factors affecting

• What 4 factors affect enzyme activity?

  1. temperature
  2. pH
  3. enzyme concentration
  4. substrate concentration
• What happens when temp increases?


  the rate of an enzyme-controlled reaction increaes
• what does more heat mean?

  more kinetic energy = molecules move faster = enzymes more likely to collide with the substrate molecules

  the energy of these collisions increases = each collision is more likely to result in a reaction
• what does the reaction do if the temp gets too high?

  the reaction stops
• What does the rise in temp make the enzyme's molecules do?

  vibrate more
• What happens if the temp goes above a certain level?

  the vibration of the enzymes molecules breaks some of the bonds that hold the enzyme in shape
• what do all enzymes have?

  an optimum pH value
• what pH do most human enzymes work best at?

  pH 7 (but there are exceptions)
• what pH does pepsin works best at?

  acidic pH 2 which is useful because its found in the stomach
• What can be found above and below the optimum pH?

  Above and below the optimum pH, the H+ and OH- ions found in acids and alkalis can mess up the IONIC BONDS and HYDROGEN BONDS that hold the enzyme's tertiary structure in place = active site changes place = enzyme is denatured
• explain how enzyme conc affects the rate of reaction?

  More enzyme molecules found in solution = more likely a substrate molecule is to collide with one and form an E-S complex
• what does increasing the conc of an enzyme do?

  increases the rate of reaction
• when does increasing enzyme conc have no further effect?

  • if the amount of substrate is limited
  • there comes a point when there is more than enough enzyme molecules to deal with all the available substrate
  • so adding more enzyme has no further effect
• how much does substrate conc affect the rate of reaction?


  affects rate of reaction up to a point
• the higher the substrate concentration....?

  the faster the reaction- more substrate molecules = collision between substrate and enzyme is more likely = more active sites will be used.
• substrate conc only increases rate of reaction until when?

  until a 'saturation' point
• what happens after the saturation point (substrate conc)?

  There are so many substrate molecules that the enzymes have about as much as they can cope with (all active sites full) and adding more makes no difference
• what does substrate conc do with time?

  decreases with time (unless more substrate us added to the reaction mixture) so if no other variables are changed . the rate of reaction also DECREASES OVER TIME

  • this makes the INITIAL rate of reaction the highest rate of reaction
• what is the affect of increasing enzyme conc?


  = more likely that a substrate molecule will collide with on and form an E-S complex , = increased rate of reaction