Centrosome & Centrioles
Two cylindrical structures has centrosome organelle called centrioles, which are surrounded by a cloud of amorphous pericentriolar material called centrosphere or kinoplasm. These two centrioles called diplosomes are localised in the centrosome at right angles to each other.
The centriole are found in almost all eukaryotic cells like animal cells, fungi & algae but not found in higher plant cells.
Structure of a Centrioles
(i) A centriole possesses a whorl of nine evenly spaced peripheral fibrils of tubulin. It is absent in the centre. Therefore, the arrangement is called 9 + 0.
(ii) Each fibril is made up of three subfibres. Threfore, it is called triplet fibril consisting of sub – fibres A, B, C.
(iii) The adjacent triplet fibrils are connected by C – A proteinaceous linkers.
(iv) The centre of the centriole possesses a rod – shaped proteinaceous mass known as hub. From the hub, nine proteinaceous strands are developed towards the peripheral triplet fibrils. These strands are called radial spokes.
(v) Due to the presence of radial spokes & peripheral fibrils, the centriole gives a cartwheel appearance.
(vi) There is no membrane boundary for a centriole, but it is surrounded by pericentriolar satellites, also known as massule (Microtubule generator or MTG)
(i) Centrioles help in the formation of basal bodoes which give rise to cilia & flagella.
(ii) Centrioles from the spindle fibres that give rise to spindle apparatus during cell division.