mitosis the nature of replicating cells. reproduction: not as simple as it looks
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MITOSISMITOSISThe nature of replicating cellsThe nature of replicating cells
Reproduction: Not as simple as it looks.
Reproduction presents a major problem for cells and organisms: (how can information be transmitted faithfully to progeny)
I
II
III
IV
= one bit ofgenetic information
= one bit ofgenetic information
The information transfer problem becomes more challenging as more bits of information are incorporated into the organism
One of life’s solutions to this challenge: “Package” the
bits of information into single units called chromosomes
= one bit ofgenetic information
chromosomes
Packaging of genetic material in prokaryotes and eukaryotes
prokaryote cell
eukaryote cell
Fig 2.4 The structure of a highly condensed, replicated chromosome.© 2003 John Wiley and Sons Publishers
A Chromosome
BASIC GENETICSBASIC 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
Mitosis
The The SStages of the tages of the CCell ell CCycleycle
M stageM stageMitotic Stage
The nucleus and cytoplasm split to make two new cells
known as DIPLOID cells
Every dividing tissue cell in the body is always at a stage of the cell cycle. Whether it is at :-
STAGES OF MITOSISSTAGES OF MITOSIS
Cytokinesis
Thus enabling the body
to continuously make
new body tissue for
growth and repair.
Diagram showing the Stages of
Mitosis
Prophase
MetaphaseAnaphase
Telophase
Interphase
Prophase
Metaphase
Anaphase Telophase
The The Stages Stages
of of MMitosisitosisInterphase
The SpindleThe 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
MicrotubuleA cell at metaphase a spindle
Chromosomes attached to spindle during nuclear division
INTERPHASEINTERPHASE
After a cell has divided, the two
new cells begin the process again,
the cells at this stage are in
Interphase.
Cell cycle
It is divided into three mini stages:- G1
S
G2
Eukaryotic chromsome replicating
PROPHASEPROPHASE• The chromatin (unravelled DNA)
in the nucleus, condenses to form pairs of chromosomes.
• The centrioles move to opposite ends of the nucleus.
• As this is happening the nucleolus
begins to break down
• 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.
METAPHASEMETAPHASE
• The spindle becomes fully developed
• The nuclear membrane has completely gone
• The chromatid pairs place themselves onto individual fibres and are aligned along the centre of the spindle
ANAPHASEANAPHASE
• 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
TELOPHASETELOPHASETwo 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!REMEMBER!
IInterphase
PProphase
MMetaphase
AAnaphase
TTelophase
IPMAIPMATT
Mitosis in animal cells.
© 2003 John Wiley and Sons Publishers
CYTOKINESISCYTOKINESIS
Literally means, division of the
cytoplasm
Mitosis is the splitting of the nucleus.
Cytokinesis is the splitting of cytoplasm
It usually begins during ANAPHASE
Observed with place contrast microscopy.
The work of Shinya Inoue and Rudolf Oldenbourge.The Mitosis World Website.
The work of Mr Paul Maddox. The Mitosis World website.
Kangaroo epithelial kidney cell going through mitotic division.
Mitosis and cell plate formation in a flattened endosperm cell of the African bloodlily Haementhus Katherininae.
Cell Turnover - Cell Turnover - The speed of The speed of mitosismitosis
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 marrow-
producing replacement
blood cells
The testes - producing
semen
TumoursTumours
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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