The centrosome is an organelle containing two cylindrical structures called centrioles, composed of tubulin strands held together by interlocking arms of dynein protein. Centrioles serve as the anchor points for microtubules that form the mitotic spindle during mitosis. Consequently, the centrosome is sometimes called the microtubule organizing center.
Centrosomes are found almost exclusively in animal cells. A few protozoans contain structures called basal bodies, which are similar to centrioles. Plant cells and fungi contain a poorly defined microtubule organizing center that lacks centrioles entirely. However, these cells undergo mitosis as effectively as their animal cell counterparts. As such, biologists continue to debate the exact role that centrioles play in mitosis ? possibly as a safeguard against chromosomal misalignment ? as well as when and how these structures arose in the course of cellular evolution.