Vitamins and minerals: beta-carotene cleavage: 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 · Vitamins and minerals: beta-carotene cleavage

Sample item

Beta-carotene is the most efficient provitamin A carotenoid. What happens to it in the intestinal mucosa?

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

The answer and the reasoning

D. It is cleaved centrally by a dioxygenase to yield two molecules of retinal

Beta-carotene 15,15'-dioxygenase cleaves the molecule at its centre to give two retinal molecules, which are reduced to retinol and esterified. In practice, the yield is lower than the theoretical two molecules. Carotenoids with one beta-ionone ring yield only one retinal.

Option by option

  • A. It is transaminated to retinoic acid precursors

    Beta-carotene is not transaminated; cleavage and reduction produce retinol.

  • B. It is hydroxylated by a monooxygenase to calcitriol

    Hydroxylation to calcitriol is the pathway of vitamin D, not of carotenoids.

  • C. It is carboxylated to form osteocalcin-like proteins

    Carboxylation of proteins requires vitamin K and has no link to carotenoids.

  • D. It is cleaved centrally by a dioxygenase to yield two molecules of retinal (correct)

    Correct. Central cleavage by a dioxygenase gives two retinal molecules.

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 D, It is cleaved centrally by a dioxygenase to yield two molecules of retinal. Beta-carotene 15,15'-dioxygenase cleaves the molecule at its centre to give two retinal molecules, which are reduced to retinol and esterified.

Why is "It is transaminated to retinoic acid precursors" not the answer?

Beta-carotene is not transaminated; cleavage and reduction produce retinol.

Why is "It is hydroxylated by a monooxygenase to calcitriol" not the answer?

Hydroxylation to calcitriol is the pathway of vitamin D, not of carotenoids.

Why is "It is carboxylated to form osteocalcin-like proteins" not the answer?

Carboxylation of proteins requires vitamin K and has no link to carotenoids.

What concept does this question test?

It tests Vitamins and minerals: beta-carotene cleavage in Biochemistry. In practice, the yield is lower than the theoretical two molecules. Carotenoids with one beta-ionone ring yield only one retinal.

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 Vitamins and minerals: beta-carotene cleavage?

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.