Carbohydrates

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  • Created by: farahh24
  • Created on: 11-09-18 13:36
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  • Carbohydrates
    • Glucose
      • Hexose monosaccharide - 6 carbons, 12 hydrogens, 6 oxygens
      • Structural variations
        • Alpha glucose has hydroxyl group below carbon 1
        • Beta glucose has hydroxyl group above carbon 1
      • Condensation reactions
        • Hydroxyl group on carbon-1 of first glucose molecule interacts with the hydroxyl group on carbon-4 of second glucose molecule.
          • Two hydroxyl groups form single oxygen with glycosidic bond. Water as waste product.
            • For beta glucose, the second glucose molecule must be turned upside down so hydroxyl groups are close enough to interact.
              • Beta glucose has hydroxyl group above carbon 1
    • Other sugars
      • Fructose + glucose = sucrose
      • Galactose + glucose = lactose
      • Ribose - pentose monosaccharide in RNA
      • Deoxyribose - pentose monosaccharide in DNA
    • Starch
      • Amylose
        • Alpha glucose molecules with 1-4 glycosidic bonds.
        • Twisted into helix - more compact, less soluble than glucose.
      • Amylopectin
        • Alpha glucose molecules with mostly 1-4 glycosidic bonds with some 1-6 glycosidic bonds.
        • 1-6 bonds form branches every ~25 subunits. Compact. Insoluble. Rigid.
      • Energy storage molecule for plants
    • Glycogen
      • More branches than amylopectin, more compact, requires less space to be stored.
        • Storage molecule for animals, which are more mobile than plants and require more carbohydrates
    • Cellulose
      • Beta glucose molecules (alternate molecules flipped upside down) forming 1-6 glycosidic bonds.
      • Straight, no branching or coils. Rigid. Not compact or soluble.
      • Make hydrogen bonds with each layer, forming microfibrils.
        • Microfibrils form macrofibrils, which form fibres.
    • Testing for carbohydrates
      • Benedicts test for reducing sugars
        • Add equal volume of Benedict's reagent. Heat mixture in water bath for five minutes.
      • Benedict's test for non-reducing sugars
        • Boiled with hydrochloric acid. Add equal volume of Benedict's reagent. Heat mixture in water bath for five minutes.
      • Iodine test
        • Add drops of iodine dissolved in potassium iodide solution.
          • If starch is present, solution will change from yellow/ brown to purple/ black
    • Reducing vs non-reducing sugars
      • Reducing: can act as reducing agent
        • Non-reducing: do not have hydroxyl group on anomeric carbon and cannot act as reducing agent.
          • Lactose is a reducing sugar. Sucrose in a non-reducing sugar.
  • No sugars present: blue. Increasing concentration of sugars present: green, yellow, orange, red.

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