1. Regulating the Cell Cycle 10-3

2. Controls on Cell Division If we look at cells dividing in a petri dish we can see that they will divide until they cover the bottom of the dish

3. Controls on Cell Division If we take out all of the cells in the middle of the dish, the other cells will divide until the plate is covered again, at which point cell division will stop occuring

4. Controls on Cell Division This is similar to how the body heals When the body is cut, broken, or bruised, cells at the edge of the injury are stimulated to divide rapidly

5. Controls on Cell Division This stimulation is what creates the healing of the injury and restoration of the body

6. Cell Cycle Regulators In the 1980’s two scientists, Tim Hunt of the UK and Mark Kirschner of the USA discovered that cells in mitosis contain a specific protein that stimulates Mitosis to occur

7. Cell Cycle Regulators This protein is called Cyclin because it controls the cell cycle They did an experiment where they injected cyclin which was found to stimulate the growth of spindles, causing mitosis to occur

8. Cyclin There are many different types of Cyclin proteins that are found in mitotic cells Some are known as internal regulators while others are external regulators

9. Internal Regulators Cyclin proteins that are internal regulators respond to events that are inside the cell Examples would be cyclin that prevents a cell from entering anaphase until all its chromosomes are attached to spindles

10. External Regulators External Regulators are cyclin proteins that respond to events that are outside the cell They direct cells to speed up or slow down the cell cycle

11. Cancer Cell growth and reproduction must be monitored carefully If it is uncontrolled, cancer will form Cancer cells do not respond to the signals that regulate most cells

12. Cancer When a cancer replicates uncontrollably it will form a tumor which can harm surrounding tissue