Kinetochores are the protein structures where spindle fibers attach on chromatids; this happens during cell division and is used to pull sister chromatids apart. Kinetochores start — and are in charge of — the movements of chromosomes during cell division.
Each sister chromatid is held together with its own kinetochore during mitosis. The kinetochore faces the opposite direction, and then attaches to the opposite poles of the mitotic spindle. The kinetochore has two parts: the inner and outer sections. The inner part is associated with the centromere DNA, which is persistent throughout the cell cycle. The outer part has many parts that only function during cell division. This portion of the kinetochore also reacts with the microtubules.