Mitosis is the final stage of the cell cycle in which
replicated sister chromatids are separated and moved to opposite poles
of the cell and the cell splits into two daughter cells. Each daughter
cell receives a full set of chromosomes.
In eukaryotes, chromosomal DNA associates with proteins
called histones, which package the DNA into nucleosomes. During Prophase
(the first stage of mitosis), chromosomal DNA is tightly packaged
(chromosome condensation) into the X-shaped structures we typically
associate with chromosomes (eg. in karyotype analysis). In eukaryotes
other than fungi, the nuclear envelope and nucleolus disappear at
this point.
During Prometaphase, the duplicated
centrioles move apart and microtubules emanating from them interact
to form a bipolar mitotic spindle. Proteins associate with the centromeres
of chromosomes to form structures called kinetochores.
During Metaphase, k inetochores interact
with microtubules emanating from one of the poles of the bipolar mitotic
spindle and chromosomes move to the middle of the spindle and line
up. Microtubule interactions with the kinetochore are maintained during
most of mitosis and are largely (but not entirely) responsible for
moving chromosomes. Chromosome movements are accomplished by a combination
of microtubule polymerization and depolymerization, which push and
pull chromosomes, and the action of microtubule motor proteins present
at the kinetochore and/or spindle poles, which pull on microtubules
in a hand-over-hand manner.
During Anaphase, the chromosomes
move to the spindle poles. The spindle poles themselves also often
move apart when overlapping microtubule in the middle of the spindle
(non-kinetochore microtubules) slide past each other causing the spindle
to elongate. The interaction of astral microtubules (those microtubules
outside of the spindle) with the cell cortex may also contribule to
spindle elongation. During the later stages of anaphase, cytokinesis
(cell division) starts.
During Telophase, the
chromosomes decondense, the nuclear envelope reforms around the chromosomes
and cytokinesis produces two daughter cells.
