The Mitotic Division of an Animal Cell

a nuclear envelope bounds the nucleus
the nucleus contains one or more nucleoli

two centrosomes have formed by relpication of a single centrosome

in animal cells, each centrosome features two centrioles

chromosomes, duplicated during S phase, cannot be seen individually beacuse they have not yet condensed

the chromatin fibers become more tightly coled, condensing into discrete chromosomes observable with a light microscope

the nucleoli disappear

each duplicated chromosome appears as two identical sister chromatids joined together at their centromeres and all along their arms by cohesins (sister chromatid cohesion)

the mitotic spindle begins to form. it is composed of the centrosomes and the microtubules that extend from them. the radial arrays of shorter microtubules that extend from the centrosomes are called asters

the centrosomes move away from each other, apparently propelled by the lengthening microtubules between them

the nuclear envelope fragments

the microtubuels extending from each centrosome can now invade the nuclear area

the chromosomes have become even more condesnsed

each of the two chromatids of each chromosome now has a kinetochore, a specialized structure located at the centromere

some of the microtubules attach to the kinetochores, becoming "kinetochore microtubules"; these jerk the chromosomes back and forth

nonkinetochore microtubules interact with those from the opposite pole of the spindle

longest stage of mitosis, often lasting about 20 minutes

the centrosomes are now at opposite poles of the cell

the chromosomes convene on the metaphase plate, an imaginary plane that is equidistant between the spindle's two poles. the chromosomes' centromeres lie on the metaphase plate

for each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles

shortest stage of mitosis, often lasting only a few minutes

begins when the cohesin proteins are cleaved; allows the two sister chromatids of each pair to part suddenl; each chromatid thus becomes a full-fledged chromosome

the two liberated daughter chromosomes begin moving twoard opposite ends of the cells as their kinetochore microtubules shorten. Because these microtubues are attached at the centromere region, the chromosomes move centromere first

the cell elongates as the nonkinetochore microtubules lengthen

by the end of anaphase. the two ends of the cell have equivalent- and complete- collections of chromosomes

two daughter nuclei form in the cell

nuclear envelopes arise from the fragments of the parent cell's nuclear envelope and other portions of the endomembrane system

nucleoli reappear

the chromosomes become less condesnsed

mitosis, the division of one nucleus into two genetically identical nuclei is now complete

the division of the cytoplasm is usually well under way by late telophse, so the two daughter cells appear shortly after the end of mitosis

in animal cells, this involves the formation of a cleavage furrow, which pinches the cell in two