Download Regulation of the Cell Cycle / Cancer

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
• 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
Cancer Cells
•
•
a.
b.
c.
d.
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)
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