Investigate and describe the effect of changes in temperature and pH on enzyme activity.

5.1 Enzymes – Effect of Temperature & pH

Enzymes are protein “workers” that speed up chemical reactions in our bodies. They work best under specific conditions. In this lesson we’ll explore how changes in temperature (🌡️) and pH (🧪) affect enzyme activity.

Key Concepts

• Enzymes are catalysts: they lower the activation energy $E_a$ of a reaction.
• Optimal temperature and pH give the highest activity.
• Too high or too low temperature/pH denatures the enzyme, reducing activity.
• Temperature and pH influence the enzyme’s 3‑D structure and the charge on its active site.

Temperature and Enzyme Activity

Think of an enzyme as a lock and the substrate as a key. At the right temperature the lock is flexible enough to open, but not so loose that it falls apart. The relationship can be described by the Arrhenius equation:

$$k = A e^{-E_a/(RT)}$$

Where $k$ is the reaction rate, $A$ is a constant, $E_a$ is the activation energy, $R$ is the gas constant, and $T$ is temperature in Kelvin.

pH and Enzyme Activity

pH is a measure of acidity: $$pH = -\log[H^+]$$. Enzymes have an optimal pH where the active site has the correct charge to bind the substrate. Outside this range, the enzyme’s shape changes.

Common Experiments

1. Prepare a buffer solution at different pH values.
2. Add a fixed amount of enzyme (e.g., catalase) to each buffer.
3. Introduce a substrate (e.g., hydrogen peroxide) and measure the rate of gas evolution (bubbles).
4. Record the time taken for a fixed volume of gas to be produced.
5. Plot a graph of pH vs. activity to find the optimum.

Exam Tips