General physiology: non-shivering thermogenesis: practice question

A Physiology 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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Physiology · General physiology: non-shivering thermogenesis

Sample item

A healthy full-term newborn kept in a cool room maintains core temperature without shivering. Which process in brown adipose tissue accounts for the heat produced?

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

The answer and the reasoning

C. Proton leak through uncoupling protein 1, which uncouples oxidation from ATP synthesis

Brown fat is rich in mitochondria that carry uncoupling protein 1 (thermogenin). The protein lets protons re-enter the matrix without passing through ATP synthase, so the energy of fuel oxidation is released as heat. It is stimulated by sympathetic noradrenaline acting on beta-3 receptors and is the main non-shivering heat source in the newborn.

Option by option

  • A. Futile calcium cycling by the sarcoplasmic reticulum of skeletal muscle

    Calcium cycling in skeletal muscle is a separate form of non-shivering heat production and is not the brown-fat mechanism.

  • B. Increased ATP hydrolysis by the Na-K ATPase of white adipocytes

    White adipocytes store fat and are not a major source of heat.

  • C. Proton leak through uncoupling protein 1, which uncouples oxidation from ATP synthesis (correct)

    Correct. UCP1 dissipates the proton gradient as heat instead of making ATP.

  • D. Heat released during glycogen synthesis in the neonatal liver

    Glycogen synthesis consumes energy and does not generate a large heat output that protects the newborn.

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 Physiology question

What is the answer to this Physiology question?

The best answer is C, Proton leak through uncoupling protein 1, which uncouples oxidation from ATP synthesis. Brown fat is rich in mitochondria that carry uncoupling protein 1 (thermogenin).

Why is "Futile calcium cycling by the sarcoplasmic reticulum of skeletal musc…" not the answer?

Calcium cycling in skeletal muscle is a separate form of non-shivering heat production and is not the brown-fat mechanism.

Why is "Increased ATP hydrolysis by the Na-K ATPase of white adipocytes" not the answer?

White adipocytes store fat and are not a major source of heat.

Why is "Heat released during glycogen synthesis in the neonatal liver" not the answer?

Glycogen synthesis consumes energy and does not generate a large heat output that protects the newborn.

What concept does this question test?

It tests General physiology: non-shivering thermogenesis in Physiology. The protein lets protons re-enter the matrix without passing through ATP synthase, so the energy of fuel oxidation is released as heat. It is stimulated by sympathetic noradrenaline acting on beta-3 receptors and is the main non-shivering heat source in the newborn.

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 General physiology: non-shivering thermogenesis?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.