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Centrioles are cylindrical, microtubule‑based organelles present in most eukaryotic cells. Each is composed of nine triplet microtubule clusters that form a 500‑nm‑long, 200‑nm‑wide tube of alpha‑ and beta‑tubulin. In cilia and flagella the arrangement shifts to nine doublet clusters, which power motility. The centrioles sit inside the centrosome, a region enriched with over 100 proteins known as the pericentriolar material (PCM). This matrix, lacking a surrounding membrane, provides a scaffold for microtubule nucleation.
During mitosis a centrosome contains two pairs of centrioles and PCM. The centrosomes migrate to opposite poles of the nucleus, and microtubules radiate outward to form the mitotic spindle. Spindle fibers attach to chromosome centromeres at the metaphase plate, while the remaining fibers help push the daughter cells apart during cytokinesis.
Interphase—comprising G1, S, and G2—provides the cell with growth and DNA synthesis. The PCM is organized by the scaffold protein pericentrin, which anchors one end to centriole microtubules and extends radially to recruit other matrix components. The centrosome functions as a microtubule‑organizing center (MTOC) during this period.
In G1 the centrioles drift slightly apart and remain so until mitosis begins. Centriole duplication starts in late G1. During the S phase, each “mother” centriole nucleates a “daughter” centriole at right angles—a semi‑conservative process analogous to DNA replication. By G2 the daughter centrioles grow in size, and mother centrioles recruit additional PCM in preparation for spindle assembly.
Basal bodies are unpaired centrioles that serve as the foundation for cilia and flagella. Encircled by PCM, the basal body’s microtubules drive the beating of cilia in respiratory epithelium or the flagella of sperm. The microtubule motor proteins within these structures dictate movement direction and rhythm.
Many cancer cells possess supernumerary centrosomes, a phenotype often linked to mutations in the p53 tumor‑suppressor gene. Excess centrosomes can lead to chromosomal instability. Chemotherapeutic agents such as vincristine and paclitaxel target microtubule dynamics, disrupting spindle formation and arresting cell division.
