Question 19M.2.HL.TZ1.b
| Date | May 2019 | Marks available | [Maximum mark: 5] | Reference code | 19M.2.HL.TZ1.b |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Outline | Question number | b | Adapted from | N/A |
Outline the control of metabolism by end-product inhibition.
[5]
a. metabolism is chains/web of enzyme-catalyzed reactions
OR
metabolic pathway is a chain of enzyme-catalyzed reactions ✔
b. end product/inhibitor is final product of chain/pathway ✔
c. inhibits/binds to/blocks the first enzyme in chain/pathway ✔
d. non-competitive inhibition ✔
e. end-product/inhibitor binds to an allosteric site/site away from the active site ✔
f. changes the shape of the active site/affinity of the active site «for the substrate» ✔
g. prevents intermediates from building up
OR
prevents formation of excess «end» product/stops production when there is enough
OR
whole metabolic pathway can be switched off ✔
h. negative feedback ✔
i. binding of the end product/inhibitor is reversible
OR
pathway restarts if end product/inhibitor detaches/if end product concentration is low ✔
j. isoleucine inhibits/slows «activity of first enzyme in» threonine to isoleucine pathway ✔
Allow mark points shown in clearly annotated diagrams.
To gain mpd, mpe and mpf the answer must be in the context of end-product inhibition, not enzyme inhibition generally.
Answers to this question were rather polarised. Candidates who had studied this topic and understood it had no difficulty in scoring high marks but other candidates struggled to include any useful ideas in their answers. Weaker answers tended to exclude the ideas of enzyme catalysis, pathways of reactions and the mechanisms involved in non-competitive enzyme inhibition. Diagrams to illustrate the process were a valuable part of some answers.
