Enzymes

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  • ENZYMES - tertiary globular proteins that are catalysts
    • Properties
      • speed up reactions
      • Not used up
      • not changed
      • they catalyst many reactions per second
    • Active sites
      • Lock and key theory
        • the unique shape of the active site and means that an enzyme can only catalyse one type of reaction. It forms an enzyme -substrate complex.
      • Lysozyme and the induced fit
        • Suggested that the enzyme shape alters slightly to accommodate the substrate.
    • Factors affecting rate of reactions
      • Temperature
        • Increased temp increases the kinetic energy of enzyme and substrate molecules and they collide with enough energy more often, increasing the rate of reaction. till its up to an optimum where it denatures.
          • When enzymes are denatured by high temp or extremities, their hydrogen and ionic bonds are broken.
      • Substrate concentration
        • Increases substrate concentration increases chance of successful collision between enzyme and substrate. The plateau is reached. All active sites are in use.
      • pH
      • Enzyme concentration
        • Increasing enzyme concentration increases chance of successful collision between enzyme and substrate. Theoretically rate will continue to rise, so long substrate is present in excess and there are no other limiting factors.
    • Inhibitors
      • Competitive inhibitors
        • have a molecular shape complementary to the active site. Similar to the substrate shape
        • Prevents the substrate from forming
      • Non- competitive inhibitors
        • Binds to the enzyme at an "allosteric site". This alters its overall shape, including the active site.
        • No enzyme - substrate complexes forming
        • As the inhibitor concentrationincreases
          • Competitive inhibitors
            • have a molecular shape complementary to the active site. Similar to the substrate shape
            • Prevents the substrate from forming
          • reduces the effect of the inhibitor, because more substrate molecules are present, the greater their chance of binding to the active sites, leaving fewer available for the inhibitor
          • more enzyme molecules are denatured and so the rate of reaction and final mass of product decreases.
    • Activation energy
      • Its the minimum energy required for molecules to react, breaking existing bonds in the reactants and making new ones.
      • Enzymes lower activation energy
      • By lowering activation energy, enzymes allow reactions to take place at the lower temp found in the cell

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