Polysaccharides

• What are Polysaccharides made from?

  Formed when more than two monosaccharides are joined together by condensation reactions.
• How do you break down Polysaccharides?

  Can be broken down into their constituent monosaccharides by hydrolysis reactions
• What are the 3 main Polysaccharides?

  Starch, glycogen, cellulose
• Function of starch

  • Cells get energy from glucose - plants store excess glucose as starch
  • When a plant needs more glucose for energy, it breaks down starch to release the glucose.
• What is starch a mixture of?

  Alpha glucose amylose and amylopectin
• Structure of Amylose

  • Long unbranched chain of alpha glucose
  • Angles of glycosidic bonds give it a coiled structure
  • Cylindrical structure makes it more compact so its really good for storage because more can fit in
• Structure of Amylopectin

  • Long, branched chain of alpha glucose
  • Side branches allow enzymes that break down the molecule to get at the glycosidic bonds easily. This means glucose can be released quickly.
• Why is starch good for storage?

  Insoluble in water and doesn't affect water potential, so doesn't cause water to enter cells by osmosis, which would make them swell.
• How do animals store extra glucose?

  Glycogen
• Structure of Glycogen

  Similar to amylopectin, except has more side branches coming of it. More branches mean that stored glucose can be released quickly which is important for energy release in animals. Is also a compact molecule, so good for storage.
• Structure of cellulose

  • Long, unbranched chains of beta-glucose molecules bond, they form straight cellulose chains.
  • Cellulose chains are linked together by hydrogen bonds to form strong fibres called microfibrils.
  • Strong fibres mean cellulose provides structural support for cells.
• What is the test for Starch?

  The Iodine test for starch
• What colour does iodine test change to to if there's starch present?

  Sample changes from browny-orange to a dark, blue-black colour.