Enzyme Action

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Enzymes as Catalysts

  • catalysts alter the rate of reaction without permenantly changing 
  • enzymes dont make reactions happen they just alter the speed 
  • an inital boost of energy is needed to start the reaction, this is known as ACTIVATION ENERGY 
  • enzymes lower the activation energy and and allow the reactions to take place at a lower temperature 
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Enzyme Structure

  • the enzyme molecule is large, but only a small region is functional 
  • this is the ACTIVE SITE, a hollow depression in the larger enzyme molecule 
  • the molecule on which the enzyme acts is called a SUBSTRATE 
  • this fits neatly into the active site forming an ENZYME SUBSTRATE COMPLEX 
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Lock and Key Model

  • a substrate will only fit the active site of one particular enzyme 
  • enzymes are specific in the reactions that they catalyse 
  • the shape of the substrate exactly fits the active site of the enzyme 
  • one limitation is that the active site is a rigid structure 
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Induced Fit Model

  • rather than being rigid, the enzyme changes its shape slightly to fit the substrate 
  • the enzyme is flexible and can mould itself 
  • the enzyme has a general shape but alters in the presence of a substrate 
  • the change in shape puts pressure on the substrate 
  • this strain distorts the bond and lowers the activation energy needed to break the bond 
  • and change in the enzymes environment is likely to change its shape 
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