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Cell division is highly
regulated. The cell
does not divide
unless it receives the
appropriate
extracellular signals.
Growth factors
(hormones or
polypeptides)
stimulate growth.
Cells also have
proteins which come
in contact with other
cells. If the contact is
lost, cell division is
stimulated.
There are a variety of ways to
stimulate cell growth. One is for
a growth factor to bind to
receptors on the cell membrane
(extracellular signaling), which
triggers a series of events
leading to cell division.
A second type of signaling is
called intracellular signaling.
Cells grow until they are in
contact with cells around them.
When they touch, cell adhesion
proteins attach the two cells.
These adhesion proteins are
transmembrane proteins which
transmit a signal to stop growing
when they contact another cell.
If the neighboring cell dies or is
destroyed by injury, the
adhesion protein sends a signal
to initiate growth and replace the
lost cell.
Growth hormones have a
specific shape and fit like a
key only inside receptors
which have the exact shape
necessary. Because of this,
hormones can be released
from a distant location (like
the brain) into the blood, and
travel all over the body but
only initiate growth of the
desired cells. Small
polypeptides can be released
from cells into the
extracellular fluid and
stimulate growth locally.
•Receptors are
transmembrane proteins,
with the binding site on
the extracellular surface.
•When the hormone
binds, the receptor
changes shape,
activating an enzyme
located in the
intracellular portion of the
cell. Thus, the receptor
converts a signal on the
outside into a signal on
the inside.
•The receptor enzyme
will add a phosphate
group onto a specific
protein, activating that
protein.
•There are a number of
pathways which are involved
in activating
(phosphorylating) or
inactivating
(dephosphorylating) proteins.
This gives the cell many
ways of controlling what is
going on inside.
•One such pathway involves
phospholipids which, when
changed, alter the activity of
specific proteins.
•A kinase is an enzyme
which phosphorylates
molecules.
•Growth and cell
division have to be
closely regulated.
Therefore, there are
many proteins involved
in carrying the signal
from the receptor to the
nucleus where the
genes regulating cell
division can be
activated. These
proteins are called
proto-oncogenes.
•The proto-oncogenes
work in a specific
sequence. When one is
activated, it then
activates the next one in
line.
•Each proto-oncogene
is a site of regulation
•Finally, a proto-oncogene is activated and now can
enter the nucleus. This protein will bind to the DNA
in the promoter site of a specific gene or a group of
genes. When this occurs, the gene will be
transcribed.
There is a second set of proteins
known as tumor suppressors.
These proteins function by
inactivating (turning off) the
proto-oncogenes. In essence,
they are necessary to stop cell
division.
These proteins were discovered
by scientists studying cancer.
They found that when the genes
for these proteins were activated,
tumors did not develop when
they gave mice carcinogens.
That is, they suppressed tumor
formation.
Tumor Suppressor
Activity
Similar to proto-oncogenes,
there are a number of
tumor suppressors. Each
tumor suppressor protein
inactivates specific protooncogenes. By doing so,
they shut off the signal
which causes cells to
divide.
Tumor Suppressor Pathway
Proto-oncogenes are
normal and necessary
proteins. If one of these
genes &, therefore,
proteins is mutated, it can
become an oncogene
(and cause cancer).
How? When a protooncogene becomes
activated, it will now
modify & activate the next
proto-oncogene in the
sequence. All
downstream proteins now
become activated and cell
division results. If the
mutation results in a
permanently activated
proto-oncogene, it causes
uncontrolled cell growth.
Liver Cancer
Colon Cancer
Lung Cancer
As cancer cells continuously grow, they crowd out normal cells around them.
Blood vessels are squeezed, shutting down the flow of oxygen and nutrients.
Normal cells are killed. Cancer cells are able to survive, because they cause the
growth of blood vessels feeding the cancer cells themselves. A new type of drug
to treat cancer actually prevents the growth of these cancer-supplying blood
vessels.
Skin Cancer
Colon Cancer
Skin Cancer
NEWS FLASH
We have a natural defense
against cancerous cells. It
is our immune cells.
Cancer cells often express
abnormal proteins. These
proteins are detected as
foreign proteins and the
cells are destroyed. In the
picture, the tumor cell is
killed by a T lymphocyte
(white blood cell) which
inserts a protein pore
which allows cytoplasm to
leak out, killing the cell.
REVIEW OF CELL GROWTH REGULATORY MECANISMS AND
POSSIBLE WAYS THIS REGULATION IS LOST
http://www.revolutionhealth.com/conditions/cancer/skin-cancermelanoma/?s_kwcid=ContentNetwork|853876134
Video of skin cancer metastisis
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