Post on 18-Apr-2020
REGULATING the
CELL CYCLE
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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?• 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?
______________ REGULATORS
• Proteins that respond to events outside the cell. • Signals tell cell to speed/slow down cell cycle
EX: ______________________• stimulate cells to divide• important during wound healing
and embryo development
CELL CYCLE REGULATORSEXTERNAL
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Growth factors
EXTERNAL SIGNALS
________
Cell division genes in cells near injuryTURN ON to heal and replace damaged/missing cells and TURN OFF when the repair has been made.
INJURY
Control of Cell Division
Section 10-3
Cells grow until they touch other cells
If center cells are removed,cells near the space will start to grow again.
SHOWS: Cell division genes can be turned on and off
Cells receive signals from neighbors
Molecules on the surface of neighboringcells act as signals to slow down or stop thecell’s cycle.
These signals preventexcessive growth andkeep tissues from disrupting each other.
EXTERNAL REGULATORS
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GROWTH FACTORS
___________________________________
Crowded cells stop dividing
______________________________
Cells must be attached in order to divide
CONTACT INHIBITION
ANCHORAGE DEPENDENCE
______________ 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 thechromosomes have been copied
OTHER REGULATORSINTERNAL
In early 1980’s scientists discovered aprotein in dividing cells that caused a ______________to form in
_______________ cells
INTERNAL REGULATORS
Mitotic spindleNON-dividing
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Levels of this protein rose and fell withthe cell cycle so it was named_________ because it seemed tocontrol the cell cycle.
A whole family ofCYCLINS have since beendiscovered that regulate the_____________________in EUKARYOTIC CELLS
INTERNAL REGULATORS
CYCLIN
TIMING of CELL CYCLE
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_____________
• Protective ends on all chromosomes
• Protect DNA code from being lost
• Become shorter with each replication;
• Older cells have shorter telomeres
TELOMERES
http://www.instablogsimages.com/images/2009/12/12/barrow_uV86b_16105.jpg
http://www.eliteskin.com/img/telomere_chromosome.jpg
Most cells divide 20-50 times in culture; then stop, age, die
Cancer cells are “immortal” -HeLa cells from a tumor removed from a woman (Henrietta Lacks) in 1951 are still reproducing in culture
http://www.sanger.ac.uk/Info/Press/gfx/081223_cells_300.jpg
http://i.telegraph.co.uk/telegraph/multimedia/archive/01691/cloned-sheep_1691358c.jpg
Dolly the cloned sheep died of “old age” at 6½
Telomerase = enzyme that lengthens telomeres
Cancer cells are “immortal”– have increased
telomerase activity
Jack Szostak Carol Greider Elizabeth Blackburn.
2009Nobel PrizePhysiology/MedicineDiscovery of Telomeres
Cancer cells have lost control of their cell division genes
CHO (Chinese Hamster Ovary) cells in culture
SEM Image by: Riedell
Cancer cellsCancer is complicated and can have many
causes, but all cancers have one thing in
common they have lost control over their _____________.
Many cancers cells have a damaged or defective
tumor suppressor gene called ____ .
– Signals DNA repair enzymes
– Holds cell at G1 checkpoint
– Starts apoptosis of damaged cells
CELL CYCLE
p53
Slide from Kim Foglia
http://www.explorebiology.com
Cancer cells losecontact inhibition
They don’t stop dividingwhen they touch nearbycells. . .they just keep growing!
That’s what makesa tumor.
NO CONTACT INHIBITION
http://www.exn.ca/news/images/2000/08/02/20000802-cancer.jpg
See a video
Slide from Kim Foglia
http://www.explorebiology.com
CANCER CELLS• Don’t respond to control signals
• Lose contact inhibition
• Lose anchorage dependence
• Telomerase enzymes maintain/replacetelomeres
________________
process that changes
a normal cell into
a cancer cell
Transformation
Cancer cells• Don’t stop dividing
• Like a “car with no brakes”
• _________________Can spread to new places
• ______________ are substances that can damage DNA and cause cancerCigarette smoke (or chew), UV radiation, radiation, chemicals, pollution, genetics, viruses (HPV)
Carcinogens
http://www.dfci.harvard.edu/abo/news/publications/pop/fall-winter-2004/images/metastasis_1.jpg
METASTASIS
Slide from Kim Foglia
http://www.explorebiology.com
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