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Timing and rate of cell division in different
parts of a plant or animal are crucial to
normal growth, development and
Frequency of cell division varies with the type
of cell
Cell cycle is regulated at certain checkpoints
by both internal and external controls
Checkpoint: stop and goahead signals that regulate
the cell cycle
Three major checkpoints
are found in the G1, G2 and
M phases.
Cancer cells do not respond normally to the
body’s control mechanisms
Cancer cells are characterized by abnormal
cell division
If and when cancer cells stop dividing, they do
so at random points in the cycle, rather than
at normal checkpoints
Cancer cells are different from normal cells in
two fundamental ways:
Cancer cells divide out of control
Cancer cells can pile up on one another
 tumor – abnormal lump of cells
 benign tumor – tumor that remains in one place
in the body
 malignant tumor – tumor that is capable of
spreading throughout the body
 metastasis – spread of cancer cells from the initial
site to other parts of the body
There is a wide range of cell division rates in
different types of human cells
Related to the function of each type.
 For example, some cells, such as red blood cells,
muscle cells, and nerve cells, lose the capacity to
divide as they differentiate and mature.
Non-Cancerous Cells
Mammalian red blood cells only
 once they have matured they extrude their nuclei
and thus have no instructions for cell division.
From this moment they have 100 to 120 days to
function as oxygen (and carbon dioxide)
Most normal cells undergo 20 to 30 rounds of
cell division before carrying out programmed
Any more divisions may result in mutated
cells that might harm the organism.
Cancerous Cells
Cells that accumulate enough mutations may
lose control of cell division, leading to the
development of cancer.
Cancer cells have been found to make an
enzyme called telomerase
 signals them to continue cell division
Mutations in other cancer cells do not allow
the cells to produce or recognize proteins
which signal cell suicide.
Some treatments for cancer involve the use
of drugs that specifically attack cells that are
actively dividing.
 Why would this be effective for fighting cancerous
Read Pages 52 – 55 and:
 Provide a 2-3 point summary on the methods of
Diagnosing Cancer
 Provide a 2-3 point summary on the treatment
methods of Cancer
 Answer # 2, 3, 7, 10