Rate: Temperature (Cambridge (CIE) AS Biology): Revision Note

Rate: temperature

• Enzymes have a specific optimum temperature

  • This is 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