Function

• Active site

  • Specific substrates bind here to form an enzyme substrate complex
  • Has a specific shape that fits a specific substrate
  • complementary shape
• For a successful reaction, collisions must occur at the:

  • correct orientation
  • correct speed
• Enzyme specificity

  • complementary nature - substrate and active site
  • active site's shape is determined by tertiary/quaternary structure of enzyme
• Enzyme-substrate complex

  • formed temporarily before the enzyme catalyses the reaction and the products are released
• Lock and key model

  • active site is exactly complementary to substrate shape
  • enzyme is unchanged throughout reaction
• Induced fit model

  • enzyme and active site change shape slightly - CONFORMATIONAL CHANGE
  • this ensures an ideal binding arrangement
  • maximises ability to catalyse the reaction
• Activation energy

  • amount of energy needed for the substrate to become unstable enough for a reaction to occur
• Enzymes and activation energy

  • enzymes reduce stability of bonds in substrates to increase their reactivity
  • they put pressure on bonds inside the substrate
• Enzymes reduce activation energy

  • so high temperatures are not required
  • so high pressures are not required
• Cofactors

  non-protein compound required for activity to occur

  • coenzymes
  • activators
  • prosthetic groups
• Coenzyme


  • an organic cofactor
  • do not bind permanently
  • facilitate binding of a substrate to an enzyme
  • derived from vitamins
• Activators


  • inorganic, metal ions
  • temporarily bind
  • alters shape of the active site to make the reaction more feasible
• Prosphetic group


  • permanently attached to the enzyme
  • required for enzyme activity