Explain how the products of enzyme-catalysed reactions accumulate in metabolic pathways, and outline how end-product inhibition prevents the overproduction of metabolites.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In metabolic pathways, a series of enzyme-catalysed reactions converts an initial substrate into a final product through several intermediate steps. The final product can regulate the activity of enzymes earlier in the pathway.
Model answer (4 marks)
In a metabolic pathway the product of one enzyme becomes the substrate for the next enzyme in the sequence. When the final end‑product accumulates to a high concentration it binds to an allosteric site on an earlier enzyme. This binding changes the shape of the enzyme’s active site, reducing its activity and preventing substrate binding. The negative feedback stops further production of the end‑product, preventing waste of resources and over‑production.
Examiner tips
- Use the term ‘allosteric site’ and ‘negative feedback’
- Show the sequence of reactions – product becomes next substrate
- Explain how binding changes the enzyme shape and activity
- Mention waste prevention and resource conservation
Common mistakes
- Confusing the end‑product with the substrate of the same enzyme
- Forgetting to mention the allosteric site
- Not linking the change in shape to reduced activity
Mark scheme (4 marks)
- In a metabolic pathway, the product of one reaction becomes the substrate for the next enzyme in the sequence.
- When the final end-product accumulates (at high concentration), it binds to an allosteric site on an enzyme earlier in the pathway.
- Binding of the end-product changes the shape of the active site of that enzyme, reducing its activity / preventing substrate binding.
- This negative feedback mechanism stops further production of the end-product when it is already at sufficient concentration, preventing waste of resources / overproduction.
Key terms in this question
metabolic pathway · end-product inhibition
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Enzymes and metabolism questions
- Explain how the structure of an enzyme's active site determines its specificity …
- Explain how competitive inhibitors affect enzyme activity, including the effect …
- Explain how the concentration of an enzyme affects the rate of an enzyme-catalys…
- Explain how pH affects the rate of an enzyme-catalysed reaction.
- Explain how substrate concentration affects the rate of an enzyme-catalysed reac…
- Explain how enzymes lower the activation energy of a reaction, and outline why t…