Explain how allosteric regulation allows an enzyme to act as a metabolic switch, using the concept of cooperativity where relevant.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Allosteric regulators bind to a site other than the active site (the allosteric site), inducing a conformational change in the enzyme.
The conformational change alters the shape of the active site, either increasing activity when an activator binds or decreasing activity when an inhibitor binds, thereby acting as a metabolic switch.
Many allosteric enzymes are multimeric; binding of a regulator to one subunit induces conformational changes in neighbouring subunits – a phenomenon known as cooperativity.
This mechanism is often used for end‑product (feedback) inhibition, where the pathway’s final product binds to an earlier allosteric enzyme to shut down the pathway and conserve resources.
The conformational change alters the shape of the active site, either increasing activity when an activator binds or decreasing activity when an inhibitor binds, thereby acting as a metabolic switch.
Many allosteric enzymes are multimeric; binding of a regulator to one subunit induces conformational changes in neighbouring subunits – a phenomenon known as cooperativity.
This mechanism is often used for end‑product (feedback) inhibition, where the pathway’s final product binds to an earlier allosteric enzyme to shut down the pathway and conserve resources.
Examiner tips
- Use the term ‘allosteric site’ and ‘conformational change’ to show understanding of the mechanism.
- Explain how the change can ‘switch on’ or ‘switch off’ activity – this shows the ‘switch’ concept.
- Mention multimeric enzymes and cooperativity to hit the extra point.
- Include the example of end‑product inhibition to demonstrate a common regulatory strategy.
Common mistakes
- Confusing the active site with the allosteric site; students often say the regulator binds to the active site.
- Failing to mention that the change can either activate or inhibit – only stating one effect.
- Not recognising cooperativity as a result of subunit interaction in multimeric enzymes.
Mark scheme (4 marks)
- Allosteric regulators bind at a site other than the active site (the allosteric site), causing a conformational change in the enzyme.
- This conformational change alters the shape of the active site, either increasing (activator) or decreasing (inhibitor) enzyme activity, effectively switching catalytic activity on or off.
- Many allosteric enzymes are multimeric (have multiple subunits); binding of a substrate or effector to one subunit induces conformational changes in adjacent subunits — this is cooperativity.
- Allosteric regulation commonly operates as end-product (feedback) inhibition, where the final product of a metabolic pathway inhibits an earlier allosteric enzyme, preventing overproduction and conserving cellular resources.
Key terms in this question
allosteric regulation · cooperativity
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Enzymes and metabolism questions
- Explain how the induced fit model accounts for the specificity and catalytic act…
- Explain how changes in temperature affect the rate of an enzyme-catalysed reacti…
- Explain how the concentration of substrate affects the rate of an enzyme-catalys…
- Explain how covalent modification of an enzyme can regulate its activity, using …
- Explain how changes in pH affect the rate of an enzyme-catalysed reaction, with …
- Explain how immobilised enzymes differ from free enzymes in their properties and…