Factors affecting enzyme activity

Overview

How temperature, pH, enzyme concentration and substrate concentration change the rate, the temperature coefficient Q10, and why serial dilutions are used.

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

   Explain how temperature affects enzyme activity above and below the optimum.

   Model answer

   Increasing temperature increases enzyme activity up to the optimum; beyond this, the enzyme denatures and activity decreases.

2. 2

   Why does enzyme activity decrease when pH deviates from the optimum?

   Model answer

   Deviations from the optimum pH cause changes in the shape of the active site, reducing enzyme activity.

3. 3

   Under what condition does increasing enzyme concentration increase the rate of reaction?

   Model answer

   Increasing enzyme concentration increases the rate of reaction when substrate is in excess.

4. 4

   Explain why the rate of an enzyme-catalysed reaction plateaus at high substrate concentrations.

   Model answer

   At high substrate concentrations, all active sites become saturated, so adding more substrate cannot increase the rate further.

5. 5

   Define the temperature coefficient Q₁₀.

   Model answer

   Q₁₀ is the factor by which the rate of a reaction increases when the temperature is raised by 10°C.

6. 6

   State the formula used to calculate Q₁₀.

   Model answer

   Q₁₀ = R₂ / R₁, where R₁ is the rate at the lower temperature and R₂ is the rate at a temperature 10°C higher.

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