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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? 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 • • • • 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 • • • 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
