Download Anchorage, cell density, and chemical growth factors affect cell

Anchorage, cell density, and chemical growth factors affect cell division
Animals and plants need to be able to control the
timing of the cell division in different parts of the body
in order to grow and develop normally.
EX. Cells in the digestive tract and skins cells need to
be replaced frequently to replace cells that have flaked
off. Liver cells usually do not divide unless the liver is
damaged.
-Most animal cells exhibit anchorage dependence –
they must be in contact with a solid surface to divide.
Scientist have found that cells growing on the surface
of a dish multiply to form single layer and usually stop
dividing when they tough one another (density-dependent inhibition).
If cells are removed – the cells bordering the open space begin to divide again.
Clearing a space in a dish is analogous to cutting your skin. What causes
this??? Proteins called growth factors – proteins that are secreted by certain
body cells to divide. Most cells require growth factors to start dividing and they
stop dividing when they run out of these substances.
Growth factors signal cell cycle control system
-Cells do not divide unless they are signaled by other
cells to do so. Growth factors are the main signal.
-The events of the cell cycle are directed by a distinct
cell cycle control system (it is a set of molecules in
the cell that both trigger and coordinate key events in
the cycle). Ex. Within the M phase – metaphase does
not automatically lead to anaphase. Proteins of the
cell cycle control system must trigger the separation
of sister chromatids.
-There are checkpoints in the cell cycle. There are
three major check points during G1, G2 and M phase. Signals within the cell,
detected by the control system, tell whether key cellular processes have been completed
before the cycle moves on. The system also receives messages from outside the cell –
indicating both general environmental conditions and the presence of specific signal
molecules from other cells.
G1 – receives the go-ahead signal from a growth factor and enters S phase. If this
happens the cell will usually complete its cycle and divide. If it does not receive the
signal to go-ahead it enters G0 (nondividing state). Nerve cells and muscle cells are in
G0 phase.
CANCER
Cancer cells do not respond normally to the cell cycle control system – they divide
excessively and can invade other tissues of the body.
Cancer begins:
-single cell goes under a transformation (process in which a normal cell converts
to a cancer cell)
-Body’s immune system normally recognizes a transformed cell and destroys it.
-If the cell escapes destruction it may grow to a tumor (abnormally growing mass
of body cells)
-If the cells (tumor) remains at the original site – the tumor is called benign. They
can cause problems if they grow in and disrupt certain organs.
-A malignant tumor can spread into neighboring tissues and other parts of the
body. Cancer cells may separate from the original tumor or secrete signal
molecules that cause blood vessels to grow toward the tumor. A few tumor cells
may enter the blood and lymph vessels and move to other parts of the body where
they from new tumors. Metastasis is when the cancer cells spread through the
circulatory system beyond the original site.
**Cancers are named according to organ or tissue in which they originate.**
**Four categories of Cancer
1. Carcinomas – cancer that originates in the external or internal coverings of the
body (skin or lining of the intestines)
2. Sarcomas – cancers in the tissues that support the body (bone and muscle)
3 + 4. Leukemias and Lymphomas – cancer of the blood-forming tissues (bone
marrow, spleen, and lymph nodes)
Cancers do not have the normal signals that regulate the cell cycle. They continue to
divide even at high densities. Many cancer cells have defective cell cycle control
systems that proceed past checkpoints even in the absence of growth factors. Other
cancers themselves make growth factors that make them divide continuously. If a cancer
cell does stop dividing it is random and not at the checkpoints. Cancer cells seem to be
“immortal” – they keep dividing.