AS OCR Biology: Reactions, Carbohydrates and Water

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  • Created on: 27-04-13 18:48
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  • Carbohydrates and Water
    • Chemical Reactions
      • Metabolism
        • Sum totall of all the biochemical reactions taking place in an organism. It involves both anabolic and catabolic reactions.
      • Anabolic Reactions
        • Involves building smaller molecules into larger ones and often involve condensation and is important in the formation of polymers
          • Condenationsis when two molecules are joined together when a covalent bond is formed by the elimination of a water molecule
      • Catabolic Reactions
        • Involves breaking down large molecules into smaller ones and often involves hydrolosis and is important in digestion of polymers into their constituent monomers
          • Hydrolysis is when a molecule is broken down when a covalent bond is broken by the addition of a water molecule
    • Carbohydrates
      • Main Functions are energy stores (glucose), energy store (starch in plants and glycogen in animals) and structural (cellulose)
      • 3 main types
        • Monosaccharides (single, simple sugars)
          • Contains C,H and O on the ratio of 1:2:1
          • All are sweet tasting, soluble in water and crystalline
          • Glucose is a hexose sugar.The two different forms of glucose are alpha and beta glucose. They both have the same molecular formula, but are arranged differently
            • 2 Alpha Glucose molecules join to make maltose (a disachharide)and hundreds of molecules join to form starch & glycogen (polysaccharides)
            • Hundreds of Beta Glucose molecules can be joined to make cellulose which is a polysaccharide.
        • Disaccharides(Molecules made by joining 2 single sugars together)
          • 2 a glucose molecules can be joined through condensationto make maltose, which is a double sugar.
          • During condensation, water is removed by losing the OH from c1 of one alpha glucose molecule and H from c4 of the second a glucose molecule.
        • Polysaccharides (Molecules made by joining many simple sugars together
          • Starch is an energy source in plants. It's a mixture of 2 polysaccharids (amylose and amylopectin. Amylose is a long chain of a-glucose joined by 1,4 glycosidic  bonds formed by condensation. It's formed in a helix
          • Glycogen is an energy store in animals, it's a polymer of a-glucose and formed by 1,4 glycosidic bonds formed by condensation. It's branched making it more compact, the branches are made by 1,6 glycosidic bonds
          • Cellulose is structural and found in plant cell walls. It's a polymer of B-Glucose joined by 1,4 Glycosidic bonds formed by condensation.Every second molecule is rotated 180 degrees. It makes them staight and unbranched.
            • This makes cellulose stright and unbranched and allows them to line up to make microfibrils containing ~70 cellulose molecules which are cross-linked by H bonds which are weak forces.
              • Microfibrils are held by H bond to form macrofibrils. Cellulose is insoluble and very strong.
      • Testing for sugars
        • All monosaccharides and many disaccharidesare reducing sugars. They can add electrons with other molecules (reduction)
        • When  a reducing sugar is heated, with Bendicts solution (CuS04 : Cu2+) the sugars reuces copper sultphate to form a brick red ppt of copper oxide.
        • To test for a non reducing sugar, do the Benedicts test, boil sample with HCl acid, cool sample, and neutralise HCl with Sodium hydrogen carbonate and do Benedicts again. Brick red PPT indicates that reducing sugars are present. Sucrose is an non reducing sugar.
        • A quantitative test tells you how much reducing sugar is present. To do it, make up standards and do the benedicts test on it. Filter off the ppts and measure % transmission. Plot a calibration curve. Do benedicts on samples, filter & measure & transmission and use CC convert % transmission.
    • Water
      • It's a polar molecule. The O atoms are slightly negatively charged and H atoms are slightly positvley charged.
      • Roles of water
        • Transport Medium. Good solvent due to polarity and allows water to flow as a body carrying dissolved substances with it
        • Ice & Insulation. H bonds in liquid always break and reform. In ice, they're fixed, so that the water molecules arrange in lacttice = more space, meaning ice less dense than water so it floats
        • Coheshion.H bonds "Sitck water molecules together, helping to draw water up the xylem and creating surface tension.
        • Environment. H bonds restrict the movemnt of water molecules so a large amount of energy is needed to increase the temp, meaning oceans have a fairly constant temperature.
        • Reactant. Used in hydrolysis reactions
        • H bonds in liquid water need to absorb a lot of heart energy before they break to make water vapour. Water has a high latent heat of evaporation and when it does, it draws heat energy from the surrounding, cooling surfaces
  • Carbohydrates
    • Main Functions are energy stores (glucose), energy store (starch in plants and glycogen in animals) and structural (cellulose)
    • 3 main types
      • Monosaccharides (single, simple sugars)
        • Contains C,H and O on the ratio of 1:2:1
        • All are sweet tasting, soluble in water and crystalline
        • Glucose is a hexose sugar.The two different forms of glucose are alpha and beta glucose. They both have the same molecular formula, but are arranged differently
          • 2 Alpha Glucose molecules join to make maltose (a disachharide)and hundreds of molecules join to form starch & glycogen (polysaccharides)
          • Hundreds of Beta Glucose molecules can be joined to make cellulose which is a polysaccharide.
      • Disaccharides(Molecules made by joining 2 single sugars together)
        • 2 a glucose molecules can be joined through condensationto make maltose, which is a double sugar.
        • During condensation, water is removed by losing the OH from c1 of one alpha glucose molecule and H from c4 of the second a glucose molecule.
      • Polysaccharides (Molecules made by joining many simple sugars together
        • Starch is an energy source in plants. It's a mixture of 2 polysaccharids (amylose and amylopectin. Amylose is a long chain of a-glucose joined by 1,4 glycosidic  bonds formed by condensation. It's formed in a helix
        • Glycogen is an energy store in animals, it's a polymer of a-glucose and formed by 1,4 glycosidic bonds formed by condensation. It's branched making it more compact, the branches are made by 1,6 glycosidic bonds
        • Cellulose is structural and found in plant cell walls. It's a polymer of B-Glucose joined by 1,4 Glycosidic bonds formed by condensation.Every second molecule is rotated 180 degrees. It makes them staight and unbranched.
          • This makes cellulose stright and unbranched and allows them to line up to make microfibrils containing ~70 cellulose molecules which are cross-linked by H bonds which are weak forces.
            • Microfibrils are held by H bond to form macrofibrils. Cellulose is insoluble and very strong.
    • Testing for sugars
      • All monosaccharides and many disaccharidesare reducing sugars. They can add electrons with other molecules (reduction)
      • When  a reducing sugar is heated, with Bendicts solution (CuS04 : Cu2+) the sugars reuces copper sultphate to form a brick red ppt of copper oxide.
      • To test for a non reducing sugar, do the Benedicts test, boil sample with HCl acid, cool sample, and neutralise HCl with Sodium hydrogen carbonate and do Benedicts again. Brick red PPT indicates that reducing sugars are present. Sucrose is an non reducing sugar.
      • A quantitative test tells you how much reducing sugar is present. To do it, make up standards and do the benedicts test on it. Filter off the ppts and measure % transmission. Plot a calibration curve. Do benedicts on samples, filter & measure & transmission and use CC convert % transmission.

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