Cholesterol metabolism: HMG-CoA reductase: 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.

Try it

Biochemistry · Cholesterol metabolism: HMG-CoA reductase

Sample item

In a sterol-depleted hepatocyte, SREBP-2 travels to the Golgi, is cleaved, and enters the nucleus. Transcription of the LDL receptor gene rises, along with that of which rate-limiting enzyme of cholesterol synthesis?

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

The answer and the reasoning

D. HMG-CoA reductase

SREBP-2 is the sterol-responsive transcription factor and upregulates both LDL receptor uptake and cholesterol synthesis genes, chiefly the rate-limiting enzyme. Statins use this loop, because lower sterol content triggers SREBP-2 and more LDL receptors. ACAT is not induced because there is no cholesterol excess to store.

Option by option

  • A. Acyl-CoA cholesterol acyltransferase

    Cholesterol esterification would be reduced, not induced, when sterol content is low.

  • B. Lanosterol synthase

    Lanosterol synthase is not the rate-limiting enzyme of the pathway.

  • C. Squalene epoxidase

    Squalene epoxidase is a late enzyme and is not the principal SREBP-2 target for flux control.

  • D. HMG-CoA reductase (correct)

    Correct. SREBP-2 raises transcription of this rate-limiting enzyme together with the LDL receptor.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, HMG-CoA reductase. SREBP-2 is the sterol-responsive transcription factor and upregulates both LDL receptor uptake and cholesterol synthesis genes, chiefly the rate-limiting enzyme.

Why is "Acyl-CoA cholesterol acyltransferase" not the answer?

Cholesterol esterification would be reduced, not induced, when sterol content is low.

Why is "Lanosterol synthase" not the answer?

Lanosterol synthase is not the rate-limiting enzyme of the pathway.

Why is "Squalene epoxidase" not the answer?

Squalene epoxidase is a late enzyme and is not the principal SREBP-2 target for flux control.

What concept does this question test?

It tests Cholesterol metabolism: HMG-CoA reductase in Biochemistry. Statins use this loop, because lower sterol content triggers SREBP-2 and more LDL receptors. ACAT is not induced because there is no cholesterol excess to store.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Cholesterol metabolism: HMG-CoA reductase?

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.