During mitosis, spindle fibers are responsible for moving chromatids around. These spindle fibers are specialized microtubule structures that guide the movement of chromosomes and chromatids during mitosis. During metaphase, the chromosomes travel to the center of the cell and align, allowing spindle fibers to bind to the center of each chromosome. The spindle fibers contract during anaphase, separating the sister chromatids and pulling them to opposite poles of the cell. Therefore, spindle fibers move chromatids during mitosis.