centriole

Centrioles organize the spindle apparatus on which the chromosomes move during mitosis. Cilia and flagella are organized from peripheral centrioles (basal bodies).

Centrioles consist of 9 sets of triplet microtubules, and centrioles are arranged in pairs perpendicular to each other (tem - 9 triplet pair). animation - spinning centriole pair : tour centriole : zoom in on centriole. Unlike cilia and flagella, which are organized from microtubule organizing centers (basal bodies) at the cell periphery, centrioles have no central doublet of microtubules. Centrioles replicate autonomously, beginning from centers that contain proteins needed for their formation (tubulin, etc.). Procentrioles form first, each erecting a single microtubule from which the triplet can form (diagram - centriole formation). After a single centriole is constructed, daughter centrioles grow out from the tubules at right angles. In a non-dividing cell, they move to the periphery to form the basal body for the cilium (tem - basal bodies). In a dividing cell, the second centriole moves to the daughter cell (in a dividing cell). Where spindles are essential for chromosomal separation during reproduction, cilia are essential for cellular differentiation during embryologic development.

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