Enzymes

• Enzymes are all tertiary proteins with globular shape which has a pocket or cleft area which has a specific 3D shape called an active site where the reaction takes place.
• Enzymes act as biological catalysts – proteins that speed up metabolic reactions without being used up. 
• Enzymes provide an alternative pathway during a reaction.
• Enzymes are specific- they only catalyse one shape of substrate.
• The specific substrate has a complementary shape to the active site of the enzyme
• The activity of enzymes is affected by by temperature and pH.
• Enzymes are very important in digestion as they hydrolyse (break bonds using water) polymers into monomers. E.g. Polypeptides into amino acids. 
• An individual cell contains over a 1000 different enzymes which are involved in metabolic reactions such as hydrolysis reactions in digestion and photosynthesis and respiration. 
• The extra energy that is required to enable a reaction to occur is known as the activation energy. 
• Enzymes are biological catalysts i.e. proteins that are able to lower the activation energy of a reaction to allow it to proceed more quickly at lower temperatures in the body so that molecules can be broken down and new ones formed.
• Lock and Key model- Enzymes have a specific shaped active site which is complementary to the shape of the substrate molecules being used in the reaction.
• Induced fit model:

  • The substrate is not complementary.
  • It collides and binds with the active site.
  • The active site changes shape to fit more closely and becomes complementary.
  • It is held in place by oppositely charged R groups.
  • The tertiary structure of the enzyme changes.
• Induced Fit model:

  • An enzyme- substrate complex is formed.
  • A change in the shape of the enzyme places a strain on the bonds in the substrate.
  • This strain lowers the activation energy needed for the reaction to occur.
• Induced Fit model:

  • An enzyme- product complex forms.
  • The product no longer fits into the active site.
  • The product is released and the enzyme is able to catalyse another reaction.