Vitamins: biotin deficiency: 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: biotin deficiency

Sample item

A bodybuilder who eats about a dozen raw egg whites daily develops scaly dermatitis, hair thinning, lethargy and muscle pain. Which reaction is impaired?

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

The answer and the reasoning

C. Pyruvate to oxaloacetate

Avidin in raw egg white binds biotin tightly and prevents its absorption. Biotin is the cofactor of carboxylases, including pyruvate carboxylase, acetyl-CoA carboxylase, propionyl-CoA carboxylase and methylcrotonyl-CoA carboxylase. Impaired pyruvate carboxylation reduces gluconeogenesis and oxaloacetate supply.

Option by option

  • A. Pyruvate to acetyl-CoA

    Conversion to acetyl-CoA uses the PDH complex, which needs thiamine, lipoate, FAD, NAD and CoA, not biotin.

  • B. Pyruvate to lactate

    Lactate dehydrogenase needs NADH and is unaffected by biotin status.

  • C. Pyruvate to oxaloacetate (correct)

    Pyruvate carboxylase is biotin dependent, so avidin-induced deficiency blocks this carboxylation.

  • D. Oxaloacetate to phosphoenolpyruvate

    PEP carboxykinase needs GTP and a divalent cation, not biotin.

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, Pyruvate to oxaloacetate. Avidin in raw egg white binds biotin tightly and prevents its absorption.

Why is "Pyruvate to acetyl-CoA" not the answer?

Conversion to acetyl-CoA uses the PDH complex, which needs thiamine, lipoate, FAD, NAD and CoA, not biotin.

Why is "Pyruvate to lactate" not the answer?

Lactate dehydrogenase needs NADH and is unaffected by biotin status.

Why is "Oxaloacetate to phosphoenolpyruvate" not the answer?

PEP carboxykinase needs GTP and a divalent cation, not biotin.

What concept does this question test?

It tests Vitamins: biotin deficiency in Biochemistry. Biotin is the cofactor of carboxylases, including pyruvate carboxylase, acetyl-CoA carboxylase, propionyl-CoA carboxylase and methylcrotonyl-CoA carboxylase. Impaired pyruvate carboxylation reduces gluconeogenesis and oxaloacetate supply.

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: biotin deficiency?

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.