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

What happens to the apparent Km of an enzyme when a reversible competitive inhibitor is added?

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

The answer and the reasoning

C. It increases

A competitive inhibitor competes with substrate at the active site, so a higher substrate concentration is needed to reach half-maximal velocity; this increases apparent Km while Vmax can still be reached.

Option by option

  • A. It makes the enzyme irreversible

    Competitive binding is reversible in the usual kinetic model.

  • B. It decreases to zero

    Km does not fall to zero with competitive inhibition.

  • C. It increases (correct)

    Correct: competitive inhibition raises apparent Km.

  • D. It remains unchanged with lower Vmax

    Unchanged Km with reduced Vmax describes a noncompetitive pattern more closely.

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 C, It increases. A competitive inhibitor competes with substrate at the active site, so a higher substrate concentration is needed to reach half-maximal velocity; this increases apparent Km while Vmax can still be reached.

Why is "It makes the enzyme irreversible" not the answer?

Competitive binding is reversible in the usual kinetic model.

Why is "It decreases to zero" not the answer?

Km does not fall to zero with competitive inhibition.

Why is "It remains unchanged with lower Vmax" not the answer?

Unchanged Km with reduced Vmax describes a noncompetitive pattern more closely.

What concept does this question test?

It tests Enzyme kinetics in Biochemistry. The correct option holds because: Correct: competitive inhibition raises apparent Km.

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.