The document discusses cell division and the cell cycle. It notes that cell division is necessary for growth, repair, and reproduction. There are two main types of cell division: mitosis and meiosis. Mitosis produces identical daughter cells and is involved in growth and repair, while meiosis occurs in sex cells and involves genetic variation. The cell cycle consists of interphase and mitosis. Interphase prepares the cell for division and consists of G1, S, and G2 phases. Mitosis then divides the cell into two identical daughter cells. Cancer occurs when cell division becomes uncontrolled and cells fail to differentiate. The document provides details on various stages of the cell cycle and cell division.

1. www.tastafe.tas.edu.au
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2. Cell division is necessary for bodily
growth, repair and reproduction
Herlihy 2011, p. 41
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3. The frequency of cell division varies from
one tissue to the next
Some cells reproduce frequently whereas
some reproduce slowly or not at all
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4. More than 2,000,000 red blood cells are replaced
every second!
sfdm.scad.edu
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5. Cells that line the digestive tract are
reproduced very few days …..
scitechdaily.com
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6. Certain nerve cells in the brain and spinal cord
do not reproduce at all
newswatch.nationalgeographic.com
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7. There are Two (2) Kinds of Cell
Division
1. Mitosis
2. Meiosis
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8. Mitosis
Is involved in bodily growth and repair
Mitosis involves the splitting of one mother
cell into two (2) identical “daughter cells”
Herlihy 2011, p.41
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9. Mitosis … continued
In mitosis, the exact copy of genetic
information, stored within the
chromosomes, must be passed from the
mother cell to the two daughter cells.
Herlihy 2011, p.41
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10. Meiosis
Meiosis occurs only in sex cells and is a special kind
of cell division
See:
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_
works.html
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11. Back to Mitosis and the Cell Cycle
The cell cycle is the sequence of events that the cell
goes through from one mitotic division to the next
biology.clc.uc.edu
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12. The Cell Cycle
The Cell Cycle is divided into two (2) major
phases
1. Interphase
2. Mitosis
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13. Interphase
During this time the cell carries on with its normal
functions and gets ready for mitosis through
growth and DNA replication
Interphase has three (3) parts to it
1. First gap phase (G1)
2. Phase S
3. Second gap phase (G2)
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14. FIRST GAP PHASE (G1)
The cell carries on it normal activities and
begins to make DNA and other substances
necessary for cell division
apbio82007.blogspot.com
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15. PHASE (S)
During Phase (S) the cell duplicates its
chromosomes and makes enough DNA for
two (2) identical cells
zebrafish.umdnj.edu
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16. SECOND GAP PHASE (G2)
This phase is the final preparatory phase for
cell division (mitosis)
It includes the synthesis of enzymes and other
protein needed for mitosis
At the completion of G2 the cell enters into the
mitotic (M) phase
Herlihy 2011, p.41
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17. MITOSIS
(M Phase)
During M Phase the cell divides into two (2) cells in
such a way that the nuclei of both cells contain
identical genetic information
Herlihy 2011, p.41
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18. Mitosis has four (4) phases:
1.
2.
3.
4.
Prophase
Metaphase
Anaphase
Telophase
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.h
tml
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19. What Next?
At the end of mitosis the daughter cells have a
choice of two pathways:
1. Enter G1 and repeat the cycle and divide again
2. Enter G-zero (G0) and ‘drop out’ of the
cell cycle and rest; they do not
undergo mitosis.
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20. HOW LONG CAN CELLS ‘REST’ FOR?
Cells may re-enter the cell cycle after days, weeks or
even years
Cancer cells do not appear to be able to stop ‘cycling’
or enter the G0 phase
Cancer cells constantly divide and proliferate
Herlihy 2011, p.42
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21. TREATING CANCER
Anti-cancer drugs work more successfully on cells
that are ‘cycling’ rather than ones that are ‘resting’
in the G0 phase
Tumours that contain many cycling cells respond
best to chemotherapy
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22. ANTI CANCER DRUGS
Anticancer drugs are classified according to the cell
cycle phase they affect
Some anti-cancer drugs are called cell cycle-phase
specific
These drugs affect cells when they are in a
particular phase
Herlihy 2011, p.42
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23. For Example
The anti-cancer drug methotrexate is cell cycle S phase
specific
Some drugs work in the M phase or in the G2 phase
Other anti-cancer drugs can work in any phase of the
cell cycle and are called cell cycle-phase non specific
http://www.oncolink.org/treatment/section.cfm?c=9&s=70
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24. CELL DIFFERENTIATION
Mitosis ensures that when one cell divides it
produces two (2) identical cells
An embryo begins life as a single cell, the fertilised
ovum, and through mitosis the single cell divides
many more times into identical cells
Herlihy 2011, p.42
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25. Sometime during their development the cells
begin to specialise, or differentiate
One cell may switch on enzymes that make red
blood cells while another cell may make bone
cells
We all begin life as one cell and end up as
billions of specialised cells
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26. When differentiation goes wrong!
When a sample of tissue (a biopsy) is
surgically removed for examination it may
show many poorly differentiated cells
This means that the cells have failed to
differentiate or specialise.
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27. For example un-differentiated cells found in a
liver tumour do not resemble normal liver cells
Failure to differentiate is characteristic of cancer
cells
Herlihy 2011, p.42
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28. BLADDER CANCER
bjui.org
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29. STEM CELLS
Stem cells are relatively un-differentiated or unspecialised cells and their job is to produce additional
un-specialised cells
Every time a stem cell divides one of the daughter cells
differentiates while the other daughter cell prepares for
further stem cell division
The rate of stem cell division varies with the tissue type
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30. For Example
Stem cells in the bone marrow and skin are
capable of dividing more than once a day, but
adult cartilage stem cells may remain inactive for
years.
With ongoing ethical research there may be the
potential here to replace damaged body
components, like the spinal cord for example.
Herlihy 2011, p.43
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31. ORDER & DISORDER
Most cell growth is orderly, but sometimes this
process becomes disorderly and un-controlled
When too many cells are produced a lump or a
tumour forms.
Tumours are either benign (not cancerous) or
malignant (cancerous).
Herlihy 2011, p.43
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32. Malignant Breast Tumour
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33. Benign Breast Tumour (mammogram)
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34. PROGRAMMED CELL DEATH
This process is known as apoptosis and is
essentially cell suicide
Apoptosis helps ride the body of old, unnecessary and unhealthy cells.
The body produces a million cells per second
the elimination of some cells by apoptosis is
necessary
Herlihy 2011, p.43
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35. Apoptosis can become uncontrolled and this
results in excessive cellular death and disease
apoptosis-networks.eu
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36. When cancer cells spread they are said to
metastasise
Sometimes cells are so badly injured that they die
or necrose.
Herlihy 2011, p.44
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37. REFERENCE
Herlihy, B. (2011) The Human Body in Health and Illness, 4th
Edition, Elsevier Saunders
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