1. Cell Regulation Objectives Identify a factor that can stop cells from growing Describe how the cell cycle is regulated Explain how cancer cells are different from other cells

2. I. Regulating the Cell Cycle *Not all cells move through the cell cycle at the same rate. *In the human body, most muscle and nerve cells do not divide at all once they have developed. **Cells of the skin and digestive tract, divide rapidly throughout life. Such cells may pass through a complete cycle every few hours

3. A. Controls on Cell Division **Scientist can observe the effects of controlled cell growth in the lab by placing some cells in a petri dish containing nutrient broth

4. B. Cell Cycle Regulators Cyclins regulate the timing of the cell cycle in eukaryotic cells 1. Internal regulators are proteins that respond to events inside the cell 2. External regulators are proteins that respond to events outside the cell. *They direct the cell to speed up or slow down the cell cycle *They prevent excessive cell growth and keep the tissues of the body from disrupting each other

5. C. Uncontrolled Cell Growth Cancer is a disorder in which some of the body’s own cells lose the ability to control growth *Cancer cells do not respond to signals that regulate growth *Cancer cells from masses of cells called tumors *Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities.

7. Tumor