Limiting Factors Affecting Enzymes: Temperature (AQA AS Biology): Revision Note

The effect of temperature

• 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:

  • Molecules move relatively slowly

  • There is a lower frequency of successful collisions between substrate molecules and the active site of the enzyme

  • Therefore, less frequent enzyme-substrate complex formation

  • Substrate(s) and enzyme 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:

  • Molecules move more quickly

  • There is a higher frequency of successful collisions between substrate molecules and the active site of the enzyme

  • Therefore, more frequent enzyme-substrate complex formation

  • Substrate(s) and enzyme 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

    • High temperatures cause the hydrogen bonds between amino acids to break, changing the conformation of the enzyme