3.1.4.2 enzymes

• Polymers of amino acids joined by peptide bonds. Has the same structure sequence as a protein
• Induced fit model

  The substrate and active site should have a complementary shape to collide and bind to form an enzyme-substrate complex. These, however, are not perfectly complementary. The active site will mold around the substrate to form a complementary fit.

  Each enzyme is specific to the substrate(s)
• Why do enzymes lower the activation energy?

  Bringing substrates close together in the active site, preventing them repelling each other, so they bind more readily

  Putting strain/tension on the substrate when it is in the active site, so its bonds break more readily
• Factors affecting rate of enzyme activity

  Temperature

  pH

  Substrate concentration

  Enzyme concentration
• If the shape of the active site of an enzyme changes, the rate of reaction will decrease. Substrates can no longer bind and enzyme-substrate complexes cannot form
• Explain why rate of reaction increases with increasing collisions between enzymes and substrates?

  More substrates bind with active sites

  More E-S complexes

  More products
• Explain why changing the shape of the active site will decrease the rate of reaction?

  Bonds break

  active site denatures/loses its tertiary structure

  shape no longer complementary to substrate

  Fewer/no E-S complexes form
• Competitive inhibitors

  Inhibitor has a similar shape to the substrate, so will bind to the enzymes active site. This blocks the substrate, preventing it from binding, fewer enzyme substrate complexes are formed. The rate of reaction decreases

  
• Non-competitive inhibitors

  Binds to allosteric site of the enzyme, not the active site. The tertiary structure of the enzyme changes along with the active site. Substrates cant enter or bind to the enzyme so fewer E-S complexes form. Rate of reaction decreases

  These inhibitors can also be used to make a non-complementary active site complementary to its substrate

  
• Examples of measuring enzyme activity

  • Gas volume collected
  • Mass change
  • Colour change