Question

In cilia microtubular fibrils are of doublet nature and are tilted by 10° angle so that subfebrilA is close to center. In centriole, microtubular fibrils are triplet nature and are tilted by?
A.$10^\circ $
B.$30^\circ $
C.$40^\circ $
D.$45^\circ $

Answer 1

Hint:- Centriole is a cylindrical organelle found in most of the eukaryotic cells including humans. Centrioles are absent in conifers, angiosperms, etc. Centrioles are involved in spindle formation and help the cell during cell division. The absence of centrioles causes error in cell division leading to delay in the mitotic process.

Complete step-by-step solution:-The centriole is made up of a hollow tube-like structure made up of tubulin and microtubules which lies parallel to one another and arranged around the central cavity to form a cylindrical structure. Centrioles are usually $0.15$-$0.25$ um in diameter and $0.30$-$0.70$ um in length. Each cell consists of a pair of centrioles in a region called the centrosome near the nucleus. Centrioles are small, microscopic, microtubular cylinders having nine triplet fibrils.
Centriole consists of a whorl of nine peripheral fibrils which are absent in the center, thus giving a $9 + 0$ type of arrangement. Each fibril is composed of three sub-fibrils making it a triplet fibril structure. These microtubular fibrils are arranged at an angle of $40^\circ $ with each other. These triplet fibrils are joined together having a common wall made up of proto-filaments.
The Centre of the centriole consists of a rod-shaped proteinaceous structure called Hub which is $2.5$ nm in diameter. From the hub, $9$ protein strands arise towards triplet fibrils called Spokes. A typical centriole due to the presence of radial spokes and the peripheral fibrils gives a characteristic Cartwheel appearance in the transverse section. So, the correct answer is an option (C) $40^\circ $.

Note:-
Centrosome is a structure that consists of a pair of centrioles arranged in a $9 + 0$ type of arrangement. The two centrioles lie at an angle of $90^\circ $ with each other. The two perpendicular centrioles consist of a daughter centriole and a mother centriole which are joined together by interconnecting fibers. The two perpendicular centrioles are surrounded by amorphous pericentriolar matrices.