Enzymes (cont.2)

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  • Enzymes
    • Cofactor
      • Prosthetic groups
        • The enzyme carbonic anhydrase contains a ZINC ion as a prosthetic group
        • a cofactor that is permanently bound (covalently) to an enzyme
      • the presence of certain ions that may temporarily bind to enzyme or substrate may ease the formation of ES complexes and increase the rate of reaction
        • co-substrates - they and the substrate together form the complementary shape to the active site
      • Chloride ions are needed for amylase
      • Coenzymes
        • Are chemically changed during a reaction and need to be recycled to their original state
        • Many are water-soluble vitamins
        • Small organic non-protein molecules that bind temporarily to the active site
      • a substance that has to be present to ensure that an enzyme catalysed reaction takes place at an appropriate rate
    • Inhibitors
      • Competitive inhibition
        • The amount of inhibition depends on the relative concentration of substrate and inhibitor
          • Increasing substrate concentration dilutes the effect of the inhibitor
        • If the inhibitor binds irreversibly, it is an INACTIVATOR
        • substances that have a similar shape to the substrate and so compete to bind with the active site
          • form an enzyme-inhibitor complex that is catalytcally inactive
      • Non-competitive inhibition
        • reduces the maximum (initial) rate of reaction
        • the higher concentration of NCI's, the greater degree of inhibition because more enzymes are distorted
        • molecule attaches to an allosteric site, disrupting the tertiary structure and changing the active site shape
        • used in control of metabolic sequences
      • A substance that reduces or stops an enzyme controlled reaction
      • End product inhibition
        • product molecules stay tightly bound to the enzyme to prevent the enzyme from forming more produc
        • negative feedback regulation
    • Metabolic poisons
      • Cyanide
        • inhibits aerobic respiration and catalase
      • Snake venom
        • inhibits an enzyme in neuromuscular synapses, which keeps the muscles contracted = paralysis, suffocation
    • Medicinal drugs
      • Aspirin
        • inhibits enzymes that lead to higher sensitivity to pain
      • Protease inhibitors
        • competitively inhibit viral protease enzymes to prevent viral coats from being
  • (e) the need for coenzymes, cofactors and prosthetic groups in some enzyme-controlled reactions -To include Cl – as a cofactor for amylase, Zn2+ as a prosthetic group for carbonic anhydrase and vitamins as a source of coenzymes. (f) the effects of inhibitors on the rate of enzyme controlled reactions. To include competitive and non-competitive and reversible and non-reversible inhibitors with reference to the action of metabolic poisons and some medicinal drugs, and the role of product inhibition


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