REGULATING the CELL CYCLE.

Transcription

1 REGULATING the CELL CYCLE

2 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)

3 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?

4 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

5 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.

6 Section 10-3 Control of Cell Division Cells receive signals from neighbors 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

7 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. Pearson Education Inc; Publishing as Pearson Prentice Hall

8 GROWTH FACTORS CONTACT INHIBITION Crowded cells stop dividing ANCHORAGE DEPENDENCE Cells must be attached in order to divide

9 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

10 INTERNAL REGULATORS In early 1980 s scientists discovered a protein in dividing cells that caused a to Mitotic spindle form in NON-dividing cells Pearson Education Inc; Publishing as Pearson Prentice Hall

11 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 Pearson Education Inc; Publishing as Pearson Prentice Hall

12 Slide from Kim Foglia

13 Slide from Kim Foglia

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

15 Most cells divide 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

16 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.

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

18 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 G 1 checkpoint Starts apoptosis of damaged cells

19 Slide from Kim Foglia

20 NO CONTACT INHIBITION Cancer cells lose contact inhibition See a video They don t stop dividing when they touch nearby cells... they just keep growing! That s what makes a tumor.

21 Slide from Kim Foglia

22 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

23 Don t stop dividing Cancer cells 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)

24 Slide from Kim Foglia

25 ANTI-SMOKING commercial