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, muscle produces lactate that is later converted to glucose elsewhere. Which statement about this cycle is correct?

AThe liver converts lactate to glucose by gluconeogenesis at a net cost of ATPBThe cycle yields net ATP for the bodyCMuscle converts lactate to glucose and releases itDLactate is converted to glucose in red cells

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

The answer and the reasoning

A. The liver converts lactate to glucose by gluconeogenesis at a net cost of ATP

In the Cori cycle, lactate from muscle and red cells travels to the liver, where it is converted to pyruvate and then glucose, which returns to the peripheral tissues. Gluconeogenesis uses 6 ATP equivalents per glucose, whereas glycolysis yields 2, giving a net cost.

Option by option

A. The liver converts lactate to glucose by gluconeogenesis at a net cost of ATP (correct)
Correct. The liver pays the energy cost.
B. The cycle yields net ATP for the body
The cycle costs a net 4 ATP equivalents.
C. Muscle converts lactate to glucose and releases it
Muscle lacks glucose-6-phosphatase and cannot release free glucose.
D. Lactate is converted to glucose in red cells
Red cells lack mitochondria and produce lactate but cannot make glucose.

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.

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, The liver converts lactate to glucose by gluconeogenesis at a net cost of ATP. In the Cori cycle, lactate from muscle and red cells travels to the liver, where it is converted to pyruvate and then glucose, which returns to the peripheral tissues.

Why is "The cycle yields net ATP for the body" not the answer?

The cycle costs a net 4 ATP equivalents.

Why is "Muscle converts lactate to glucose and releases it" not the answer?

Muscle lacks glucose-6-phosphatase and cannot release free glucose.

Why is "Lactate is converted to glucose in red cells" not the answer?

Red cells lack mitochondria and produce lactate but cannot make glucose.

What concept does this question test?

It tests Carbohydrate metabolism: Cori cycle in Biochemistry. Gluconeogenesis uses 6 ATP equivalents per glucose, whereas glycolysis yields 2, giving a net cost.

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.