Factor that Affect Enzyme Activity

  • Created by: Freja
  • Created on: 24-04-21 14:29
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  • Factors Affecting  Enzyme Activity
    • pH
      • Renaturation- if the pH returns to the optimum, from within the range, the protein will resume its normal shape and can catalyse the reaction again.
      • All enzymes have an optimum pH value, at which the rate of reaction is highest, and enzymes have a narrow optimum pH range. 
      • Most human enzymes work best at pH 7, but there are exceptions. Pepsin works best at pH2, which is useful because it's found in the stomach.
      • Outside of the optimum pH range, the H+ and OH- ions interact with the hydrogen and ionic bonds in the tertiary structure and so the active site is irreversibly changed.
      • This means that the reaction cannot form enzyme-substrate complexes, so no enzyme-product complexes are formed. 
      • The enzymes are denatured, and the reaction has stopped.
      • The graph is symmetrical, unlike the other graphs, and it shows the pH range at which the enzyme works and where the pH becomes too acidic and too alkaline.
    • Temperature
      • As the temperature increases, the kinetic energy of the enzyme and the substrate increases.
      • So, the enzymes and substrate molecules move faster, so the active sites and substrates are more likely to successfully collide more frequently, so are more likely to result in a reaction. 
      • This means that there are more enzyme-substrate complexes are formed and this increases the rate of reaction. 
      • This is why the graph increases until the optimum temperature. Above the optimum temperature, the rate of reaction decreases, hence the decrease in the graph. 
      • As the temperature increases the molecules vibrate more and above the optimum temperature the vibration breaks some of the bonds in the enzyme’s tertiary structure.
      • This causes the enzyme’s active site to change shape and so the substrate and the enzyme’s active site are no longer complemen-tary in shape. 
      • At this point the enzyme is denatured, so the curve decreases as the rate of reaction is decreased.
    • Enzyme Concentration
      • Given that the substrate is in excess, the rate increases proportionally to the enzyme concentration 
      • The more enzymes in a solution, the more likely substrate molecule is to collide with an active site of an enzyme and so more enzyme-substrate complexes are formed. 
      • This continues until all the active sites are used up and the maximum number of enzyme-substrate complexes have been formed.
      • This is because there is a limited amount of substrate, so adding more enzymes does not have a further effect. 
      • Therefore, increasing the concentration of enzyme is not the limiting factor and increasing the concentration of enzymes increases the rate of reaction.
      • Which is why the graph levels off, as it has reached its Vmax.
    • Substrate Concentration
      • As the concentration of substrate is increased, it means that the number of substrate molecules in a certain volume increases, therefore a collision is more likely. 
      • There is a higher rate of collision between the substrate and the active sites of enzymes, so there are more enzyme-substrate that are formed.
      • There is a steady increase as more substrate molecules are available, hence the linear part of the graph.
      • The rate of reaction increases and continues to increase until the reaction reaches its maximum.
      • At the maximum all the available active sites are occupied by the substrate particles, so no more enzyme-substrate complexes can be formed until either product is released or more enzymes are added.
      • When the graph levels off, all the active sites are full and adding more substrate will have no impact on the rate of reaction. This is where the graph curves, and so the enzyme concentration is the limiting factor.


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