Diagram of Mitosis
This follows the page about the
context of mitosis - explaining its position in the
sequence of processes that, together,
form the
"cell cycle"
for somatic cells.
Definition: Mitosis is defined as the type of cell division
by which a single cell divides in such a way as to produce two
genertically
identical "daughter cells". This is the method by which
the body produces new cells for both growth and repair of aging
or damaged tissues throughout the body - as opposed to for sexual
reproduction (when meiosis applies).
Mitosis is the simplest of the two ways (mitosis and meiosis)
in which the nucleus of a cell can divide - as part of a process
of whole cell division. The four stages of mitosis (prophase, metaphase,
anaphase and telophase) are illustrated and described below.
Mitosis (Nuclear Division)
0.
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Interphase
Interphase is not part of mitosis but is included
here as a reminder that interphase preceeds
mitosis.
(Hence, it has the number 0.)
Chromatin is material in a cell nucleus
consisting of DNA and protein. This is the substance
that chromosomes are made from. It can be stained
with dyes in order to
watch the process of mitosis using a microscope. |
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1. |
Prophase
- Early in the prophase stage the chromatin fibres shorten
into chromosomes that are visible under a light microscope. (Each
prophase chromosome consists of a pair of identical double-stranded
chromatids.)
- Later in prophase, the nucleolus disappears, the nuclear
envelope breaks down, and the two centrosomes begin to
form the miotic spindle (which is an assembly
of microtubules).
- As the microtubules extend in length between the centrosomes,
the centrosomes are pushed to opposite "poles" (extremes)
of the cell.
- Eventually, the spindle extends between two opposite
poles of the cell.
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2. |
Metaphase
Metaphase is characterized by the "metaphase
plate". This
is a mid-point region within the cell that is formed/defined
by the centromeres of the chromatid pairs aligning along
the
microtubules
at the centre of the miotic spindle. |
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3. |
Anaphase
- The centromeres split seperating the two members of each
chromatid pair - which then move to the opposite poles
of the cell: When they are seperated the chromatids
are called chromosomes.
- As the chromosomes are pulled by the the microtubules
during anaphase, they appear to be "V"-shaped because the
centromeres lead the way, dragging the trailing arms of
the chromosomes
towards the pole/s.
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4.
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Telophase
- Telophase begins after the chromosomal movement stops.
- The identical sets of chromosomes - which are by this
stage at opposite poles of the cell, uncoil and revert
to the long, thin, thread-like chromatin form.
- A new nuclear envelope forms around each chromatin
mass.
- Nucleoli appear.
- Eventually the miotic spindle breaks-up.
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0. |
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Two new "daughter cells" - the cycle is about to
repeat itself.
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Interphase - see top of page
The cycle is about to start again ...
Interphase is not part of mitosis but is included here as
a reminder that interphase preceeds mitosis.
(Hence, it has the number 0.)
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... then the cytoplasm begins to divide around the two new nuclei
- which is called Cytokinesis
(Cytoplasmic Division).
When cytokinesis is complete, interphase
begins (see further up this page). This begins the next "cell cycle".
Go back to read about the
context of mitosis or go on to read the page about
cell division via meiosis.
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