1. 10-3: Regulating the cell cycle

2. Cardiac cells Small intestine Smooth muscle Nerve cell: brain Cardiac: cannot divide Smooth muscle: can divide Intestine: 1-2 days, can divide Nerve cell: cannot divide RBC: 120 days, cannot divide Red blood cell Specialized cells divide at different rates Some cells never divide

3. Controls on cell division ► Not all cells in the body divide at the same rate ► Cells in a petri dish will divide until they fill the dish, then they stop. ► If cells are removed, they’ll grow until the space is filled again. ► Controls on cell division can be turned on and off.

4. Cell cycle regulators ► The protein cyclin regulates the timing of the cell cycle in eukaryotic cells. When present, cyclin triggers cell division.

5. Internal regulators ► Proteins that respond to internal events in the cell. ► Some make sure that the cell doesn’t enter mitosis until the DNA is replicated ► Another makes sure that chromosomes are attached to the spindle before anaphase. Different cyclins active at phases of the cell cycle

6. External regulators ► Proteins that respond to events outside the cell. ► Direct the cell to speed up or slow down the cell cycle. ► Growth regulators: important in embryos, for healing wounds Rubber bullet wound Cat embryo

7. Inhibitors on cell surfaces cause cells to slow or stop division

8. Uncontrolled cell growth ► Cancer is a disease of the cell cycle ► Cancer cells don’t respond to the signals that regulate growth. ► Leads to uncontrolled cell growth. ► Causes: viruses, tobacco, radiation exposure ► Form masses of cells: tumors Oral cancer Melanoma: skin cancer

9. Stem cells ► Unspecialized cells that have the ability to turn into any kind of cell. ► Could replace damaged cells of brain, nervous system. Human stem cell

10. stem cell controversy stem cell controversy ► Stem cells are produced from human embryos, and are destroyed when used for research ► Raises moral and ethical questions as to their use: Is a fertilized egg a human being? Stem cells in umbilical cord blood Human blastocyte: 100 cells

11. Adult stem cells ► Adult stem cells are found in bone marrow ► Future possibility: a person’s own stem cells could be used to heal previously untreatable conditions: spinal cord injury, grow new liver tissue, replace heart valves, reverse the effects of diabetes.