Cytokinesis
Cytokinesis is the physical division of a cell's cytoplasm, usually after nuclear division, producing separate daughter cells with their own membranes and cellular contents.
What cytokinesis is
Cytokinesis is the process that physically divides a cell's cytoplasm. It usually follows or overlaps the end of mitosis or meiosis, when chromosomes have already been separated into new nuclei. Without cytokinesis, nuclear division could produce a cell with multiple nuclei rather than two separate daughter cells.
How it fits the cell cycle
In the cell cycle, mitosis separates duplicated chromosomes, while cytokinesis separates the rest of the cell. These processes are often grouped together in M phase because they are closely coordinated. The timing matters: the cell must avoid cutting through chromosomes or leaving essential contents behind.
Animal cell cleavage
In many animal cells, cytokinesis begins with a cleavage furrow. A contractile ring of actin filaments and myosin motor proteins tightens around the cell's middle, drawing the membrane inward. As the furrow deepens, the cell narrows until the two daughter cells separate.
Plant cell plates
Plant cells cannot simply pinch inward because a rigid cell wall surrounds the plasma membrane. Instead, vesicles gather near the cell center and fuse to form a cell plate. The plate expands outward and becomes part of the new cell wall and plasma membranes between daughter cells.
Cytoskeleton and positioning
Cytokinesis depends heavily on the cytoskeleton. Microtubules help position the division plane, while actin and myosin provide contractile force in many animal cells. The division site must line up with where chromosomes were separated so each daughter cell inherits an appropriate nucleus.
Membranes and cargo
Dividing a cell also means managing membrane supply and cellular contents. Vesicles can deliver new membrane, enzymes, and wall-building material. Organelles and cytoplasmic components must be distributed well enough that both daughter cells can survive and resume normal activity.
When cytokinesis fails
Failed or incomplete cytokinesis can leave cells with two or more nuclei, abnormal chromosome content, or unusual size. Some organisms and tissues use multinucleate cells normally, but accidental cytokinesis failure can contribute to developmental problems, genomic instability, or cancer-related changes.
Why it matters
Cytokinesis matters because division is not finished when chromosomes separate. A new cell must be physically made. By coordinating membranes, cytoskeletal force, vesicle traffic, and chromosome position, cytokinesis turns one organized cell into two workable descendants.