| Date | May 2015 | Marks available | 3 | Reference code | 15M.3.SL.TZ1.9 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 9 | Adapted from | N/A |
Question
The enzyme hexokinase catalyses the reaction between glucose and ATP to form Glucose –6– phosphate and ADP.
The activity of hexokinase is regulated by end product inhibition. Explain how a reaction can be controlled by end product inhibition.
Markscheme
a. metabolic pathway is a series of enzyme catalysed reactions;
b. allosteric enzyme catalyses one step/first step in the mechanism/chain of reactions;
c. enzyme is inhibited by the end product;
d. end product binds at a site other than the active site/allosteric site;
e. reaction mechanism is interrupted / product formation stops;
f. more inhibition of enzyme as end product concentration rises / less inhibition as end product reduces;
g. example of negative feedback;
Examiners report
There was better knowledge of end product inhibition but again candidates found their explanations hard to express.
