Models of Enzyme Action

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  • Models of Enzyme Action
    • Lock & Key Model
      • suggests substrate combines with enzyme at active site in precise way
        • like the way lock & key fit
      • active site always exact complementary shape (at optimum temperature) so reactions are fastest in these conditions
      • following the reaction the products do not fit active site so escape leaving enzyme unaltered & free to react with more substrate
      • 1 limitation of model is that enzyme is considered rigid structure
        • scientists have observed that structure is not rigid
          • structure is flexible
    • Induced Fit Model
      • suggests that substrate & active site are not exactly complementary to begin with
        • when substrate binds with enzyme it induces changes in enzyme structure
      • amino acids that make up enzyme's active site are moulded in to precise formation to wrap round substrate
        • form enzyme-substrate complex
        • active site changes shape to become complementary
      • strained fit between active site & so reduces activation energy needed to break bond
      • explains how binding of other molecules can affect enzymes' shape & activity
        • provides explanation for how activation energy is lowered


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