Carbohydrate metabolism: glucose sensing by the pancreatic beta cell: 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: glucose sensing by the pancreatic beta cell

Sample item

After a meal, glucose enters beta cells and is phosphorylated. Insulin secretion then follows a sequence of events. Which step comes directly before the opening of voltage-gated calcium channels?

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

The answer and the reasoning

C. Closure of ATP-sensitive potassium channels with membrane depolarisation

Metabolism of glucose raises the ATP to ADP ratio, which closes ATP-sensitive potassium channels. The membrane depolarises, voltage-gated calcium channels open and calcium triggers exocytosis of insulin granules. Sulfonylureas act by closing the same channel.

Option by option

  • A. Activation of glycogen phosphorylase by cyclic AMP

    Glycogen phosphorylase activation by cyclic AMP is a hepatic response to glucagon and not part of this pathway.

  • B. Opening of ATP-sensitive potassium channels with hyperpolarisation

    Channel opening would hyperpolarise the cell and prevent calcium entry, as happens with diazoxide.

  • C. Closure of ATP-sensitive potassium channels with membrane depolarisation (correct)

    Correct. A rising ATP to ADP ratio closes the potassium channel and depolarises the cell.

  • D. Binding of insulin to its receptor on the beta cell

    Insulin binding to its own receptor is not the trigger for calcium channel opening in the beta cell.

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, Closure of ATP-sensitive potassium channels with membrane depolarisation. Metabolism of glucose raises the ATP to ADP ratio, which closes ATP-sensitive potassium channels.

Why is "Activation of glycogen phosphorylase by cyclic AMP" not the answer?

Glycogen phosphorylase activation by cyclic AMP is a hepatic response to glucagon and not part of this pathway.

Why is "Opening of ATP-sensitive potassium channels with hyperpolarisation" not the answer?

Channel opening would hyperpolarise the cell and prevent calcium entry, as happens with diazoxide.

Why is "Binding of insulin to its receptor on the beta cell" not the answer?

Insulin binding to its own receptor is not the trigger for calcium channel opening in the beta cell.

What concept does this question test?

It tests Carbohydrate metabolism: glucose sensing by the pancreatic beta cell in Biochemistry. The membrane depolarises, voltage-gated calcium channels open and calcium triggers exocytosis of insulin granules. Sulfonylureas act by closing the same channel.

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: glucose sensing by the pancreatic beta cell?

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.