Carbohydrate metabolism: AMP and muscle glycogen phosphorylase b: 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.

Try it

Biochemistry · Carbohydrate metabolism: AMP and muscle glycogen phosphorylase b

Sample item

In a sprinting muscle, the less phosphorylated, 'b' form of glycogen phosphorylase can still be driven to break down glycogen. Which allosteric effector activates it?

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

The answer and the reasoning

A. AMP

Muscle phosphorylase b is activated allosterically by AMP, which rises when ATP is used rapidly, and is inhibited by ATP and glucose-6-phosphate. Calcium also activates phosphorylase kinase during contraction, which converts phosphorylase b to the active a form.

Option by option

  • A. AMP (correct)

    Correct. AMP signals low energy and activates phosphorylase b even without covalent modification.

  • B. ATP

    ATP inhibits phosphorylase b, since plentiful ATP means glycogen breakdown is not needed.

  • C. Insulin

    Insulin is a hormone that promotes glycogen synthesis and does not allosterically activate phosphorylase.

  • D. Glucose-6-phosphate

    Glucose-6-phosphate also inhibits phosphorylase b and acts as a signal of adequate glycolytic supply.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, AMP. Muscle phosphorylase b is activated allosterically by AMP, which rises when ATP is used rapidly, and is inhibited by ATP and glucose-6-phosphate.

Why is "ATP" not the answer?

ATP inhibits phosphorylase b, since plentiful ATP means glycogen breakdown is not needed.

Why is "Insulin" not the answer?

Insulin is a hormone that promotes glycogen synthesis and does not allosterically activate phosphorylase.

Why is "Glucose-6-phosphate" not the answer?

Glucose-6-phosphate also inhibits phosphorylase b and acts as a signal of adequate glycolytic supply.

What concept does this question test?

It tests Carbohydrate metabolism: AMP and muscle glycogen phosphorylase b in Biochemistry. Calcium also activates phosphorylase kinase during contraction, which converts phosphorylase b to the active a form.

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: AMP and muscle glycogen phosphorylase b?

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.