B1.1.5

• Starch (in plants) and glycogen (in animals) are used as energy stores.
• Starch is a polymer of alpha glucose molecules with glycosidic bonds linking the molecules together. The chains coil up into a spring shape because of the shape of the monomer and the angle of the glycosidic bonds that join Carbon 1 of one monomer to Carbon 4 of the next, forming a 1-4 bond.
• There are two types of starch molecules.
• Amylose:

  • unbranded chain of alpha glucose
  • the bond angles make it helical (cylinder shape)
• Amylopectin:

  • same structure as amylose
  • some 1-6 bonds which makes the molecule branched.
  • the side branches makes it easy for the enzymes to get to the glycosidic bonds (glucose can be released quickly)
• Starch:

  • the major carbohydrate storage molecule in plants
  • stored as intracellular starch grains in plastids
  • produced from glucose during photosynthesis
  • can be broken down during respiration
• Glycogen contains alpha 1-6 glycosidic bonds that produce a branched structure.
• Glycogen:

  • the main energy storage in animals
  • animals store excess glucose as glycogen
  • the structure of glycogen is very similar to amylopectin (loads of branches)
  • a lot of branches means that glucose can be released quickly
  • glycogen is stored as small granules, f.e. in muscles and liver
  • glycogen is less dense and more soluble than starch