9.2.4 Enzymes & Temperature/ pH

• Enzymes


  Their action is affected by temperature

  
• Enzymes


  • Have an optimum (best) temperature that they work at

  
• Enzymes at 0-30°C


  1. Enzymes do not have much kinetic energy

  2. Enzymes and substrates are moving around more slowly

  3. There are not many collisions between enzyme and substrate

  4. Fewer enzyme-substrate complexes

  5. The rate of enzyme activity is low

  
• Enzymes above 40°C


  1. The enzyme becomes denatured

  2. The active site changes shape

  3. The substrate no longer fits in the active site

  4. The enzyme and substrate are no longer complementary
• pH


  Enzymes have an optimum pH, the pH at which they work best

  
• Enzymes below and above optimum pH


  1. The enzyme is denatured

  2. The active site has changed shape

  3. The active site is not complementary to the substrate

  4. The substrate cannot fit into the active site
• Optimum pH for this enzyme

  pH 2

  
• At a higher pH


  The active site has changed shape, the enzyme has denatured, the substrate and enzyme are no longer complementary
• Different enzymes have different optimum pHs
• Optimum pH depends on where enzymes are found in the digestive system


  Eg. Pepsin (stomach) has optimum pH 2, Trypsin (small intestine) has optimum pH 9

  
• Gastric juice in the stomach contains hydrochloric acid
• One function of hydrochloric acid

  To create a low pH for pepsin to work