3.1 Biological molecules AQA A Level Biology

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  • Biological molecules
    • Monomers and polymers
      • What are they?
        • Polymers are molecules made from a large number of monomers joined together
        • Monomers are the smaller units from which larger molecules are made
          • Monosaccharides, amino acids and nucleotides are examples of monomers
      • Condensation
        • A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water
      • Hydrolysis
        • A hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule
    • Carbohydrates
      • Saccharides
        • Mono=one      A single sugar molecule. e.g. Glucose, galactose and fructose
        • Di = two            A condensation reaction between two monosaccharides forms a glycosidic bond and a disaccharide
          • maltose is a disaccharide formed by condensation of two glucose molecules
          •  sucrose is a disaccharide formed by condensation of a glucose molecule and a fructose molecule
          • lactose is a disaccharide formed by condensation of a glucose molecule and a galactose molecule
        • Poly = many     Polysaccharides are formed by the condensation of many glucose units
          • Glycogen and starch are formed by the condensation of alpha-glucose
          • Cellulose is formed by the condensation of beta-glucose
      • Glucose
        • Glucose has two isomers
          • alpha-glucose
          • ?-glucose
    • Lipids
      • Triglycerides
        • formed by the condensation of one molecule of glycerol and three molecules of fatty acid
        • A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond
          • Phospholipids
            • one of the fatty acids of a triglyceride is substituted by a phosphate-containing group
      • Phospholipids
        • one of the fatty acids of a triglyceride is substituted by a phosphate-containing group
      • The R-group of a fatty acid may be saturated or unsaturated
        • Saturated = no double carbon bond (c=)
        • unsaturated = contains a double bond (c=)
      • the emulsion test for lipids
    • Proteins
      • General properties of proteins
        • Amino acids are the monomers from which proteins are made
        • need to know the structure
        • peptide=one     dipeptide=two polypeptide=many
          • A condensation reaction between two amino acids forms a peptide bond 
          • A functional protein may contain one or more polypeptides
        • hydrogen bonds, ionic bonds and disulfide bridges maintain the structure of proteins
      • Many proteins are enzymes
        • Each enzyme lowers the activation energy of the reaction it catalyses
        • models of enzyme action
          • Lock and key theory
          • Induced fit model
        • How they form complexes?
          • the active site of the enzyme is complementary in shape to the substrate
          • factors affecting this
            • enzyme concentration
            • substrate concentration
            • pH
              • calculate pH, using the formula: pH = ?log10 H+ 
            • Temperature
            • inhibitors
      • the biuret test for proteins

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