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.

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Biochemistry · Cholesterol metabolism: HMG-CoA reductase

Sample item

A patient takes a red yeast rice supplement for high cholesterol. Its active component, monacolin K, is chemically identical to lovastatin. Which enzyme does it inhibit to lower LDL?

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

The answer and the reasoning

D. HMG-CoA reductase

Monacolin K is lovastatin and so competitively inhibits the rate-limiting enzyme of cholesterol synthesis, with the same benefits and the same risk of myopathy. Unregulated supplements may therefore cause statin-type adverse effects. The other options are plasma enzymes of lipoprotein metabolism, not sites of synthesis.

Option by option

  • A. Cholesterol ester transfer protein

    Cholesterol ester transfer protein exchanges lipids between lipoproteins and is not the target of this compound.

  • B. Lipoprotein lipase

    Lipoprotein lipase hydrolyses triglycerides in chylomicrons and VLDL and is not inhibited by statins.

  • C. Lecithin-cholesterol acyltransferase

    Lecithin-cholesterol acyltransferase esterifies cholesterol on HDL and is not a statin target.

  • D. HMG-CoA reductase (correct)

    Correct. Monacolin K is lovastatin and blocks the rate-limiting enzyme of cholesterol synthesis.

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. Monacolin K is lovastatin and so competitively inhibits the rate-limiting enzyme of cholesterol synthesis, with the same benefits and the same risk of myopathy.

Why is "Cholesterol ester transfer protein" not the answer?

Cholesterol ester transfer protein exchanges lipids between lipoproteins and is not the target of this compound.

Why is "Lipoprotein lipase" not the answer?

Lipoprotein lipase hydrolyses triglycerides in chylomicrons and VLDL and is not inhibited by statins.

Why is "Lecithin-cholesterol acyltransferase" not the answer?

Lecithin-cholesterol acyltransferase esterifies cholesterol on HDL and is not a statin target.

What concept does this question test?

It tests Cholesterol metabolism: HMG-CoA reductase in Biochemistry. Unregulated supplements may therefore cause statin-type adverse effects. The other options are plasma enzymes of lipoprotein metabolism, not sites of synthesis.

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 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.