4- enzymes

• enzymes 


  = biological catalysts, which speed up the rate of reaction.

  • by decreasing the activation energy by providing an alternative pathway which the energy needed can be reached sooner.
• lock and key hypothesis 


  -the enzymes active site is complementary to the shape of a specific substrate molecule.

  -when the substrate is bound to the active site, an enzyme- substrate complex is formed.

  -the substrate then reacts and the product is formed in an enzyme- product complex.

  -the product is then released, leaving the enzyme unchanged.
• induced-fit hypothesis 


  = the substrate isn't complementary but can fit into the active site.

  -active site of the enzyme changes shape slightly as the substrate enters.

  -the initial interaction between the enzyme and substrate is relatively weak, these rapidly induce changes to the enzymes tertiary structure that strengthen binding, putting strain on the substrate molecule.

  -this can weaken a particular bond in the substrate, therefore lowering the activation energy.
• intracellular enzymes

  = enzymes that act within a cell.

  • synthesis of polymers from monomers. eg: making polysaccharides from glucose requires enzymes.
  • hydrogen peroxide is toxic, enzymes catalase breaks it down into oxygen.
  • eg: helicase and polymerase.
• extracellular enzymes 


  = enzymes that work outside the cell that made them.

  • make use of polymers for nutrients.
  • eg: amylase, protease.
• digestive enzymes 


  = large molecules have to be digested into small molecules ot they can be absorbed into the bloodstream.

  • starch- maltose (amylase= salivary gland, pancreas) maltose- glucose ( maltase= small intestine)
  • protein- amino acids (protease/ trypsin= pancreas)