Centrosome & Centrioles,It s Structure,Function!!

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1 Centrosome & Centrioles,It s Structure,Function!! CENTROSOME In cell biology, the centrosome (Latin centrum center and Greek soma body ) is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell. It regulates the cell division cycle. The centrosome was discovered by Edourad Van Beneden in 1883 and was described and named in 1888 by Theodor Boveri. STRUCTURE OF CENTROSOME Centrosomes are composed of two orthogonally arranged centrioles surrounded by an amorphous mass of protein termed the pericentriolar material (PCM).the PCM contains proteins responsible for microtubules nucleation and anchoring. In general each centriole of the centrosome is based on nine triplet microtubule assembled in a cartwheel structure and contains centrin, connexion and tektin.

2 FUNCTION OF CENTROSOME Centrosomes are associated with the nuclear membrane during prophase of the cell cycle. In mitosis the nuclear membrane breaks down and the centrosome nucleated microtubules can interact with the chromosome to build the mitotic spindle. The mother centriole, the older of the two in the centriole pair, also has a central role in making cilia and flagella. The centrosome replicates during the S phase of the cell cycle. During the prophase in mitosis, the centrosomes migrate to opposite poles of the cell. The mitotic spindle then forms between two centrosome. Upon divisions, each daughter cell receives one centrosome. In the absence of the centrioles the microtubules of the spindle are focused by motors allowing the formation of a bipolar spindle. Aberrant numbers of centrosomes in a cell have been associated with cancer. CENTRIOLES In animal cells have two organelles known as centrioles.

3 The centrioles play a major role in cell division. In animal cells the centrioles plays a major role in cell division but in the plant cells have the ability to reproduce even without the centrioles. STRUCTURE OF CENTRIOLES The centrioles are cylindrical shaped cellular organelles. They are found in most eukaryotic cells. The centrioles are made of groups of microtubules. These microtubules are arranged in a in a pattern of 9+3. The pattern of the microtubules for a ring of 9

4 microtubules known as triplets and microtubules are arranged at right angles to one another. Each triplet fibers are composed of three sub fibers or sub tubules. The sub tubules are made up of protein tubulin. All the structure that surrounds the centrioles together constitutes the centriole satellite. The number of these satellites varies. FUNCTIONS OF CENTRIOLES In higher animal cells centrioles form mitotic poles. The centrioles functions as the microtubules organizing center. It is important event in major cellular process that is cell division and flagella formation. The centrioles pair duplicates within a cell and the two pairs migrate to the opposite ends of the cell to organize the mitotic spindle or spindle fibers. Each centriole gives rise to a new centriole. The

5 centrioles that are newly formed remain tightly attached to the parent centriole and it elongates during the S and G2 phase. In the prophase stage the centrioles pairs start moving towards the opposite poles of cell, and also forms the spindle fibers simultaneously. The migration of the positioning of the centrioles determines the orientation of the spindle. It also influences the chromosomes attachment to the spindle fibers. The spindle fibers are responsible for the segregation of chromosomes into the daughter cells. At the end of each cell cycle, the cell has two centrioles. One the mother centriole and the other newly formed centriole which is the daughter centriole. The centrioles may produce flagella or cilia. The fiber of the tail of sperms also arises from the centrioles. This is the general notes on Centrosome and Centriole. Thank You.