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Key Stage 4: Enzymes

Author: Pete Sewell

Higher candidates

Factors affecting enzyme activity
Enzyme catalysed reactions, like most chemical reactions, are affected by three different variables, which are:

  • temperature
  • concentration
  • surface area

As you saw earlier in this lesson, the activity of enzyme catalysed reactions is affected by temperature. Look at the graph again.

When they are too warm the enzymes denature and no longer work. When cold they work slowly. The optimum temperature for most enzymes is around 37° C. This is normal body temperature.

Effect of pH conditions
The human gut produces other substances that affect the pH. The stomach produces hydrochloric acid and the gall bladder produces bile, which contains alkaline bile salts. The enzymes secreted in these two regions work best in the pH conditions found there. This is shown in the graph below.

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