Two centrioles are arranged perpendicularly and surrounded by further proteins (the pericentriolar material) to form the centrosome. The centrosome is also known as the microtubule organizing center (MTOC). The MTOC plays an important role in microtuble organization in the cell. All microtubules are anchored at their (-) end while they grow away from the MTOC in the (+) direction.
Centrioles are important in the cell division process, organizing the mitotic spindle upon which the chromosomes are pulled apart. Some animal cells are able to divide their chromosomes without centrioles, for instance in female meiosis. Centrioles assist the cell through the process of mitosis and in male meiosis. During cell division the centrioles are copied, so that there will be a pair for each daughter cell. In replication, each new set of centrioles is composed of one original centriole, and a newly made centriole. If the centrioles are used in forming flagella or cilia, the oldest of the two centrioles becomes the main base for that structure. This is one reason why each set of newly replicated centrioles receives one centriole from the original cell and a newly formed centriole, so that the cell will know which one to allow to form flagella or cilia.
The proteins which make up the centrioles of the green alga Chlamydomonas reinhardtii have been determined. In Chlamydomonas, centrioles play an important role in the formation and movement of flagella. The centriole acts as the base of the flagellum, from which nine doublets of the flagellar axoneme are templated from the original 9 triplet microtubules of that centriole.
Centrioles are structurally identical to the
basal body.
