Lipid metabolism: glucocorticoids and phospholipase A2: 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: glucocorticoids and phospholipase A2

Sample item

Glucocorticoids reduce production of both prostaglandins and leukotrienes by inducing annexin-1 (lipocortin). Which enzyme does this protein inhibit?

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

The answer and the reasoning

C. Phospholipase A2

Phospholipase A2 releases arachidonic acid from membrane phospholipid, the common substrate for cyclooxygenase and lipoxygenase pathways. Blocking its activity lowers all eicosanoids, which explains the broad anti-inflammatory action of steroids compared with NSAIDs.

Option by option

  • A. Phospholipase C

    Phospholipase C generates IP3 and diacylglycerol and is not the target of annexin-1.

  • B. Cyclooxygenase

    Cyclooxygenase is inhibited directly by NSAIDs, and this would not reduce leukotrienes.

  • C. Phospholipase A2 (correct)

    Correct. Annexin-1 inhibits phospholipase A2 and so cuts arachidonate supply for both pathways.

  • D. 5-Lipoxygenase

    5-Lipoxygenase inhibition, as with zileuton, would lower leukotrienes but not prostaglandins.

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, Phospholipase A2. Phospholipase A2 releases arachidonic acid from membrane phospholipid, the common substrate for cyclooxygenase and lipoxygenase pathways.

Why is "Phospholipase C" not the answer?

Phospholipase C generates IP3 and diacylglycerol and is not the target of annexin-1.

Why is "Cyclooxygenase" not the answer?

Cyclooxygenase is inhibited directly by NSAIDs, and this would not reduce leukotrienes.

Why is "5-Lipoxygenase" not the answer?

5-Lipoxygenase inhibition, as with zileuton, would lower leukotrienes but not prostaglandins.

What concept does this question test?

It tests Lipid metabolism: glucocorticoids and phospholipase A2 in Biochemistry. Blocking its activity lowers all eicosanoids, which explains the broad anti-inflammatory action of steroids compared with NSAIDs.

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: glucocorticoids and phospholipase A2?

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.