| Date | November 2011 | Marks available | 3 | Reference code | 11N.3.SL.TZ0.9 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Explain | Question number | 9 | Adapted from | N/A |
Question
Explain the control of metabolic pathways by end-product inhibition.
Markscheme
metabolic pathway is a series of enzyme-catalysed reactions;
end-product acts as inhibitor of enzyme at beginning of pathway;
allosteric site for inhibitor to bind / allosteric enzyme with two different binding sites;
more inhibition if end-product concentration rises;
prevents an excess of production/build-up of intermediate products;
Examiners report
Control of metabolic pathways by end-product inhibition was weakly done. Many were able to get one mark for stating that the end-product inhibited an enzyme at the beginning of the pathway and some got a second mark for indicating that there was an allosteric site for the inhibitor to bind with but very few got a third marking point.
