IGCSE Biology B5

Describe what enzymes are.

Proteíns that act as biological catalysts in all metabolic reactions.

They speed up chemical reactions without being changed or used up.

State three properties of enzymes.

Enzymes are:
– Proteins
– Catalysts that speed up reactions
– Reusable (not changed or used up in the reaction)

Explain why enzymes are essential for living organisms.

Enzymes are necessary for all metabolic reactions, which sustain life by allowing biological processes to occur quickly enough to support life.

Explain enzyme action with reference to substrate, product, active site, and enzyme–substrate complex.

The substrate binds to the enzyme’s active site, forming an enzyme–substrate complex. The reaction occurs, producing products, which are released. The enzyme remains unchanged and can be reused.

Describe the steps in enzyme action.

Enzyme and substrate move randomly and collide.
Substrate binds to the enzyme’s active site, forming an enzyme–substrate complex.
The reaction occurs.
Products are released.
The enzyme is unchanged and can be reused.

Explain enzyme specificity.

Each enzyme has an active site with a specific shape that is complementary to the shape of its substrate. Only one specific substrate can fit and bind to the enzyme.

Explain the effect of low temperature on enzyme activity.

Enzyme activity is low because enzymes and substrates have less kinetic energy, so fewer effective collisions occur and fewer enzyme–substrate complexes are formed.

Explain the effect of increasing temperature up to the optimum on enzyme activity.

As temperature rises, enzymes and substrates gain kinetic energy, leading to more frequent and effective collisions. This increases enzyme–substrate complex formation and reaction rate.

Explain what happens to enzymes at temperatures above the optimum.

Enzymes become denatured. The shape of the active site changes, so it is no longer complementary to the substrate. Enzyme–substrate complexes cannot form, and the reaction stops.

Define the term denaturation.

Denaturation is the irreversible change in the shape of an enzyme’s active site, preventing it from binding its substrate.

Explain the effect of pH on enzyme activity.

Enzymes work best at their optimum pH. If pH is too high or too low, the enzyme becomes denatured, and the active site loses its shape, preventing enzyme–substrate complexes from forming