Enzymes: 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 · Enzymes

Sample item

What does the Km of an enzyme-substrate reaction represent?

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

The answer and the reasoning

D. Substrate concentration at half maximal velocity

Km is the substrate concentration producing half of maximal velocity. A lower Km can indicate greater apparent enzyme affinity for substrate under the stated conditions.

Option by option

  • A. Maximum reaction velocity

    Vmax is the plateau velocity reached at enzyme saturation.

  • B. Substrate concentration needed to saturate every active site

    Full active-site saturation is approached at high substrate, not defined by Km.

  • C. Energy released by ATP hydrolysis

    ATP hydrolysis energy is unrelated to the Michaelis constant.

  • D. Substrate concentration at half maximal velocity (correct)

    Correct: the reaction is at half Vmax when substrate equals Km.

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 D, Substrate concentration at half maximal velocity. Km is the substrate concentration producing half of maximal velocity.

Why is "Maximum reaction velocity" not the answer?

Vmax is the plateau velocity reached at enzyme saturation.

Why is "Substrate concentration needed to saturate every active site" not the answer?

Full active-site saturation is approached at high substrate, not defined by Km.

Why is "Energy released by ATP hydrolysis" not the answer?

ATP hydrolysis energy is unrelated to the Michaelis constant.

What concept does this question test?

It tests Enzymes in Biochemistry. A lower Km can indicate greater apparent enzyme affinity for substrate under the stated conditions.

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 Enzymes?

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.