Polysaccharides

• Starch


  • Mixture of two polymers, amylose (20%) and amylopectin (80%)
  • Amylose helices are trapped among amylopectin branches
  • Large and compact (stores lots of glucose)
  • Found in plant cells (energy store; starch grains in photosynthetic cells)
  • Can be hydrolysed to release glucose when needed
  • Insoluble in cell solution (no affect on water potential)
  • Osmotically inactive (no affect water diffusion)
• Amylose


  • Part of Starch
  • Long, straight, unbranched chains, each ~300 glucose units long
  • All bonds are α 1-4 glycosidic bonds
  • Chains curl into helices held by hydrogen bonds (between delta positive hydrogen of a hydroxyl group and delta negative oxygen of another)
  • Coils give a compact shape
• Amylopectin


  • Part of Starch
  • Branched, up to 1500 units of glucose
  • Joined by both α 1-4 and α 1-6 glycosidic bonds (1,6 bonds create branches every ~10 units)
  • Branches are more efficient as enzymes have more end points to break down from
  • Rapid hydrolysis by amylase (glucose collected quickly)
• Glycogen


  • Like amylopectin but shorter and more branched; more end points, quicker hydrolysis
  • Key in animals due to movement and temperature regulation
  • Has both α 1-4 and α 1-6 glycosidic bonds
  • Compact energy storage in non-photosynthetic cells
  • Found as small granules in animal cells' cytoplasm
  • Like starch, glycogen is insoluble and osmotically inactive
• Cellulose


  • Long, unbranched chains
  • Joined by β 1-4 glycosidic bonds
  • Alternate molecules are rotated 180° (prevent coiling)
  • Contains 10,000 β-glucose molecules
• Chitin


  • Large and structural
  • Forms storing fibres (e.g. for certain hard structures in invertebrates and fish)
  • Has acetamide group instead of hydroxyl group
  • Similar structure to Cellulose
• Callose


  • Linear homopolymer with repeating glucose units
  • Linked by 1-3 glycosidic bonds
  • Structural component in many pollen development stages