The diagram below shows the rate of an enzyme controled reaction. The solid line indicates the normal relationship between rate and substrate concentration and the dotted line indicates the relationship when a competitive inhibitor is added.  


a.i)   Explain how a competitive inhibitor acts  
  • It is similar in shape to the substrate
  • Therefore fits into the active site
  • Thus blocking it preventing substrate entering and slowing reaction rate (any 2)
  ii)  Explain why in the graph above the inhibitor is a competitive inhibitor?  
  • The graph shows that at high substrate concentration the effect of the inhibitor is removed
  • This is because as soon as an active site becomes free it is filled with another substrate molecule
 The graph below shows the relationship between rate of reaction and temperature of most enzyme reaction.  


b.    Explain why the relationship is that shown on the graph.  
  • Initially as the temperature increases the amount of kinetic energy of the particles increases
  • Therefore there are more successful collisions per unit time
  • This continues until the rate is at its greatest (the optimum temperature)
  • At temperatures higher than this Hydrogen bonds holding the polypeptide chains together begin to break
  • This affects the tertiary structure of the enzyme (denatures it)
  • This changes the shape of the active site
  • Substrate can no longer fit, therefore rate decreases
  • This continues until 100% of the enzyme molecule are denatured and the rate of reaction falls to zero

 (any five)