Rate: 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 slow
- Lower frequency of successful collisions between substrate molecules and active site of enzyme
- Less frequent enzyme-substrate complex formation
- Substrate 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
- Higher frequency successful collisions between substrate molecules and active site of enzyme
- More frequent enzyme-substrate complex formation
- Substrate 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 (eg. hydrogen bonds) holding the enzyme molecule in its precise shape start to break
- This causes the tertiary structure of the protein (ie. 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 causes the hydrogen bonds between amino acids to break, changing the conformation of the enzyme
The effect of temperature on the rate of an enzyme-catalysed reaction
Exam Tip
When answering questions about reaction rates for enzyme-catalysed reactions, make sure to explain how the temperature affects the speed at which the molecules (enzymes and substrates) are moving and how this, in turn, affects the number of successful collisions.
