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 G 0 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 REGULATORS EXTERNAL Growth factors

EXTERNAL SIGNALS ________ 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. 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 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. 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 the chromosomes have been copied OTHER REGULATORS INTERNAL

In early 1980’s scientists discovered a protein in dividing cells that caused a ______________to form in _______________ cells INTERNAL REGULATORS Mitotic spindle NON-dividing

Levels of this protein rose and fell with the cell cycle so it was named _________ because it seemed to control the cell cycle. A whole family of CYCLINS have since been discovered that regulate the _____________________ in EUKARYOTIC CELLS INTERNAL REGULATORS CYCLIN TIMING of CELL CYCLE

Slide from Kim Foglia

Slide from Kim Foglia

_____________ 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 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 Nobel Prize Physiology/Medicine Discovery of Telomeres

Cancer cells have lost control of their cell division genes CHO (Chinese Hamster Ovary) cells in culture SEM Image by: Riedell

Cancer cells Cancer 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 G 1 checkpoint –Starts apoptosis of damaged cells CELL CYCLE p53

Slide from Kim Foglia

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. 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 Differently TedED: How Cancer Cells Behave Differently

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