1. Fun Fact! There are over 200 different types of cells in the human body, each performing specific functions! – Nerve cells, eye cells, cardiac cells, etc. Do all types of cells go through the cell cycle at the same rate? NO! Some cells divide quickly & some divide slowly. Some types of cells do not undergo cell division at all!

2. Different cell types divide at different rates! Muscle & nerve cells do not divide once they have developed. – Has anyone ever told you that once you kill your brain cells, you don’t get them back? Skin cells & cells in the bone marrow divide rapidly.

3. Regulating the Cell Cycle

4. Control of Cell Division Cell growth & cell division can be turned on & off. When you’re injured, your cells divide rapidly to repair the injury. When the injury has healed, the cells stop dividing.

5. Regulation of the Cell Cycle Controlling the cell cycle is necessary for healthy growth. Internal & external factors regulate cell division. – External factors include physical & chemical signals. – Internal factors include proteins that control cell division.

6. For example… Apoptosis is programmed cell death, or “cell suicide”. – A normal feature of healthy organisms – Caused by a cell’s production of self-destructive enzymes Webbing of the fingers & toes is normal in developing infants. Before the baby is born, apoptosis occurs & enzymes destroy the extra tissues between the fingers.

7. Uncontrolled Cell Growth What happens when your cells lose control & cannot regulate their cell cycle? When cells in your body cannot control cell growth & division, cancer may form. Cancer cells cannot respond to the signals that regulate the division of cells.

8. Uncontrolled Cell Growth When cancer cells have been dividing uncontrollably, tumors form. Tumors can damage surrounding tissue. Cells from tumors can break free & travel to other parts of the body, forming new tumors.

11. Uncontrolled Cell Growth Most mammal cells form a single layer in a culture dish & stop dividing once they touch other cells. Cancer cells do not carry out necessary functions. They come from normal cells with damage to genes involved in cell cycle regulation.

12. Carcinogens Substances known to promote cancer Some reasons that cells may lose the ability to control growth: – Smoking – Radiation Exposure – Viral Infection Scientists who study cancer research how cells divide.

13. Treatment There are several methods of treating cancer. Standard cancer treatments typically kill both cancerous cells & healthy cells. – This is why there are so many side effects.