Structure of centrioles:
A centriole possesses a whorl of nine peripheral fibrils. Fibrils are absent in the centre. The arrangement is, therefore, called 9+0 which runs parallel to one another but an angle of 40 degrees. Each fibril is made up of three sub fibres called triplet fibril. The three sub fibres in reality micro tubules joined together by their margins and therefore sharing the common walls made of two-three proto filaments. Each sub fibre has a diameter of 25nm. From outside to inside the three sub fibers of a triplet fibril are named as C, B and A respectively.
The sub fibre A is regarded to be complete with 13 proto filaments while B and C sub fibres are incomplete due to sharing of some micro filaments.
The adjacent triplet fibrils are connected by C-A proteinaceous linkers. The centre of centriole possesses a rod shaped proteinaceous mass known as hub. The hub has a diameter of 2.5 nm. From the hub, develops nine proteinaceous strands towards the peripheral triplet fibrils called radical fibres or spokes.
Functions of centrioles:
Though centrioles have not been found to contain DNA yet they are capable of forming new centrioles with the help of massules or pericentriolar satellites which function as nucleating centres.
Centrioles help in cell division by forming spindle poles or micro tubules organizing centres (MTOCs)
Out of the two centrioles in a spermatozoan, the distal one gives raise to axial filament or tail.
Centrioles can be transformed into basal bodies which give raise to cilia and flagella.