Rate: Temperature (CIE A Level Biology)

• Enzymes have a specific optimum temperature – the temperature at which they catalyse a reaction at the maximum rate
• Lower temperatures either prevent reactions from proceeding or slow them down this is because:
  • Molecules move relatively slowly at lower temperatures
  • Therefore there is a lower frequency of successful collisions that occur between substrate molecules and the active site of the enzyme
  • So there are less frequent enzyme-substrate complexes formed
  • Substrates and enzymes collide with less energy, making it less likely for bonds to be formed or broken (stopping the reaction from occurring)
• Higher temperatures speed up reactions this is because:
  • Molecules move more quickly at higher temperatures
  • Which results in higher frequency of successful collisions between substrate molecules and the active sites of enzymes
  • So there are more frequent enzyme-substrate complexes formed
  • Substrates and enzymes collide with more energy, making it more likely for bonds to be formed or broken (allowing the reaction to occur)
• However, as temperatures continue to increase, the rate at which an enzyme catalyses a reaction drops sharply, as the enzyme begins to denature:
  • Bonds (e.g. hydrogen bonds) holding the enzyme molecule in its precise shape start to break
  • This causes the tertiary structure of the protein (i.e. the enzyme) to change
  • This permanently damages the active site, preventing the substrate from binding
  • Denaturation has occurred if the substrate can no longer bind
  • Very few human enzymes can function at temperatures above 50°C
    • This is because humans maintain a body temperature of about 37°C, therefore even temperatures exceeding 40°C will cause the denaturation of enzymes

Denaturation of Enzymes Diagram

The effect of temperature on the rate of an enzyme-catalysed reaction. Enzyme activity will have an optimum temperature specific for each enzyme.