Cilia · Histology

Which of the following describes the arrangement of microtubules in the central singlets of a motile cilium?

  1. Two complete 13-protofilament microtubules
  2. One complete and one incomplete microtubule
  3. Three triplets of 10 protofilaments each
  4. Randomly scattered dimers
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Correct answer: Two complete 13-protofilament microtubules

The central singlets (the '2' in 9+2) are two separate, complete microtubules, each composed of 13 protofilaments of alpha and beta tubulin. In contrast, the peripheral doublets consist of one complete (A) and one incomplete (B) microtubule.

Difficulty: Medium Question 17 of 20

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