Lipid metabolism: glycerol-3-phosphate in adipose tissue: 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: glycerol-3-phosphate in adipose tissue

Sample item

Adipocytes lack glycerol kinase. In the fed state, from where does the glycerol-3-phosphate needed to esterify fatty acids come?

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

The answer and the reasoning

D. Reduction of dihydroxyacetone phosphate from glycolysis

Without glycerol kinase, adipose tissue relies on glucose uptake to supply dihydroxyacetone phosphate, which glycerol-3-phosphate dehydrogenase reduces to glycerol-3-phosphate. In fasting, little glucose enters, so released fatty acids are exported rather than re-esterified, and glycerol travels to the liver.

Option by option

  • A. Transamination of phosphoenolpyruvate

    Phosphoenolpyruvate is a glycolytic intermediate and is not converted to glycerol-3-phosphate by transamination.

  • B. Oxidation of glycerol by glycerol dehydrogenase

    No glycerol dehydrogenase step in adipose tissue provides glycerol-3-phosphate for esterification.

  • C. Phosphorylation of free glycerol released from VLDL

    Free glycerol cannot be phosphorylated in adipose tissue since glycerol kinase is absent.

  • D. Reduction of dihydroxyacetone phosphate from glycolysis (correct)

    Correct. DHAP from glycolysis is reduced to glycerol-3-phosphate when glucose is available.

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 D, Reduction of dihydroxyacetone phosphate from glycolysis. Without glycerol kinase, adipose tissue relies on glucose uptake to supply dihydroxyacetone phosphate, which glycerol-3-phosphate dehydrogenase reduces to glycerol-3-phosphate.

Why is "Transamination of phosphoenolpyruvate" not the answer?

Phosphoenolpyruvate is a glycolytic intermediate and is not converted to glycerol-3-phosphate by transamination.

Why is "Oxidation of glycerol by glycerol dehydrogenase" not the answer?

No glycerol dehydrogenase step in adipose tissue provides glycerol-3-phosphate for esterification.

Why is "Phosphorylation of free glycerol released from VLDL" not the answer?

Free glycerol cannot be phosphorylated in adipose tissue since glycerol kinase is absent.

What concept does this question test?

It tests Lipid metabolism: glycerol-3-phosphate in adipose tissue in Biochemistry. In fasting, little glucose enters, so released fatty acids are exported rather than re-esterified, and glycerol travels to the liver.

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 Lipid metabolism: glycerol-3-phosphate in adipose tissue?

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.