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?• 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

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

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

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

Slide from Kim Foglia http://www.explorebiology.com

Slide from Kim Foglia http://www.explorebiology.com

_____________ • Protective ends on all chromosomes• Protect DNA code from being lost• Become shorter with each replication;• Older cells have shorter telomeres

TELOMERES

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

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 manycauses, but all cancers have one thing incommon 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 Fogliahttp://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

Contact Inhibition VIDEO

CANCER CELLS• Don’t respond to control signals• Lose contact inhibition• Lose anchorage dependence• Telomerase enzymes

maintain/replace telomeres

________________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 cancer Cigarette smoke (or chew), UV radiation, radiation, chemicals, pollution, genetics,

viruses (HPV)

Carcinogens

METASTASIS

TedED: How Cancer Cells Behave TedED: How Cancer Cells Behave Differently Differently

ANTI-SMOKING commercial