Virtual Lab: Mitosis Phases
Overview
Mitosis and Cytokinesis
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There are four stages in mitosis: prophase, metaphase, anaphase, and telophase. The
essence of the process is that duplicated chromosomes line up along an equatorial
plane of the parent cell, called the metaphase plate, with the sister chromatids that make
up each duplicated chromosome lying on opposite sides of the plate. Attached to fibers
called microtubules, the sister chromatids are then pulled apart, to opposite poles of the
parent cell. Once cell division is complete, sister chromatids that once formed a single
chromosome will reside in separate daughter cells, with each sister chromatid now
functioning as a full-fledged chromosome.
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Cytokinesis in animal cells works through a ring of protein filaments that tightens at the
middle of a dividing cell. Membranes on the portions of the cell being pinched together
then fuse, resulting in two daughter cells.
Variations in Cell Division
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Because of their cell walls, plant cells must carry out cytokinesis differently from animal
cells. The plant’s solution is to grow new cell walls and plasma membranes near the
metaphase plate, thus dividing the parent cell into two daughter cells. Prokaryotes such
as bacteria employ a process called binary fission: They double their single, circular
chromosome, with the two resulting chromosomes attaching to different sites on the
plasma membrane. Then an outgrowth of plasma membrane and cell wall, called a
septum, begins growing from opposite sides of the cell, in between the two
chromosomes. When the two septum extensions join in the middle, they divide the one
cell into two.