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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.

[2]
a.

Outline the significance of the value of the Michaelis constant, Km.

[1]
b.

Markscheme

binds at allosteric site

OR

binds away from active site

 

changes shape of active site

OR

renders active sites ineffective

 

[2 marks]

a.

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]

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Options » B: Biochemistry » B.7 Proteins and enzymes (HL only)
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