1. Regulating the Cell Cycle & Cancer
Chapter 8

2. 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

3. 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)

4. Cell Cycle Control System
G1 checkpoint: will this cell be dividing?
Yes (growth factor) = Continue the cell cycle (green light)
No = leave the cell cycle G0 (brain and muscle)
G2 checkpoint: is everything ready for mitosis?
Yes (mitosis promoting factor) = mitosis
M (metaphase) checkpoint: are all sister chromatids ready for separation?
Yes = anaphase

5. 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)
No density dependent inhibition (in vivo and vitro)
No anchorage dependence (in vitro)
No dependence on growth factors
Cancer cells appear to be immortal (no cell cycle limit)

6. 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)

7. 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)

8. 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:
Preventing cell division until DNA is repaired
Cell suicide
All genes are inherited