Starch, glycogen and cellulose

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  • Created by: Laura
  • Created on: 27-04-14 09:45
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  • Starch, glycogen and cellulose
    • Starch
      • Starch is a poly-saccharide that is found in many parts of a plant
      • Large amounts occur in seeds and storage organs
      • Forms an important component of food and is the main energy source in most diets
      • Made up of chains of alpha glucose linked by glycosidic bonds that are formed by condensation reactions
      • Chain wound into a coil that makes the molecule very compact
      • Main role of starch is an energy source which it is suited for
        • It is insoluble - does not draw water into cell or diffuse out of cell
        • It is compact so a lot can be stored in a small place
        • Made of alpha glucose that is easily transported as well as readily used in respiration
    • Glycogen
      • Shorter chains and is highly branched
      • Storage in animals not plants
      • Stored mainly in the muscles and the liver cells
      • Smaller chains means it is even more readily hydrolysed to alpha glucose
    • Cellulose
      • Made of beta glucose not alpha glucose
      • H and OH group are reversed - each must be rotated 180 degrees to its neighbour to form glycosidic bonds
      • Straight, unbranched chains
      • These chains run parallel to each other allowing hydrogen bonds to form crosslinks between the chains
      • Very strong due to the vast number of hydrogen bonds
      • Cellulose molecules are grouped together to form micro-fibrils which are arranged in parallel groups called fibers
      • Major component of plant cell walls and provides rigidity to the plant cell
      • Also prevents plant cell from bursting as water enters by osmosis - exerts an inward pressure which stops any further influx of water


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