Enzymes and temperature
Explain a rate curve using collisions and changes in protein structure.
What you will learn
- Explain why temperature initially increases enzyme activity.
- Distinguish denaturation from low-temperature inactivity.
Enzymes catalyse reactions
Enzymes are biological catalysts. Their active sites interact with particular substrates, lowering the activation energy for a reaction. An enzyme is not used up each time it catalyses a reaction.
As temperature rises over a suitable range, particles have more kinetic energy and successful encounters become more frequent. This can increase the reaction rate.
High temperatures change the active site
Beyond a suitable range, bonds maintaining the enzyme's shape can be disrupted. The active site's shape changes and the substrate can no longer interact effectively. This is denaturation and explains a sharp decrease in activity.
Low temperature generally slows collisions without causing the same structural damage. An optimum temperature depends on the enzyme and conditions; 37°C is not a universal optimum for every enzyme.
Worked example
An enzyme's rate increases up to 40°C but falls sharply at 65°C. Explain both parts of the trend.
Show the worked solution
- Initially, higher kinetic energy increases the frequency of effective enzyme–substrate encounters.
- At high temperature, the enzyme's structure changes.
- The altered active site reduces successful substrate binding and catalysis.
Answer Faster encounters initially; denaturation at high temperature
Common mistakes
- Do not say an enzyme is killed: it is a molecule, not a living organism.
- A slower reaction in cold conditions does not by itself demonstrate denaturation.
What can you explain now?
Why can an enzyme often work again after being warmed from 5°C to its optimum?
Compare with the explanation
Its structure may have remained intact
The low temperature slowed molecular motion. Warming increases encounters without needing to repair a denatured active site.
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