Enzymes

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  • Enzymes
    • Factors affecting enzyme reaction rates
      • Temperature
        • Increased temperature
          • Increased kinetic energy
            • Increased movement of substrate and enzymes
              • Greater chance of collision, greater rate of reaction
        • Temperatures that are too high can break the bonds in the tertiary structure of the enzyme
          • This changes the shape of the active site, making it no longer specific to the substrate
      • pH
        • A change in the amount of hydrogen ions available causes the tertiary structure to change
          • This is because there are hydrogen bonds in the tertiary structure that may alter in the presence of more hydrogen ions
            • This changes the shape of the active site, making it no longer specific to the substrate
      • Substrate and enzyme concentration
        • Greater number of substrates, increased likelihood of collision with enzymes, increased rate of reaction
        • Greater number of enzymes, increased available active sites, greater likelihood of collision, increased rate of reaction
    • Competitive inhibition
      • A molecule or part of a molecule that is the same shape as the substrate attaches to active site of enzymes.
        • This reduces the availability of active sites for the substrate, and reduces the rate of reaction.
    • Non-competitive inhibition
      • Inhibitor binds to allosteric site.
        • This changes the tertiary structure and the active site changes shape. This means it is no longer specific to the substrate, and the enzyme is inhibited.
      • Example of a irreversible non-competitive inhibitor
        • PPIs - proton pump inhibitors, used to treat long term indigestion. Irreversibly block enzymes responsible for secreting hydrogen ions into stomach. This reduces the amount of hydrochloric acid in the stomach
      • Can be reversible or irreversible
    • End-product inhibition
      • Product of a reaction acts as an inhibitor to enzyme that produced it.
        • Negative feedback
      • E.g. in respiration, ATP is produced. When ATP levels are high, more ATP binds to the allosteric site on the PFK enzyme, preventing addditin of second phosphate group to lcuose
    • Co-factors
      • Non-protein 'helper' component. Inorganic.
        • Inorganic: obtained through diet,  calcium, iron, etc.
          • Amylase - catalyses breakdown of starch - requires cofactor of chloride.
    • Coenzymes
      • Non-protein 'helper' component. Organic. Derived from vitamins.
        • Vitamin B3 used to synthesise NAD coenzyme. This coenzyme is required for alcohol dehydrogenase to break down ethanol.
    • Prosthetic groups
    • Precursor activation
      • Many enzymes produced in inactive form, especially with enzymes that may harm the cell producing them.
        • Pepsinogen - originally inactive, the low pH activates enzyme.

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