked (e.g., maltose)
  • Polysaccharides: Many repeating sugar units linked by glycosidic bonds
• Example:
  • Alpha Glucose: A monosaccharide
  • Formation of glycosidic bonds through condensation reactions

Formation of Polysaccharides

• Condensation Reaction:
  • Removal of water to link two monosaccharides
  • Forms disaccharides like maltose
• Polysaccharide Formation:
  • Repeated linking of monosaccharides
  • Poly is generally more than 20 sugar units

Starch: Polysaccharide in Plants

• Energy Storage Molecule
  • Stored in plant cells to prevent glucose diffusion
  • Insoluble in water, preventing osmotic pressures
• Types of Starch:
  • Amylose:
    • Made of alpha 1,4 glycosidic bonds
    • Helical or spiral shape
  • Amylopectin:
    • Made of alpha 1,4 and alpha 1,6 glycosidic bonds
    • Branched structure

Glycogen: Polysaccharide in Animals

• Energy Storage Molecule
  • Similar to amylopectin but more branched
  • Prevents osmotic pressure issues in animal cells

Cellulose: Structural Polysaccharide

• Made of Beta Glucose:
  • Beta 1,4 glycosidic bonds
  • Linear structure due to alternating glucose rotation
• Importance:
  • Forms plant cell walls
  • High tensile strength due to hydrogen bonds between chains
  • Microfibrils and fibers provide structural integrity

Comparison of Polysaccharides

1. Starch:
   • Function: Energy storage in plants
   • Structure: Helical (amylose) and branched (amylopectin)
2. Glycogen:
   • Function: Energy storage in animals
   • Structure: More branched than amylopectin
3. Cellulose:
   • Function: Structural component in plants
   • Structure: Linear due to beta 1,4 bonds

Summary

• Alpha vs. Beta Glucose:
  • Alpha glucose forms helical structures
  • Beta glucose forms linear structures due to alternating bonding
• Significance:
  • Polysaccharides prevent glucose diffusion and osmotic imbalance in cells
  • Structural polysaccharides like cellulose provide rigidity to plant cells

• Note: Understanding polysaccharides is crucial for recognizing how energy is stored and structural integrity is maintained in cells.