A Levels Biology (9700)•9700/12/M/J/24
Explanation
Competitive Inhibition in Enzyme Kinetics
Steps:
- Competitive inhibitors bind to the enzyme's active site, competing with substrate.
- V_max remains unchanged because high substrate concentrations displace the inhibitor, allowing maximum velocity.
- K_m increases as more substrate is needed to achieve half V_max due to reduced effective enzyme availability.
- Option A matches: no change in V_max, increase in K_m.
Why A is correct:
- In the Michaelis-Menten equation, competitive inhibition modifies K_m to K_m(1 + [I]/K_i) while V_max stays constant, per enzyme kinetics principles.
Why the others are wrong:
- B: K_m changes, so incorrect for competitive inhibition.
- C: V_max does not decrease; that's non-competitive.
- D: V_max does not decrease; Km alone changes.
Final answer: A
Topic: Factors that affect enzyme action
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