Factors Affecting Enzyme Activity: Temperature and Substrate

Overview

Recall questions on Temperature and Substrate.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Why does the rate of an enzyme-controlled reaction increase as temperature rises towards the optimum?

   Model answer

   Both enzyme and substrate molecules gain kinetic energy and move faster, so they collide more often and with more energy, forming more enzyme–substrate complexes per unit time.

2. 2

   By roughly how much does the rate of an enzyme-controlled reaction change for a 10 °C rise in temperature below the optimum?

   Model answer

   The rate approximately doubles for every 10 °C rise.

3. 3

   Define the optimum temperature of an enzyme.

   Model answer

   The optimum temperature is the temperature at which the enzyme catalyses its reaction at the greatest rate.

4. 4

   What happens to an enzyme when it is heated well above its optimum temperature?

   Model answer

   The increased vibration breaks the hydrogen and ionic bonds holding the tertiary structure, so the active site changes shape, the substrate can no longer bind, and the enzyme is denatured.

5. 5

   Is denaturation reversible?

   Model answer

   No, denaturation is permanent, because the original bonds between R groups do not re-form and the active site cannot recover its shape.

6. 6

   Why does the rate fall very steeply above the optimum rather than declining gradually?

   Model answer

   Above the optimum the enzyme molecules are progressively denatured, so active sites are lost altogether rather than merely working more slowly.

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