Interest Grabber Answers Knowing When to Stop Suppose you had a paper cut on your finger. Although the cut may have bled and stung a little, after a few days, it will have disappeared, and your finger would be as good as new. 1. How do you think the body repairs an injury, such as a cut on a finger? The cut is repaired by the production of new cells through cell division. 2. How long do you think this repair process continues? Cell division continues until the cut is repaired. 3. What do you think causes the cells to stop the repair process? Students will likely say that when the cut is filled in, there is no room for more cells to grow.
REGULATING the CELL CYCLE
Control of Cell Division 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 Go to Section:
CELL DIVISION GENES EXAMPLE: Cell division genes can be turned on in case of injury. Cells near injury are stimulated to divide to heal and replace damaged/missing cells and shut off when the repair has been made.
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)
CELL CYCLE REGULATORS In early 1980 s scientists discovered a protein in dividing cells that caused a to Mitotic spindle form in NON-dividing cells
CELL CYCLE 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
OTHER REGULATORS INTERNAL REGULATORS Proteins that respond to events inside the cell. Allow cell cycle to proceed only if certain processes have happened EX: Cell can t enter mitosis until all the chromosomes have been copied
Three Cell Cycle Checkpoints 1 st checkpoint: at the end of G1 (checks that the cell has doubled in size) 2 nd checkpoint: at the end of G2 (checks that the cell can divide) 3 rd checkpoint: at the end of metaphase (checks to see that replicated chromosomes are attached to spindle fibers)
OTHER REGULATORS EXTERNAL REGULATORS Proteins that respond to events outside the cell. Signals tell cell to speed up or slow down the cell cycle EX: Growth factors stimulate cells to divide Especially important during wound healing and embryo development
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.
Cancer cells have lost control of their cell division genes SEM Image by: Riedell CHO (Chinese Hamster Ovary) cells in culture
NO CONTACT INHIBITION Cancer cells don t stop when they touch nearby cells... they just keep growing! See a video That s what makes a tumor. http://www.exn.ca/news/images/2000/08/02/20000802-cancer.jpg
Don t stop dividing Cancer cells Like a car with no brakes Can spread to new places (METASTASIS) Carcinogens are substances that can damage DNA and cause cancer Ex: Cigarette smoke (OR CHEW), Radiation, chemicals in environment, even viruses,
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 gene called, so they can t respond to normal cell signals to control their growth.
He La cells http://www.npr.org/ blogs/health/2013/0 8/07/209807857/de cades-after-lacksdeath-family-getsa-say-on-her-cells