Structure and composition of the centrosome
The centrosome is made up of:
- Two centrioles or diplosome. The structure of the centrioles is identical to that of the basal corpuscles of the cilia. They occupy the center of the centrosome. They are oriented perpendicular to each other. Each centriole is cylinder-shaped, with walls formed by nine triplets of microtubules, without any central microtubule, forming the so-called 9 + 0 structure.
The microtubules that make up triplets are called:
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- Microtubule A: the innermost microtubule, circular in section (13 protofilaments), and closest to the axis of the cylinder.
- Microtubule B: located between microtubules A and C. Its section is shaped like a half moon, and it shares 3 protofilaments with microtubule A.
- Microtubule C: the outermost. It also has a crescent-shaped section and shares 3 protofilaments with microtubule B.
The triplets are linked together by a bridge formed by a protein called nexin.
When the cell divides, the centrioles double, and each diplosome goes to a daughter cell.
In cell division, each of the centrioles gives rise, by duplication, to its partner. In this way, two diplosomes are obtained, one for each daughter cell.
- The pericentriolar material or centrosphere surrounds the diplosome. It is an optically dense material.
The microtubule organizing center (COMT) is the set of centrioles and pericentriolar material.
- The aster, fibers made up of microtubules that grow and are organized radially around the centrosome. Aster microtubules give rise to achromatic spindle microtubules in cell division.
The centrosome or cytocenter is called the set of diplosome, centrosphere and aster.
All microtubule structures such as cilia, flagella and the achromatic spindle come from the centriole. Although the cell does not have centrioles, the pericentriolar material and aster fibers will appear.