Protein biochemistry: 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 · Protein biochemistry

Sample item

What does an enzyme's Km represent in the standard Michaelis-Menten model?

AEnergy released by ATP hydrolysisBSubstrate concentration at half maximal velocityCNumber of peptide bonds in the enzymeDMaximum enzyme concentration in plasma

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

The answer and the reasoning

B. Substrate concentration at half maximal velocity

Km is the substrate concentration at which reaction velocity is half of Vmax in the Michaelis-Menten model; it is often used as a practical indicator of substrate affinity under defined conditions.

Option by option

A. Energy released by ATP hydrolysis
ATP hydrolysis energy is a thermodynamic quantity, not Km.
B. Substrate concentration at half maximal velocity (correct)
Correct: Km corresponds to half-maximal reaction velocity.
C. Number of peptide bonds in the enzyme
Protein length does not define Km.
D. Maximum enzyme concentration in plasma
Km is not a measure of plasma enzyme amount.

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.

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Substrate concentration at half maximal velocity. Km is the substrate concentration at which reaction velocity is half of Vmax in the Michaelis-Menten model; it is often used as a practical indicator of substrate affinity under defined conditions.

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

ATP hydrolysis energy is a thermodynamic quantity, not Km.

Why is "Number of peptide bonds in the enzyme" not the answer?

Protein length does not define Km.

Why is "Maximum enzyme concentration in plasma" not the answer?

Km is not a measure of plasma enzyme amount.

What concept does this question test?

It tests Protein biochemistry in Biochemistry. The correct option holds because: Correct: Km corresponds to half-maximal reaction velocity.

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 Protein biochemistry?

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.