Nucleotide metabolism: dihydroorotate dehydrogenase location: 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 · Nucleotide metabolism: dihydroorotate dehydrogenase location

Sample item

Which de novo pyrimidine synthetic enzyme is located on the inner mitochondrial membrane and passes electrons to ubiquinone?

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

The answer and the reasoning

A. Dihydroorotate dehydrogenase

Dihydroorotate dehydrogenase oxidises dihydroorotate to orotate and links the reaction to the respiratory chain through ubiquinone. All the other de novo pyrimidine enzymes are cytosolic.

Option by option

  • A. Dihydroorotate dehydrogenase (correct)

    Correct. This is the only mitochondrial membrane enzyme of the pathway.

  • B. Thymidylate synthase

    This enzyme is cytosolic and forms thymidylate from dUMP.

  • C. Aspartate transcarbamoylase

    This enzyme is part of the cytosolic CAD protein.

  • D. OMP decarboxylase

    This enzyme is part of cytosolic UMP synthase.

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 A, Dihydroorotate dehydrogenase. Dihydroorotate dehydrogenase oxidises dihydroorotate to orotate and links the reaction to the respiratory chain through ubiquinone.

Why is "Thymidylate synthase" not the answer?

This enzyme is cytosolic and forms thymidylate from dUMP.

Why is "Aspartate transcarbamoylase" not the answer?

This enzyme is part of the cytosolic CAD protein.

Why is "OMP decarboxylase" not the answer?

This enzyme is part of cytosolic UMP synthase.

What concept does this question test?

It tests Nucleotide metabolism: dihydroorotate dehydrogenase location in Biochemistry. All the other de novo pyrimidine enzymes are cytosolic.

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 Nucleotide metabolism: dihydroorotate dehydrogenase location?

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.