Transcript Some cells divide occasionally

REGULATING
the
CELL CYCLE
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)
What controls the cell cycle?
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How does a cell know it’s time to divide?
What signals a G0 cell to return to cycle?
Where do signals come from?
What happens when cells
don’t respond to signals?
CELL CYCLE REGULATORS
EXTERNAL
______________
REGULATORS
•Proteins that respond to events outside the cell.
•Signals tell cell to speed/slow down cell cycle
EX:
Growth factors
______________________
•stimulate cells to divide
•important during wound healing
and embryo development
EXTERNAL SIGNALS
________
INJURY
Cell division genes
in cells near injury
TURN ON to heal and
replace damaged/missing cells
and TURN OFF when the
repair has been made.
Control of Cell Division
Cells receive signals from neighbors
Section 10-3
If center cells are removed,
cells near the space will
start to grow again.
Cells grow until they
touch other cells
SHOWS: Cell division
genes can be turned on
and off
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.
GROWTH FACTORS
CONTACT INHIBITION
___________________________________
Crowded cells stop dividing
ANCHORAGE DEPENDENCE
______________________________
Cells must be attached in order to divide
OTHER REGULATORS
INTERNAL
______________
REGULATORS
•Proteins respond to events inside the cell.
•Cell cycle proceeds only if certain processes
have happened
EX: Cell can’t enter mitosis until all the
chromosomes have been copied
INTERNAL REGULATORS
In early 1980’s scientists discovered a
protein in dividing cells that caused a
Mitotic spindle
______________to
form in
NON-dividing cells
_______________
INTERNAL 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
Slide from Kim Foglia
http://www.explorebiology.com
Slide from Kim Foglia
http://www.explorebiology.com
TELOMERES
_____________
• Protective ends on all chromosomes
• Protect DNA code from being lost
• Become shorter with each replication;
• Older cells have shorter telomeres
Most cells divide 20-50 times in culture;
then stop, age, die
Dolly the cloned sheep died
of “old age” at 6½
Cancer cells are “immortal” HeLa cells from a tumor removed from a
woman (Henrietta Lacks) in 1951 are still
reproducing in culture
Telomerase =
enzyme that lengthens telomeres
Cancer cells are “immortal”
– have increased
telomerase activity
2009
Nobel Prize
Physiology/Medicine
Discovery of Telomeres
Jack Szostak
Carol Greider Elizabeth Blackburn.
Cancer cells have lost control
of their cell division genes
SEM Image by: Riedell
CHO (Chinese Hamster Ovary) cells in culture
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
p53 .
tumor suppressor gene called ____
– Signals DNA repair enzymes
– Holds cell at G1 checkpoint
– Starts apoptosis of damaged cells
Slide from Kim Foglia
http://www.explorebiology.com
NO CONTACT INHIBITION
Cancer cells lose
contact inhibition
They don’t stop dividing
when they touch nearby
cells. . .
they just keep growing!
That’s what makes
a tumor.
Contact
Inhibition
VIDEO
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CANCER CELLS
Don’t respond to control signals
Lose contact inhibition
Lose anchorage dependence
Telomerase enzymes maintain/replace
telomeres
Transformation
________________
process that changes
a normal cell into
a cancer cell
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Cancer cells
Don’t stop dividing
Like a “car with no brakes”
METASTASIS
_________________
Can spread to new places
Carcinogens are substances that can
• ______________
damage DNA and cause cancer
Cigarette smoke (or chew), UV radiation,
radiation, chemicals, pollution, genetics,
viruses (HPV)
TedED: How Cancer Cells Behave Differently
ANTI-SMOKING commercial