Carbohydrate metabolism: fructose-2,6-bisphosphate: 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: fructose-2,6-bisphosphate

Sample item

One hour after a carbohydrate-rich meal, the insulin to glucagon ratio is high. What happens in hepatocytes?

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

The answer and the reasoning

B. The bifunctional enzyme is dephosphorylated, PFK-2 activity rises, and fructose-2,6-bisphosphate activates PFK-1

In the fed state, insulin favours dephosphorylation of the bifunctional PFK-2/FBPase-2 enzyme, activating the kinase domain. Fructose-2,6-bisphosphate then rises, strongly stimulating PFK-1 and inhibiting fructose-1,6-bisphosphatase, so glycolysis proceeds and gluconeogenesis is suppressed.

Option by option

  • A. Fructose-2,6-bisphosphate falls and activates fructose-1,6-bisphosphatase

    A fall in fructose-2,6-bisphosphate would relieve inhibition of gluconeogenesis, which is the fasting pattern.

  • B. The bifunctional enzyme is dephosphorylated, PFK-2 activity rises, and fructose-2,6-bisphosphate activates PFK-1 (correct)

    Dephosphorylation activates PFK-2, and the resulting fructose-2,6-bisphosphate switches the liver towards glycolysis.

  • C. Fructose-2,6-bisphosphate rises and inhibits phosphofructokinase-1

    Fructose-2,6-bisphosphate is an activator, not an inhibitor, of PFK-1.

  • D. The bifunctional enzyme is phosphorylated, and fructose-2,6-bisphosphatase activity lowers fructose-2,6-bisphosphate

    Phosphorylation by protein kinase A occurs with glucagon in the fasting state, not after a meal.

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 B, The bifunctional enzyme is dephosphorylated, PFK-2 activity rises, and fructose-2,6-bisphosphate activates PFK-1. In the fed state, insulin favours dephosphorylation of the bifunctional PFK-2/FBPase-2 enzyme, activating the kinase domain.

Why is "Fructose-2,6-bisphosphate falls and activates fructose-1,6-bisphospha…" not the answer?

A fall in fructose-2,6-bisphosphate would relieve inhibition of gluconeogenesis, which is the fasting pattern.

Why is "Fructose-2,6-bisphosphate rises and inhibits phosphofructokinase-1" not the answer?

Fructose-2,6-bisphosphate is an activator, not an inhibitor, of PFK-1.

Why is "The bifunctional enzyme is phosphorylated, and fructose-2,6-bisphosph…" not the answer?

Phosphorylation by protein kinase A occurs with glucagon in the fasting state, not after a meal.

What concept does this question test?

It tests Carbohydrate metabolism: fructose-2,6-bisphosphate in Biochemistry. Fructose-2,6-bisphosphate then rises, strongly stimulating PFK-1 and inhibiting fructose-1,6-bisphosphatase, so glycolysis proceeds and gluconeogenesis is suppressed.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: fructose-2,6-bisphosphate?

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.