Mitosis and cytokinesis

Prophase: replicated chromatin condenses (condensins) into visible chromosomes, each of two sister chromatids held together by cohesin; the nucleolus disperses; the two centrosomes move apart and nucleate the mitotic spindle. Prometaphase: CDK1 phosphorylates lamins and nucleoporins and the nuclear envelope breaks down; spindle microtubules "search and capture" chromosomes at their kinetochores (protein complexes on the centromeres). Metaphase: chromosomes are pulled back and forth until they align at the metaphase plate (equatorial plane), with sister kinetochores attached to opposite poles (bi-orientation). The spindle-assembly checkpoint waits until every kinetochore is attached.

Anaphase: APC/C–Cdc20 ubiquitinates securin (and cyclin B) for proteasomal destruction; freed separase cleaves cohesin and the sister chromatids separate abruptly — now called daughter chromosomes. In anaphase A they move toward the poles as kinetochore microtubules shorten; in anaphase B the poles move apart as overlapping polar microtubules slide (kinesin-5) and astral microtubules are pulled by cortical dynein. Telophase: chromosomes arrive at the poles and decondense; the nuclear envelope re-forms around each set; nucleoli reappear.

Cytokinesis usually begins in late anaphase: a contractile ring of actin and myosin II assembles beneath the plasma membrane at the former metaphase plate (positioned by the spindle midzone) and constricts, forming a cleavage furrow that pinches the cell into two; the final bridge (midbody) is cut by ESCRT proteins. Mitosis takes about an hour.