Lipid metabolism: ACAT and intracellular cholesterol esterification: 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 · Lipid metabolism: ACAT and intracellular cholesterol esterification

Sample item

When free cholesterol builds up inside a cell, an endoplasmic reticulum enzyme esterifies it with a fatty acyl group for storage in droplets. Which enzyme is this?

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

The answer and the reasoning

C. Acyl-CoA cholesterol acyltransferase

ACAT (also called SOAT) transfers a fatty acid from acyl-CoA to cholesterol inside cells, producing cholesteryl esters for storage or for packaging into lipoproteins. LCAT, by contrast, acts in plasma on HDL using lecithin as the acyl donor.

Option by option

  • A. Cholesteryl ester transfer protein

    CETP is a plasma transfer protein exchanging cholesteryl esters and triglyceride and is not an esterifying enzyme.

  • B. Hormone-sensitive lipase

    Hormone-sensitive lipase hydrolyses cholesteryl esters and triglyceride, doing the reverse reaction.

  • C. Acyl-CoA cholesterol acyltransferase (correct)

    Correct. ACAT esterifies free cholesterol within cells using acyl-CoA.

  • D. Lecithin-cholesterol acyltransferase

    LCAT esterifies cholesterol in plasma on HDL and is activated by apoA-I.

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, Acyl-CoA cholesterol acyltransferase. ACAT (also called SOAT) transfers a fatty acid from acyl-CoA to cholesterol inside cells, producing cholesteryl esters for storage or for packaging into lipoproteins.

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

CETP is a plasma transfer protein exchanging cholesteryl esters and triglyceride and is not an esterifying enzyme.

Why is "Hormone-sensitive lipase" not the answer?

Hormone-sensitive lipase hydrolyses cholesteryl esters and triglyceride, doing the reverse reaction.

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

LCAT esterifies cholesterol in plasma on HDL and is activated by apoA-I.

What concept does this question test?

It tests Lipid metabolism: ACAT and intracellular cholesterol esterification in Biochemistry. LCAT, by contrast, acts in plasma on HDL using lecithin as the acyl donor.

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 Lipid metabolism: ACAT and intracellular cholesterol esterification?

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.