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MITOSIS
The nature of replicating cells
Reproduction: Not as simple as it loo
Reproduction presents a major problem for cells and organisms:
(how can information be transmitted faithfully to progeny)
= one bit of
genetic information
I
II
III
IV
The information transfer problem becomes more challenging as
more bits of information are incorporated into the organism
= one bit of
genetic information
One of life’s solutions to this challenge: “Package” the
bits of information into single units called chromosomes
= one bit of
genetic information
Packaging of genetic material in prokaryotes and eukaryotes
prokaryote cell
eukaryote cell
chromosomes
© 2003 John Wiley and Sons Publishers
Fig
2.4 The structure of a highly condensed, replicated chromosome.
A Chromosome
BASIC GENETICS
• Each cell in the human body contains two sets of 23
chromosomes
• Mitosis identically replicates this information
• Each cell therefore has the same
genetic material
• Reproductive cells only have
one set of chromosomes. These
combine to make a new person
with different genetic material to
both parents
The cell cycle.
© 2003 John Wiley and Sons Publishers
The Stages of the Cell Cycle
Mitosis
M stage
Mitotic Stage
The nucleus and cytoplasm
split to make two new cells
known as DIPLOID cells
STAGES OF MITOSIS
Every dividing tissue cell in the body is always
at a stage of the cell cycle. Whether it is at :Interphase
Prophase
Metaphase
Anaphase
Telophase
Diagram showing
the Stages of
Mitosis
Cytokinesis
Thus enabling the body
to continuously make
new body tissue for
growth and repair.
Prophase
The
Stages of
Mitosis
Interphase
Metaphase
Anaphase
Telophase
The Spindle
A spindle is a web type structure made up of
microtubule fibres. It is essential for mitosis
because it arranges the chromosomes into
their correct positions in preparation for cell
division.
Mitotic centre
A cell at metaphase
Microtubule
a spindle
Chromosomes attached to spindle
during nuclear division
INTERPHASE
After a cell has divided, the two
new cells begin the process again,
the cells at this stage are in
Interphase.
It is divided into three mini stages:Cell cycle
G1
S
G2
Eukaryotic chromsome replicating
PROPHASE
• The chromatin (unravelled DNA)
in the nucleus, condenses to
form pairs of chromosomes.
• As this is happening the nucleolus
begins to break down
• The centrioles move to opposite
ends of the nucleus.
• Nuclear membrane begins to break down
Prophase
• Chromatin
condenses
(remember that
chromatin/DNA
replicate during
Interphase), the
nuclear envelope
dissolves, centrioles
(if present) divide and
migrate, the spindle
forms.
METAPHASE
• The spindle becomes
fully developed
• The chromatid pairs
place themselves
onto individual fibres
and are aligned along
the centre of the
spindle
• The nuclear membrane has completely gone
ANAPHASE
• The chromatid pairs are
split into two
(This is done by movement
of the spindle fibres)
• The pairs then travel to
opposite ends of the
spindle
• The halved chromatids are
now called chromosomes
TELOPHASE
Two new nuclei are formed when
the chromosomes reach the
opposite poles of the cell
The nuclear membrane is formed- the nucleolus
reappears
The chromosomes disperse in the nucleus
REMEMBER!
Interphase
Prophase
Metaphase
Anaphase
Telophase
IPMAT
Mitosis in animal cells.
© 2003 John Wiley and Sons Publishers
CYTOKINESIS
Literally means, division of the
cytoplasm
Mitosis is the splitting of the nucleus.
Cytokinesis is the splitting of cytoplasm
It usually begins during ANAPHASE
Kangaroo epithelial
kidney cell going through
mitotic division.
The work of Mr Paul Maddox. The Mitosis World website.
Mitosis and cell plate
formation in a flattened
endosperm cell of the
African bloodlily
Haementhus Katherininae.
Observed with place contrast microscopy.
The work of Shinya Inoue and Rudolf Oldenbourge.The Mitosis World Website.
Cell Turnover - The speed of mitosis
Although you may have seen a speeded up video of
mitosis in action. One full cycle can vary between a
couple of minutes to days.
For example skin and epithelial cells have a rapid
turnover in the human body in order to replace the
ones constantly being worn away.
Cells which make up organs such as the eye and
the brain, need not multiply as often once they reach
adult size.
Click here for movies
Organs which need to
produce new cells
continuously have the
highest turnover.
For example:Bone marrowproducing replacement
blood cells
The testes - producing
semen
Tumours
Abnormalities can sometimes occur in cells
which reproduce at a rapid rate, this in turn may
lead to the formation of tumours.
Tumours of any type should be considered
serious.
Although benign tumours do not usually cause a
threat to a persons life, they can cause great
inconvenience if not treated.
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