biology-enzymes

• what is a catalyst

  • Increase the rate of a chemical reaction  
  • By reducing the activation energy and providing an alternative pathway for the reaction to occur 
  • They are not used up during reactions 
• what is an enzyme

  • Globular proteins  
  • Increase the rate of reaction  
  • Without enzyme action reactions would not happen at the rate required  
  • Biological catalysts  
• what is the structure of enzymes

  Structure is determined by the 3D tertiary structure of a protein  

  • Reaction takes place in the active site  
  • Enzymes are specific to their substrate so will not bind with an uncomplimentary substrate  
  • During a reaction, the enzyme binds to the substrate to form an enzyme-substrate complex  
• describe the lock and key model of enzyme action

  The substrate fits into the active site of the enzyme molecule  
• describe the induced fit model of enzyme action

  When a substrate moves towards the enzyme, the active site changes shape slightly to accommodate the substrate  

  • This distorts the enzyme into forming the transition state and so speeding up the reaction  
• how does temperature affect enzyme activity

  • enzymes only work at an optimum temperature if the temperature is too high or too low then they start to denature so the biological reactions would happen at a slower rate.
  • Up to the optimum temperature the rate increases as there is more kinetic energy, so the enzymes and substrates collide more often  
• how does ph affect enzyme activity

  • optimum ph of about 7-8 the -
  • change in ph affects the charge of the amino acids at the active site so the active site changes shape
  • so that the complimentary substrate can no longer bind to the active site  
• how does enzyme concentration affect enzyme activity

  • if the enzyme concentration increases the rate also increases as there are more enzymes available to catalyse the reaction.
  • At high concentrations of enzymes, the substrate is rate liming as there are less substrates for the enzyme to bind to this causes the rate to stop increasing  
• how does substrate concentration affect enzyme activity

  more substrate means more collisions between the enzyme and the substrate so more e-s complexes so an increased rate of reaction  
• what is vmak

  the maximum reaction rate at infinate substrate concentration
• what is Km

  the substrate concentration that gives a rate at half vmak
• describe competitive inhibitors

  • Similar structure to the substrate so can bind to the enzyme blocking the actual substrate. This lowers the rate of reaction 
  • No effect on vmak so the rate can approach a normal rate if the substrate concentration is increased high enough  
• describe non-competitive inhibitors

  • Different structure to the substrate  
  • Binds to the allosteric site on the enzyme changing the 3D tertiary structure so the substrate is no longer complimentary  
• describe reverisble and non-reversible inhibitors Inhibitors that can be

  • washed out are called reversible inhibitors  
  • Inhibitors that cannot be washed out are called non-reversible inhibitors   
• what are allosteric effectors 


  • Activity of enzymes is controlled by the allosteric site located on the enzyme  
  • The place where non-competitive inhibitors bind to 
  • Generally activated by the substrate of the pathway and inhibited by the product of the pathway so only turning the substrate on when it is needed   
• what are some applications of enzymes

  • Pregnancy tests  
  • Blood glucose tests  
  • Biological washing powder  
  • Drugs  
  • Food manufacturing