Biological Molecules

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  1. How does the structure of polysaccharides help them to carry out their function?
    • Chains may be folded, making them compact and ideal for storage.
    • The size of the molecules make them insoluble, making them ideal for storage as they are osmotically inactive/do not affect water potential of the cell and do not easily diffuse out of the cell.
  2. Starch has monomers of ___________, and its function is to ___________ formed from any excess __________.
    alpha-glucose, reserve food, glucose
  3. Starch comprises of 20% amylose, 79% amylopectin & 1% phosphates and fatty acids.
    • Compact shape means many glucose residues can be stored in a small volume.
    • By converting small flucose molecules into a polysaccharide, small molecules are stored in large macromolecules.
    • Less water will enter by osmosis as the cell is less concentrated.
  4. Structure of Amylose
    • 300 alpha-glucose units, bonded by alpha-1,4 glycosidic linkages, making a 109 degree angle between 2 C-O bonds
    • causing the polymer to twist into a helix.
    • OH group of C2 projects out into the middle and form H bonds with each other, stabilising the shape.
  5. Structure of Amylopectin
    • Highly branched chains of 1300-1500 alpha-glucose subunits
    • alpha-1,4 glycosidic linkages give helical chains
    • alpha-1,6 glycosidic linkages give branch points
  6. In starch, amylopectin and amylose fit together to form a complex 3D structure in which amylose helices entangle in the branches of amylopectin molecules.
  7. Glycogen
    • comprises of alpha-glucose units with alpha-1,4 glycosidic linkages in helical chains and alpha-1,6 glycosidic linkages where branching occurs.
    • similar to amylopectin but has shorter chains and is more highly branched,
    • heavier, more compact and insoluble
  8. Cellulose
    • high Mr - 10000 beta-glucose monomers
    • glucose molecule rotated 180 degrees, upside down relative to adj molecule, giving a beta-1,4 glycosidic bond
    • successive molecules linked 180 degrees to each other by beta-1,4 glycosidic bonds
    • which are unreactive and can only by hydrolysed by cellulase.
    • (-OH) groups project from both sides of chain form H bonds with each other, forming cross-links
    • In a cell wall, 60-70 molecules become tightly cross-linked forming bundles of microfibrils which run roughly parallel to each other
    • Microfibrils are held together by H bonds to form fibres
    • Fibres embedded in gel-like organic matrix containing hemicelluloses and pectins, which help transfer the stress to fibres, increasing resistance to compression
  9. Where are starch, glycogen and cellulose found?
    • Starch granules in chlorophyll
    • Glycogen granules in cytoplasm of skeletal muscles and liver
    • Cell wall of plants

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Biological Molecules
2012-06-10 16:03:15

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