Vitamins: biotin and avidin: 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 and avidin

Sample item

A 26-year-old bodybuilder who consumes about a dozen raw egg whites daily presents with thinning hair, scaly periorificial dermatitis, conjunctivitis and depression. Which mechanism explains his deficiency state?

AOvalbumin inactivates biotin-dependent enzymes through phosphorylationBEgg-white lysozyme destroys intestinal biotin-producing flora directlyCAvidin in egg white binds biotin tightly and prevents its absorptionDRaw egg phytate chelates biotin in the lumen

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

The answer and the reasoning

C. Avidin in egg white binds biotin tightly and prevents its absorption

Avidin is a glycoprotein in raw egg white that binds biotin with extremely high affinity, forming a complex resistant to intestinal proteases. Biotin is the coenzyme of carboxylases such as pyruvate carboxylase, acetyl-CoA carboxylase and propionyl-CoA carboxylase. Cooking denatures avidin, so cooked eggs do not cause deficiency.

Option by option

A. Ovalbumin inactivates biotin-dependent enzymes through phosphorylation
Ovalbumin does not inactivate carboxylases by phosphorylation.
B. Egg-white lysozyme destroys intestinal biotin-producing flora directly
Lysozyme acts on bacterial cell walls, but this is not the established mechanism and does not describe the avidin effect.
C. Avidin in egg white binds biotin tightly and prevents its absorption (correct)
Correct. The avidin-biotin complex cannot be absorbed.
D. Raw egg phytate chelates biotin in the lumen
Phytate chelates minerals such as zinc and iron, 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.

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Avidin in egg white binds biotin tightly and prevents its absorption. Avidin is a glycoprotein in raw egg white that binds biotin with extremely high affinity, forming a complex resistant to intestinal proteases.

Why is "Ovalbumin inactivates biotin-dependent enzymes through phosphorylation" not the answer?

Ovalbumin does not inactivate carboxylases by phosphorylation.

Why is "Egg-white lysozyme destroys intestinal biotin-producing flora directly" not the answer?

Lysozyme acts on bacterial cell walls, but this is not the established mechanism and does not describe the avidin effect.

Why is "Raw egg phytate chelates biotin in the lumen" not the answer?

Phytate chelates minerals such as zinc and iron, not biotin.

What concept does this question test?

It tests Vitamins: biotin and avidin in Biochemistry. Biotin is the coenzyme of carboxylases such as pyruvate carboxylase, acetyl-CoA carboxylase and propionyl-CoA carboxylase. Cooking denatures avidin, so cooked eggs do not cause deficiency.

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 and avidin?

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.