Explain how end-product inhibition allows a cell to regulate the rate of a metabolic pathway.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In many biosynthetic pathways, the final product of the pathway acts as an inhibitor of an enzyme that catalyses an early step in the same pathway.
Model answer (4 marks)
The end‑product of a biosynthetic pathway binds to an allosteric site on the enzyme that catalyses an early, committed step in that pathway. This binding induces a conformational change that reduces the enzyme’s catalytic activity – an example of allosteric inhibition. When the concentration of the end‑product is high, the pathway is inhibited, so further synthesis of that product is slowed. Conversely, when the end‑product is consumed or its concentration falls, the inhibition is relieved and the pathway activity resumes. Thus end‑product inhibition provides a negative feedback mechanism that matches production to cellular demand.
Examiner tips
- Use the term ‘allosteric site’ and ‘allosteric inhibition’.
- Explain the cause (conformational change) and effect (reduced activity).
- Show the feedback loop: high product → inhibition; low product → relief of inhibition.
Common mistakes
- Confusing the enzyme with the product; not specifying the allosteric site.
- Failing to mention the negative feedback nature of the regulation.
Mark scheme (4 marks)
- The end-product of the pathway binds to an allosteric site on an enzyme that catalyses an early (committed) step in the pathway.
- Binding of the end-product causes a conformational change in the enzyme, reducing its catalytic activity (allosteric inhibition).
- When the concentration of the end-product is high, the pathway is inhibited, reducing further synthesis of that product.
- When the end-product is consumed / its concentration falls, inhibition is relieved and pathway activity resumes, acting as a negative feedback mechanism to match production to demand.
Key terms in this question
end-product inhibition · metabolic pathway
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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