Download The Cell Cycle and Cancer

The Cell Cycle and Cancer
Cell signaling: chemical
communication between cells
Chemical signals outside of the cell
trigger a cascade of signals that tell a
cell when it is time to divide. Cell
Signaling Animation
Cancer
• Normal cell division:
– Controlled by cell cycle checkpoints
• CHECKPOINTS – critical control points that determine if a
cell will move to the next portion of the cell cycle.
• Cancerous cell division:
– Ignores the cell cycle checkpoints
•
•
•
•
Caused by DNA mutations
Cells grow and divide out of control
Cancerous cells do not perform designated purpose.
Crowd out normal cells that do perform designated purpose.
Cell Cycle Checkpoints
There are several factors that regulate the cell
cycle and assure a cell divides correctly.
• G1/S
– Monitors cell size and for DNA damage
• G2/M
– Replication complete, DNA damage?
• M
– Chromosomes aligned?
Control of Cellular Division
– Genes code for proteins that either stimulate
cell growth or suppress it.
• Cyclins: proteins that control phases of the cell
cycle.
– Examples:
» S-cycline stimulates DNA replication
» M-cycline helps trigger mitosis
• Proto-oncogenes: genes involved in growth
stimulation
– Mutation here can produce an “onco-gene” which triggers
uncontrolled growth. GAS PEDAL
• Tumor suppressor genes: inhibit growth and
division
– Mutation here = loss of inhibition BRAKE
» Cells divide out of control without normal functioning
suppressor gene
• When proto-oncogenes
and tumor suppressor
genes are mutated the
cell can trigger cell
death, called apoptosis
– An example of a tumor
suppressor gene:
• p53 gene codes for
apoptosis:
(Programmed cell
death)
2. Chemical Signals tell a cell when to start
and stop dividing.
(Target cells animation: click on go sign)
Control of cell division continued:
Density Dependent Inhibition: Normal cells cease
dividing once critical cell density is reached.
Cancer cells do not possess this trait.
Neighboring cells communicate with dividing
cells to regulate growth.
(Normal contact inhibition animation: click on petri dish)
DNA mutations disrupt the cell cycle.
Carcinogens (anything
that can cause cancer):
1. radiation
2. smoking
3. Pollutants
4. chemicals
5. viruses
6. Heredity
Multistep Process:
Cancer results from “multiple hits”
• Cancer requires mutation of multiple genes
• Age relationship:
– Cancer rate increases dramatically with age.
• Delay between carcinogen exposure and
onset
– 5-8 year delay between carcinogen exposure
(Hiroshima and Nagasaki) and onset of
leukemia
– 15 year delay between tuberculosis X-ray
treatment and onset of breast cancer
Age and Cancer
Cancer is a disease of the cell cycle. Some
of the body’s cells divide uncontrollably and
tumors form.
Tumors in Liver
Tumor in Colon
While normal cells will stop dividing if there is a mutation in
the DNA, cancer cells will continue to divide with mutation.
Due to DNA mutations, cancer cells ignore the
chemical signals that start and stop the cell cycle.
They don’t communicate with neighboring cells
and continue to grow and form tumors.
2 animations of cancer cells dividing: click on picture
Benign or malignant?
• Benign tumors do
not spread from their
site of origin, but can
crowd out
surrounding cells.
• Malignant tumors
can spread from the
original site and
cause secondary
tumors. This is called
metastasis.
• Metastasis: cells travel
through blood vessels or
lymph to other areas of the
body and grow there. This
is what makes tumors so
lethal.
Pathways of cancer:
cell signaling
• interfere with normal
functioning of other tissues
vital to survival.
.
Cancer therapies
• Classic cancer therapies target rapidly
dividing cells
– Radiation
– Chemotherapy
– Surgery
• Side effects
– Hair loss
– Weakened immune system
– Digestive tract issues
Cancer therapies
• Immune system may not target tumor
cells because they appear to be “self”
• Some therapies activate one's immune
system against a cancer
SUMMARY
Normal Cell Division
1. DNA is replicated
properly.
2. Chemical checkpoints
signal start and stop
of the cell cycle.
3. Cells communicate
with each other so
they don’t become
overcrowded.
Cancer Cells
1. Mutations occur in the DNA
2. Cell ignores normal
checkpoints = excessive
division
3. Mutated cells can spread by
traveling through blood
vessels to new locations in
the body