11th Class Biology Cell - The Unit Of Life Centrosome

Discovery : Centrosome was first discovered by Van Benden (1887) and structure was given by T. Boweri.

Occurrence : It is found in all the animal cell except mature mammalian RBC’s. It is also found in most of protists and motile plant cells like antherozoids of ferns, zoospores of algae and motile algal forms e.g., Chlamydomonas but is absent in prokaryotes, fungi, gymnosperms and angiosperms.

Structure : Centrosome is without unit membrane structure. It is formed of two darkly stained granules called centrioles, which are collectively called diplosome. These centrioles are surrounded by a transparent cytoplasmic area called centrosphere of Kinetoplasm. Centriole and centrosphere are collectively called centrosome. Each centriole is a microtubular structure and is formed of microtubules arranged in 9+0 manner (all the 9 microtubules are peripheral in position). Inside the microtubules, there is an intra-centriolar or cart-wheel structure which is formed of a central hub (about \[25{AA}\] in diameter) and 9 radial spokes or radial fibres.

Chemical composition : Centrosome is lipoproteinaceous structure. The microtubules of centriole are composed of protein tubulin and some lipids. They are rich in ATPase enzyme.

Origin : The daughter centriole is formed from the pre-existing centriole in \[{{G}_{2}}\] of interphase so called self-replicating organelle.

Functions

(1) The centrioles help organising the spindle fibres and astral rays during cell division.

(2) They provide basal bodies which give rise to cilia and flagella.