Cytokinesis

Cytokinesis (/ˌsaɪtoʊkɪˈniːsɪs/) is the final stage of cell division in the cell cycle, following mitosis. During cytokinesis the cytoplasm of a single eukaryotic cell is divided into two daughter cells. The cell's spindle apparatus partitions and transports duplicated chromatids into the cytoplasm of the separating daughter cells. It thereby ensures that chromosome number and complement are maintained from one generation to the next and that, except in special cases, the daughter cells will be functional copies of the parent cell.

Particular functions demand asymmetric cell division; for example, in oogenesis in animals, the ovum takes almost all the cytoplasm and organelles. This leaves very little for the resulting polar bodies, which in most species die without function, though they do take on various special functions in other species. Another form of mitosis occurs in tissues such as liver and skeletal muscle that omits cytokinesis, thereby yielding multinucleated cells (see syncytium).

Plant cytokinesis differs from animal cytokinesis, partly because of the rigidity of plant cell walls. Instead of plant cells forming a cleavage furrow such as develops between animal daughter cells, a dividing structure known as the cell plate forms in the cytoplasm and grows into a new, doubled cell wall between plant daughter cells. It divides the cell into two daughter cells.

Cytokinesis largely resembles the prokaryotic process of binary fission, but because of differences between prokaryotic and eukaryotic cell structures and functions, the mechanisms differ. For instance, a bacterial cell has a single circular chromosome, in contrast to the linear, usually multiple, chromosomes of a eukaryotic cell. Accordingly, bacteria construct no mitotic spindle in cell division. Also, duplication of prokaryotic DNA takes place during the actual separation of chromosomes; in mitosis, duplication takes place during the interphase before mitosis begins, though the daughter chromatids don't separate completely before the anaphase.