Centrosome
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The centrosome is the main microtubule organising centre of the cell (MTOC). It is composed of two orthogonally arranged centrioles surrounded by an amorphous mass of pericentriolar material (PCM). It is one of the only non-membrane bound organelles, of the cell. The centrosome nucleates and organises microtubules. It plays a central role in cell division. and in making cilia and flagella.
Higher eukaryotic cells posses a centrosome. Yeast cells have a spindle pole body (SPB) which is their centrosome equivalent. The SPB differs from the centrosome in many ways, but namely it does not possess any centrioles. Plant cells do not have centrosomes.
The centrosome must replicate once and only once per cell cycle so that each daughter cell can inherit one centrosome. Aberrant numbers of centrosomes in a cell have been associated with cancer. The centrosome replicates during the S phase of the cell cycle. During the prophase of mitosis, the centrosomes migrate to opposite poles of the cell. Between them is formed the mitotic spindle, a bundle of microtubules that will function later as the foundation for cell division. Interestingly, the pair of centrioles that make up each centrosome is not apparently necessary for the creation of the spindle. When the centrioles are destroyed, for example by a laser, the spindle nonetheless forms and cell division procedes normally, but cells arrest in the following cell cycle.de:Centrosom nl:Centrosoom pl:Centrosom