Enzyme kinetics: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Enzyme kinetics

Sample item

Which kinetic change is expected with a pure noncompetitive inhibitor?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Lower Vmax with unchanged Km

A pure noncompetitive inhibitor reduces the effective amount of active enzyme, lowering Vmax without altering substrate affinity, so adding more substrate cannot fully restore maximal reaction velocity.

Option by option

  • A. Lower Vmax with unchanged Km (correct)

    Correct: pure noncompetitive inhibition lowers Vmax while Km stays unchanged.

  • B. Higher Km with unchanged Vmax

    Higher Km with preserved Vmax is typical of competitive inhibition.

  • C. Higher Vmax with lower Km

    Increasing Vmax is not the expected effect of inhibition.

  • D. No effect at any inhibitor concentration

    A true inhibitor has a measurable kinetic effect.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, Lower Vmax with unchanged Km. A pure noncompetitive inhibitor reduces the effective amount of active enzyme, lowering Vmax without altering substrate affinity, so adding more substrate cannot fully restore maximal reaction velocity.

Why is "Higher Km with unchanged Vmax" not the answer?

Higher Km with preserved Vmax is typical of competitive inhibition.

Why is "Higher Vmax with lower Km" not the answer?

Increasing Vmax is not the expected effect of inhibition.

Why is "No effect at any inhibitor concentration" not the answer?

A true inhibitor has a measurable kinetic effect.

What concept does this question test?

It tests Enzyme kinetics in Biochemistry. The correct option holds because: Correct: pure noncompetitive inhibition lowers Vmax while Km stays unchanged.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Enzyme kinetics?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.