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

Options

A. `{:("Peripheral","Central","Hub","Spokes","Inter"),("microtubules","microtubules",,,"triplet"),("(triplets)","(singlets)",,,"bridge"),(" 9"," 2"," 1"," 9"," 9"):}`
B. `{:("Peripheral","Central","Hub","Spokes","Inter"),("microtubules","microtubules",,,"triplet"),("(triplets)","(singlets)",,,"bridge"),(" 9"," 2"," 9"," 9"," 9"):}`
C. `{:("Peripheral","Central","Hub","Spokes","Inter"),("microtubules","microtubules",,,"triplet"),("(triplets)","(singlets)",,,"bridge"),(" 9"," 2"," 1"," 2"," 2"):}`
D. `{:("Peripheral","Central","Hub","Spokes","Inter"),("microtubules","microtubules",,,"triplet"),("(triplets)","(singlets)",,,"bridge"),(" 9"," 0"," 1"," 9"," 9"):}`

Answer

D

Explanation

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 an an angle of `40^(@)`. Each fibril is made up of three subfibres 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 rod-shaped proteinaceous mass known as hub. The hub has a diameter of `2.5 nm`. From the hub, develops 9 proteinaceous strands towards the peripheral triplet fibrils called radial fibres or spokes.