What are the two main factors that affect enzyme activity?

  1. Temperature


  1. pH

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What does the term 'optimum' mean for enzyme temperature?

The optimum temperature is the temperature that gives the highest enzyme activity.

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What would the graph above look like for an enzyme-catalysed reaction? 

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What is the optimum temperature of enzymes in the human body? 

Around 37-38°C.

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Use the graph above to describe and explain how temperature affects rate of reaction.

  1. At first rate of reaction increases with temperature, as the particles gain more kinetic energy, so collide more frequently with enough energy to react.
  2. The rate of reaction reaches its peak around 37°C, which is the optimum temperature.
  3. Above 37°C the rate of reaction starts to fall - this is because the high temperatures break some of the bonds holding the enzyme together, changing the shape of active site and meaning it may no longer be as complementary to the substrate.
  4. At around 45°C the enzymes denatures, which means it can't form any enzyme-substrate complexes at all, and so the rate of reaction reaches 0.

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What is pH?

A measure of the hydrogen ion concentration, or a measure of acidity.

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Explain how high or low pH can cause an enzyme to denature.

  1. High or low pH can break the bonds holding the enzyme together.
  2. This causes the enzyme and its active site to change shape.
  3. This means the enzyme's active site will no longer be complementary to the substrate.
  4. This means it can no longer form an enzyme-substrate complex. 

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What would the above graph look like for a reaction catalysed by amylase (optimum pH of 7)?

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