centrioles

Centrioles are cylindrical organelles found in the cytoplasm of most animal cells and in some other eukaryotes. They are a core component of the centrosome, the primary microtubule organizing center, and usually occur as a pair arranged at right angles to each other, embedded in pericentriolar material.

Structure and composition: Each centriole is a hollow, rod-like structure about 0.2–0.5 micrometers long and 0.15–0.25 micrometers in diameter. It is built from nine triplets of fasciculated microtubules arranged in a cylindrical pattern with a characteristic cartwheel organization during assembly. The centrosome contains gamma-tubulin and other proteins that nucleate and organize microtubules around the centrioles.

Functions: Centrioles contribute to the organization of the mitotic spindle, guiding the assembly and orientation of microtubules that segregate chromosomes during cell division. They also serve as basal bodies that template the formation of cilia and flagella in cells that possess them. Centriole duplication is coordinated with the cell cycle to ensure that each daughter cell inherits a pair of centrioles.

Duplication and occurrence: Centrioles duplicate once per cell cycle, typically during the S phase, to produce two new centrioles per existing pair. While common in animal cells, centrioles are absent or reduced in most plant and fungal somatic cells; some algae and other protists retain centrioles or their basal body equivalents.

Clinical relevance: Abnormal centriole number or function can disrupt spindle assembly and chromosome segregation, a feature associated with cancer and certain developmental disorders such as microcephaly.