Explain how enzymes can be denatured due to changes in the shape of the…

The idea

Enzymes are proteins, and their function depends on the precise three-dimensional shape of the active site. Changes in temperature or pH can alter the bonds holding the protein in shape. Above an optimum temperature, increased vibration disrupts these bonds, so the active site loses its complementary shape; the substrate can no longer fit, the enzyme–substrate complex cannot form and the rate of reaction falls. Extreme pH changes can do the same. This permanent loss of shape is denaturation — distinct from simply slowing down. A useful method: state the factor, explain how it alters bonds and shape, state the substrate no longer fits the active site, and conclude the reaction rate falls because no complexes form.

What earns the marks

• Enzymes are proteins whose active site shape depends on bonds holding the molecule together.
• Changes in temperature or pH can break or alter these bonds.
• The active site changes shape and is no longer complementary to the substrate.
• The substrate cannot bind, so enzyme–substrate complexes cannot form.
• Denaturation is a permanent change in the enzyme's shape, reducing the rate of reaction.

Common mistakes and how to put them right

• Saying the enzyme is 'killed'.

  Put it right: Correct this to saying the enzyme is denatured, since enzymes are not alive.

• Confusing denaturation with the enzyme simply working more slowly at low temperature.

  Put it right by stating denaturation is a change in shape of the active site.

• Stating the substrate changes shape instead of the enzyme.

  Put it right by explaining that the active site loses its complementary shape.

Exam tips

• Name the factor (high temperature or extreme pH) and explain the effect on bonds before describing the shape change.
• Use the chain: bonds disrupted → active site shape changed → substrate no longer complementary → no complexes → rate falls.
• Distinguish clearly between denaturation (permanent shape change) and reduced activity for other reasons.