Regulating the Cell Cycle & Cancer Chapter 8

Regulating Cell Division Multicellular organisms must regulate cell division –Constantly replace skin and digestive cells –Brain cells (neurons) should not divide –Liver cells only divide to repair damage Mechanisms of control: Anchorage dependence: cells need to be anchored to other cells Density-dependent inhibition: cells stop growing when there is no room to grow Growth factor: protein that stimulates cell growth

Cell Cycle Control System Checkpoints are crucial places where the cell cycle stops (red stop light): Each checkpoint needs to be overridden by the specific go ahead signals for this phase (green light)

Cell Cycle Control System G 1 checkpoint: will this cell be dividing? –Yes (growth factor) = Continue the cell cycle (green light) –No = leave the cell cycle G 0 (brain and muscle) G 2 checkpoint: is everything ready for mitosis? –Yes (mitosis promoting factor) = mitosis M (metaphase) checkpoint: are all sister chromatids ready for separation? –Yes = anaphase

Cancer Cells Cancer cells have numerous mutations (cumulative mutations increase with age) in the genes that code for checkpoint protein machinery They escape the normal cell cycle control mechanisms (run the stop lights) a.No density dependent inhibition (in vivo and vitro) b.No anchorage dependence (in vitro) c.No dependence on growth factors d.Cancer cells appear to be immortal (no cell cycle limit)

Cancer Cells If cells become abnormal they are located by the immune system and destroyed If they evade recognition they will start forming tumors Benign tumors –Cells stay at original location –Slow proliferation Malignant tumors –Can spread to other areas (metastasis)

Malignant Tumors Can differ in: # of chromosomes, metabolic rate, abnormal cell surfaces, and large nuclei Names include: carcinoma, sarcoma, leukemia, and lymphoma There are 4 levels of malignancy for cancer cells indicating how aggressive/mutated the cell is with level 1 being the least and level 4 being the most aggressive type of cancer Viruses can cause cancer (HPV & cervical cancer) There is a genetic predisposition for cancer (it’s hereditary)

Cancer = Hereditary Proto-oncogenes help regulate the cell cycle and facilitate cell-cell communication –When to divide –Cell recognition (signal transduction) Mutated proto-oncogenes are called oncogenes are tumor-promoting Oncogenes are found in most cancer cells found in malignant tumors Tumor-suppressing genes help keep cancers from developing in two ways: 1.Preventing cell division until DNA is repaired 2.Cell suicide All genes are inherited