Centrosomes Essay

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Centrosomes are cytoplasmic organelles which contain two centrioles (mother and daughter centriole) positioned perpendicular to each other. Each centriole is a cylindrical structure, ~100-150 nm in diameter and 100- 400 nm in length, made up of nine microtubule triplets (singles or doublets in some cells) (Delattre and Gönczy, 2004). The centrosome is surrounded by pericentriolar material (PCM) which helps in nucleating microtubules. The PCM contains pericentrin, centrin, γ-tubulin ring complexes (γ-TuRC). The γ-TuRC initiates microtubule polymerization, which involves the repeated addition of α and β subunits. The centrosome functions as a Microtubule Organising Center (MTOC) in animal cells. Fungal and plants cells do not possess centrosomes, and instead use other MTOCs (e.g. yeast cells have Spindle Pole Bodies (SPBs)).

Centrosome biogenesis is initiated in the G1 phase. The centrosome duplication cycle which is normally coordinated with the cell cycle, also faces exceptions in the case of spermatogenesis in which centrosome duplication occurs before the second meosis, and in cancer cell. …show more content…

The two new pair of centrioles arise from the proximal end of each of the older centrioles, and elongate to reach the same length as the parent centrioles. The original mother and daughter centrioles completely separate from each other, along with their new daughter centrioles to form two new centrosomes. Each of the two resulting centrosomes thus contain one centriol from the older generation and one newly formed centriole (semiconservative replication). The PCM also gets divided between the two new centrosomes. The sequence of steps of the centrosome duplicaiton cycle shows variations in some cells. For example, in Drosophila melanogaster embryo, the PCM divides before the new daughter centrioles are

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