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Knowing When to Stop
Suppose you had a paper cut on your finger. Although the
cut may have bled and stung a little, after a few days, it will
have disappeared, and your finger would be as good as
new.
1. How do you think the body repairs an injury, such as a cut on a
finger?
The cut is repaired by the production of new cells through cell division.
2. How long do you think this repair process continues?
Cell division continues until the cut is repaired.
3. What do you think causes the cells to stop the repair process?
Students will likely say that when the cut is filled in, there is no
room for more cells to grow.
REGULATING
the
CELL CYCLE (8-3)
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Section Outline
Section 10-3
Regulating the Cell Cycle
A. Controls on Cell Division
B. Cell Cycle Regulators
1. Internal Regulators
2. External Regulators
C. Uncontrolled Cell Growth
Go to
Section:
Control of Cell Division
Section 10-3
If center cells are removed,
cells near the space will
start to grow again.
Cells grow until they
touch other cells
Go to
Section:
SHOWS: Cell division
genes can be turned on
and off
CELL DIVISION GENES
EXAMPLE: Cell division genes can be
turned on in case of injury.
________
Cells near injury are
stimulated to divide
to heal and replace
damaged/missing cells
and shut off when the
repair has been made.
CELL DIVISION GENES
Some cells divide frequently
(some human skin cells divide once/hour)
Some cells divide occasionally
(liver cells divide about once/year)
Some cells don’t divide once they form
(nerve cells)
CELL CYCLE REGULATORS
In early 1980’s scientists discovered a
protein in dividing cells that caused a
Mitotic spindle
______________to
form in
NON-dividing
_______________
cells
Pearson Education Inc; Publishing as Pearson Prentice Hall
CELL CYCLE REGULATORS
Levels of this protein rose and fell with
the cell cycle so it was named
__________
CYCLIN because it seemed to
control the cell cycle.
A whole family of
CYCLINS have since been
discovered that regulate the
TIMING of CELL CYCLE
_____________________
in EUKARYOTIC CELLS
Pearson Education Inc; Publishing as Pearson Prentice Hall
OTHER REGULATORS
INTERNAL
______________
REGULATORS
Proteins that respond to events inside
the cell.
Allow cell cycle to proceed only if
certain processes have happened
EX: Cell can’t enter mitosis until all the
chromosomes have been copied
OTHER REGULATORS
EXTERNAL
______________
REGULATORS
Proteins that respond to events outside
the cell.
Signals tell cell to speed up or slow
down the cell cycle
EX:
Growth factors stimulate cells to divide
Especially important during
wound healing and
embryo development
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EXTERNAL REGULATORS
Molecules on the surface of neighboring
cells act as signals to slow down
or stop the
cell’s cycle.
These signals prevent
excessive growth and
keep tissues from
disrupting each other.
Pearson Education Inc; Publishing as Pearson Prentice Hall
Cancer cells have lost control
of their cell division genes
SEM Image by: Riedell
CHO (Chinese Hamster Ovary) cells in culture
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Cancer cells don’t stop
when they touch nearby
cells. . .
they just keep growing!
That’s what makes
a tumor.
http://www.exn.ca/news/images/2000/08/02/20000802-cancer.jpg
Cancer cells
• Don’t stop dividing
• Like a “car with no brakes”
• Can spread to new places
(METASTASIS)
• ______________
Carcinogens are substances that
can damage DNA and cause cancer
Ex: Cigarette smoke (OR CHEW),
Radiation, chemicals in environment,
even viruses,
http://www.dfci.harvard.edu/abo/news/publications/pop/fall-winter-2004/images/metastasis_1.jpg
Cancer cells
Cancer is complicated and can have many
causes, but all cancers have one thing in
common . . .…
They have lost control over their
_____________.
CELL CYCLE
Many cancers cells have a damaged or defective
gene called p53
_____, so they can’t respond to
normal cell signals to control their growth.
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