| Date | May 2018 | Marks available | 2 | Reference code | 18M.3.hl.TZ1.9 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | 9 | Adapted from | N/A |
Question
An inhibitor reduces the rate, V, of an enzyme-catalysed reaction.
Explain with reference to the binding site on the enzyme how a non-competitive inhibitor lowers the value of Vmax.
Outline the significance of the value of the Michaelis constant, Km.
Markscheme
binds at allosteric site
OR
binds away from active site
changes shape of active site
OR
renders active sites ineffective
[2 marks]
Km is inverse measure of affinity of enzyme for a substrate
OR
Km is inversely proportional to enzyme activity
OR
high value of Km indicates higher substrate concentration needed for enzyme saturation
OR
low value of Km means reaction is fast at low substrate concentration
Idea of inverse relationship must be conveyed.
Accept “high value of Km indicates low affinity of enzyme for substrate/less stable ES complex/lower enzyme activity”.
Accept “low value of Km indicates high affinity of enzyme for substrate/stable ES complex/greater enzyme activity”.
[1 mark]
