Lipoproteins: LCAT and reverse cholesterol transport: 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 · Lipoproteins: LCAT and reverse cholesterol transport

Sample item

A 35-year-old man has corneal clouding, normocytic anaemia with target cells, proteinuria and a very low HDL cholesterol. The enzyme deficient in this condition performs which reaction?

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

The answer and the reasoning

B. Transfer of a fatty acid from phosphatidylcholine to free cholesterol on HDL, forming cholesteryl ester

Lecithin-cholesterol acyltransferase is activated by apoA-I on HDL. It esterifies free cholesterol, trapping it in the HDL core and keeping a gradient for cholesterol efflux from cells. Deficiency causes free cholesterol and lecithin to accumulate in the cornea, red cells and kidney.

Option by option

  • A. Transfer of cholesteryl ester from HDL to VLDL in exchange for triglyceride

    Cholesteryl ester exchange with triglyceride is the role of cholesteryl ester transfer protein.

  • B. Transfer of a fatty acid from phosphatidylcholine to free cholesterol on HDL, forming cholesteryl ester (correct)

    This is the LCAT reaction, whose absence leaves free cholesterol to deposit in tissues.

  • C. Hydrolysis of triglyceride in chylomicrons and VLDL at the capillary endothelium

    Triglyceride hydrolysis in lipoproteins is the role of lipoprotein lipase.

  • D. Synthesis of mevalonate from HMG-CoA in the hepatocyte

    Mevalonate formation is the HMG-CoA reductase step 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.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Transfer of a fatty acid from phosphatidylcholine to free cholesterol on HDL, forming cholesteryl ester. Lecithin-cholesterol acyltransferase is activated by apoA-I on HDL.

Why is "Transfer of cholesteryl ester from HDL to VLDL in exchange for trigly…" not the answer?

Cholesteryl ester exchange with triglyceride is the role of cholesteryl ester transfer protein.

Why is "Hydrolysis of triglyceride in chylomicrons and VLDL at the capillary…" not the answer?

Triglyceride hydrolysis in lipoproteins is the role of lipoprotein lipase.

Why is "Synthesis of mevalonate from HMG-CoA in the hepatocyte" not the answer?

Mevalonate formation is the HMG-CoA reductase step of cholesterol synthesis.

What concept does this question test?

It tests Lipoproteins: LCAT and reverse cholesterol transport in Biochemistry. It esterifies free cholesterol, trapping it in the HDL core and keeping a gradient for cholesterol efflux from cells. Deficiency causes free cholesterol and lecithin to accumulate in the cornea, red cells and kidney.

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 Lipoproteins: LCAT and reverse cholesterol transport?

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.