Enzymes and temperature
Explain the rise and fall of enzyme activity without confusing denaturation with low temperature.
Before you begin
- Cell reactions
- Reading a rate graph
Explain biological catalysis
An enzyme is a biological catalyst that increases reaction rate without being used up overall. Its active site interacts with particular substrates, helping lower the activation energy required for a reaction. Shape and chemical properties both matter. A simple lock-and-key drawing is useful, but enzymes are flexible molecules rather than rigid pieces of a puzzle.
Interpret temperature effects
At low temperatures, particles move more slowly and successful interactions are less frequent. Warming often increases rate up to an optimum under the tested conditions. Higher temperatures can disrupt the enzyme's structure so its active site no longer works effectively: denaturation. A low rate in the cold does not by itself mean the enzyme has been denatured.
Worked example
An enzyme reacts slowly at 10 °C, rapidly at 35 °C and very slowly after heating to 80 °C. Explain the pattern.
Show the worked solution
- The low-temperature sample has fewer successful enzyme-substrate interactions per second.
- At 35 °C, movement and successful interactions are greater under these conditions.
- Strong heating can alter the active site, reducing activity even if the sample is later cooled.
The rise reflects faster interactions; the sharp high-temperature fall is consistent with denaturation.
Try it yourself
What does an enzyme do to activation energy?
Common mistakes
- Enzymes do not all have the same optimum temperature or pH.
What can you explain now?
Why should pH be controlled in an investigation of temperature and enzyme activity?
Compare with the explanation
pH can independently affect the enzyme's activity and structure.
If both pH and temperature vary, either could explain the rate change. Keep pH comparable to isolate the temperature effect more clearly.
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