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← Theoretical 1

Q4 — Enzyme Inhibition — Substrate Concentration vs Rate Curves

Theoretical 1 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Enzyme Kinetics & Regulation

The following curves show the effect of substrate concentration on the rate of an enzymatic reaction: Section 1/2 trace the reaction with no inhibitor present (a linear rise, section 1, that plateaus at section 2); Section 3 traces the reaction in the presence of inhibitor X; Section 4 traces the reaction in the presence of inhibitor Y.

Rate of reaction vs. substrate concentration, with sections 1–4 marking different parts of the uninhibited and inhibited curves. Rate of reaction vs. substrate concentration. Section 1: the linear, substrate-limited rise of the uninhibited reaction. Section 2: where the uninhibited reaction plateaus at Vmax. Section 3 (dashed): the inhibitor-X curve, which converges on the same plateau as sections 1–2 at high substrate concentration. Section 4 (dash-dot): the inhibitor-Y curve, which plateaus lower and never converges with the uninhibited curve.

Choose whether the following statements about Sections 1, 2, 3, and 4 of the enzymatic reactions are true or false:

A. Section 1 is limited by (or depends on) enzyme concentration.
B. Section 2 is limited by enzyme concentration.
C. Section 3 is limited by a competitive inhibitor.
D. Section 4 is limited by an uncompetitive inhibitor.
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Question reproduced from IBO 2022, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)