An enzyme has an optimum temperature at which its reaction proceeds at the highest rate.
Below the optimum
At low temperatures, enzyme and substrate molecules have less kinetic energy, so their movement is slower and collisions occur less often.
- Substrates encounter enzyme active sites less frequently.
- Successful collisions are less common.
- Fewer enzyme-substrate complexes form per unit time.
- The lower energy of collisions also makes reaction less likely.
Increasing temperature
Raising the temperature towards the optimum increases kinetic energy. Enzyme and substrate molecules move faster and collide more often, increasing successful collisions and enzyme-substrate complex formation.
Above the optimum
At sufficiently high temperatures, interactions that help hold the enzyme's tertiary structure together begin to break. The enzyme changes conformation and its active site loses its normal shape.
Substrates then bind less successfully, so fewer enzyme-substrate complexes form and the rate falls rapidly. When the active site has changed enough to prevent substrate binding, the enzyme is denatured.
Exam Tip: Explain the rising part of a temperature-rate curve using kinetic energy, successful collisions and enzyme-substrate complex formation. Explain the fall above the optimum using changes to tertiary structure and denaturation of the active site.