Lipolysis: hormone-sensitive lipase regulation: 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 · Lipolysis: hormone-sensitive lipase regulation

Sample item

After a carbohydrate-rich meal, plasma insulin rises and lipolysis in adipose tissue falls. What is the biochemical basis?

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

The answer and the reasoning

C. Insulin lowers cAMP and promotes dephosphorylation, inactivating hormone-sensitive lipase

Catecholamines and glucagon raise cAMP and activate protein kinase A, which phosphorylates and activates hormone-sensitive lipase and perilipin. Insulin activates phosphodiesterase, lowering cAMP, and activates protein phosphatase, so the lipase is dephosphorylated and inactive. At the same time insulin increases adipose lipoprotein lipase to promote fat storage.

Option by option

  • A. Insulin phosphorylates hormone-sensitive lipase through protein kinase A

    Phosphorylation by protein kinase A activates the lipase and is driven by adrenaline, not insulin.

  • B. Insulin inhibits lipoprotein lipase on adipose capillaries

    Insulin increases, rather than inhibits, adipose lipoprotein lipase.

  • C. Insulin lowers cAMP and promotes dephosphorylation, inactivating hormone-sensitive lipase (correct)

    Reduced cAMP and dephosphorylation switch off lipolysis in the fed state.

  • D. Insulin raises cAMP and activates adenylyl cyclase in adipocytes

    Raised cAMP is the effect of adrenaline and glucagon, which stimulate lipolysis.

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, Insulin lowers cAMP and promotes dephosphorylation, inactivating hormone-sensitive lipase. Catecholamines and glucagon raise cAMP and activate protein kinase A, which phosphorylates and activates hormone-sensitive lipase and perilipin.

Why is "Insulin phosphorylates hormone-sensitive lipase through protein kinas…" not the answer?

Phosphorylation by protein kinase A activates the lipase and is driven by adrenaline, not insulin.

Why is "Insulin inhibits lipoprotein lipase on adipose capillaries" not the answer?

Insulin increases, rather than inhibits, adipose lipoprotein lipase.

Why is "Insulin raises cAMP and activates adenylyl cyclase in adipocytes" not the answer?

Raised cAMP is the effect of adrenaline and glucagon, which stimulate lipolysis.

What concept does this question test?

It tests Lipolysis: hormone-sensitive lipase regulation in Biochemistry. Insulin activates phosphodiesterase, lowering cAMP, and activates protein phosphatase, so the lipase is dephosphorylated and inactive. At the same time insulin increases adipose lipoprotein lipase to promote fat storage.

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 Lipolysis: hormone-sensitive lipase regulation?

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.