Actin filaments and microtubules are dynamic, turning over many times during their functional lifetimes. These polymers also are polar, in the sense of having different biochemical properties at each end. Their dynamic behavior and polarity are enhanced by free energy from the hydrolysis of nucleoside triphosphates. The biochemical properties of cytoskeletal polymers themselves appear to be widely conserved among eukaryotes. The different functions of the cytoskeleton are mediated by various accessory proteins, which assemble, disassemble, bundle, sever, cap, cross-link, or move the polymers.
Actin filaments play starring roles in organelle movement.
Microtubules are important for cell polarity and for controlling the direction of cell expansion. The cytoskeleton provides the machinery that separates the replicated chromosomes at mitosis and that partitions the daughter cells at cytokinesis. Mitosis depends on the mitotic spindle, a structure built largely from microtubules. Spindle microtubules interact with chromosomes at the kinetochore, a specialized protein-rich region that forms at the centromere. The dynamic properties of the microtubules, the architecture of the spindle, and the force-generating proteins at the kinetochore participate jointly in chromosome movement.