What is the mitotic spindle primarily composed of?

The mitotic spindle is primarily composed of microtubules, which are dynamic structures made up of the protein tubulin. During cell division, microtubules form the spindle fibers that help separate duplicated chromosomes into two daughter cells. These microtubules are organized in a specific arrangement, with some extending from the centrosomes to the chromosomes and others connecting the centrosomes to one another, creating a robust structure that ensures accurate chromosome segregation.

Microtubules can rapidly grow and shrink, allowing the spindle to respond to the spatial organization of chromosomes during various stages of mitosis. This dynamic instability is crucial for the proper attachment of spindle fibers to kinetochores, structures on chromosomes that facilitate their movement. The ability of microtubules to reorganize during the cell cycle is integral for successful cell division, highlighting their primary role in the structure and function of the mitotic spindle.