Carbohydrate metabolism: Cori cycle: 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 · Carbohydrate metabolism: Cori cycle

Sample item

During a sprint, lactate leaves muscle, is converted to glucose in the liver and returns to muscle. What is the net ATP cost of this cycle?

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

The answer and the reasoning

C. 4 ATP equivalents consumed

Glucose synthesis in the liver spends about six high-energy phosphates, while glycolysis in muscle yields two ATP. The net cost is four, which is why the cycle moves the metabolic burden from muscle to liver.

Option by option

  • A. No net ATP change

    The cycle is energy-consuming, not neutral.

  • B. 2 ATP equivalents gained

    A net gain would make a futile cycle profitable, which it is not.

  • C. 4 ATP equivalents consumed (correct)

    Correct. Six are spent in the liver and two gained in muscle.

  • D. 6 ATP equivalents gained

    Six equals the cost in the liver alone and ignores the gain in muscle.

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, 4 ATP equivalents consumed. Glucose synthesis in the liver spends about six high-energy phosphates, while glycolysis in muscle yields two ATP.

Why is "No net ATP change" not the answer?

The cycle is energy-consuming, not neutral.

Why is "2 ATP equivalents gained" not the answer?

A net gain would make a futile cycle profitable, which it is not.

Why is "6 ATP equivalents gained" not the answer?

Six equals the cost in the liver alone and ignores the gain in muscle.

What concept does this question test?

It tests Carbohydrate metabolism: Cori cycle in Biochemistry. The net cost is four, which is why the cycle moves the metabolic burden from muscle to liver.

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 Carbohydrate metabolism: Cori cycle?

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.