Question

Which of the following options is correct about structures visible in the cross-section of a centriole?

	Peripheral microtubules (triplets)	Central microtubules (singlets)	Hub	Spokes	Inter triplet bridge
(a)	9	2	1	9	9
(b)	9	2	9	9	9
(c)	9	2	1	2	2
(d)	9	0	1	9	9

• A. a
• B. b
• C. c
• D. d

Answer 1

Answer: (D)

A centriole possesses a whorl of nine peripheral fibrils. Fibrils are absent in the centre. The arrangement is, therefore, called $9+0$ which run parallel to one another but at an angle of $40^{\circ }$. Each fibril is made up of three sub fibres called triplet fibril. The three sub-fibres are in reality microtubules joined together by their margins and, therefore, sharing the common walls made of $2-3$ protofilaments. The centre of centriole possesses a rod-shaped proteinaceous mass known as hub. The hub has a diameter of $2.5nm$. From the hub, develops $9$ proteinaceous strands towards the peripheral triplet fibrils called radial fibres or spokes