Biomolecules and enzymes: dynein defect in primary ciliary dyskinesia: 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 · Biomolecules and enzymes: dynein defect in primary ciliary dyskinesia

Sample item

A young man has chronic sinusitis, recurrent bronchiectasis, dextrocardia and infertility because his sperm are immotile. Electron microscopy of his cilia is most likely to show absence of which structure?

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

The answer and the reasoning

D. Dynein arms on the outer microtubule doublets

Kartagener syndrome is a form of primary ciliary dyskinesia in which the dynein arms of the axoneme are defective. Ciliary and sperm tail movement need ATP-driven sliding of the microtubule doublets by dynein. Immotile cilia fail to clear mucus and fail to establish normal left-right asymmetry in the embryo.

Option by option

  • A. Kinesin light chains in the basal body

    Kinesin carries cargo along microtubules and is not the axonemal motor of the cilium.

  • B. Keratin filaments in the ciliary shaft

    Keratin filaments are epithelial intermediate filaments and do not power ciliary beating.

  • C. Actin filaments in the ciliary core

    Actin filaments are not the motor of the ciliary axoneme.

  • D. Dynein arms on the outer microtubule doublets (correct)

    Correct. Dynein arms drive microtubule sliding, and their absence causes immotile cilia and sperm with situs inversus.

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, Dynein arms on the outer microtubule doublets. Kartagener syndrome is a form of primary ciliary dyskinesia in which the dynein arms of the axoneme are defective.

Why is "Kinesin light chains in the basal body" not the answer?

Kinesin carries cargo along microtubules and is not the axonemal motor of the cilium.

Why is "Keratin filaments in the ciliary shaft" not the answer?

Keratin filaments are epithelial intermediate filaments and do not power ciliary beating.

Why is "Actin filaments in the ciliary core" not the answer?

Actin filaments are not the motor of the ciliary axoneme.

What concept does this question test?

It tests Biomolecules and enzymes: dynein defect in primary ciliary dyskinesia in Biochemistry. Ciliary and sperm tail movement need ATP-driven sliding of the microtubule doublets by dynein. Immotile cilia fail to clear mucus and fail to establish normal left-right asymmetry in the embryo.

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 Biomolecules and enzymes: dynein defect in primary ciliary dyskinesia?

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.