Download Cancer and the Cell Cycle

Mitosis and Cancer
I. Multicellular organisms constantly need to make more cells!
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Each minute your body needs to make ...oh...about 300 MILLION NEW CELLS!
A cell spends a good part of its life in a "G-phase" (growth phase) working
and growing, breaking down sugars, synthesizing proteins, enzymes, and other
macromolecules. However, cells inevitably wear out, break down and suffer
injuries.
In addition, as organisms grow and change, they need
new cells to make more skin tissue, bone tissue,
muscle tissue. These new cells can only come from one
place: OTHER CELLS - through the process of cell
division, or mitosis.
For multicellular organisms (like us) cell division
allows an organism to grow and develop from a
single cell to trillions of cells, to repair and replace
cells worn
out and used up by everyday life, and in some cases, to make specialized
cells for reproduction.
o Somatic Cells: (Mitosis) body cells of an organism that do all the 'daily'
functions of the organism as mentioned above.
o Germ Cells: (Meiosis) reproductive cells - eggs and sperm involved in
starting the next generation....
II. Cancer: renegade cells escaping the controls on cell division:
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What is Cancer?
o Cancer is the uncontrolled growth and division of cells. Cells will keep growing and
dividing, even if your body does not necessarily need them. This means that there is a
malfunction in the body in knowing when to start and stop mitosis. The cell usually spends
most of its time in interphase and spends a very small amount of time in actual cell dividing
phases. However, cancer cells are in a rapid state of cell division and spend much more
time out of interphase.
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How Are Cancer Cells Different than Regular Cells?
o Cancer cells behave differently than normal functioning cells. This also means that they
likely have different physical characteristics. Cancer cells often have these traits:
They spend less time in interphase – therefore they are dividing more!
They have uncontrolled mitosis – the means they do not stop division after a certain
point.
They grow faster than normal cells
They can break away from groups of cells and travel to other places in the body.
They have a different physical structure
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What Are Some Causes of Cancer?
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o There are many causes of cancer. All of these things increase the likelihood of cells
becoming mutated. Mutated cells may not be normal and develop an incorrect cycle of
mitosis. They will then keep reproducing at a high rate, causing the body to put lots of
energy into their production and upkeep. All of this energy being devoted to these cancer
cells causes other normal cells to suffer and can ultimately lead to death.
o Causes of Cancer (things likely to increase the chance of mutated cells)
Chemicals – many chemicals cause mutation, leading to problems with mitosis
Ultraviolet (UV) Radiation – When tanning or exposed to the sun, you absorb UV
light. UV light causes DNA to be mutated which can alter the cell mitosis cycle in the
future.
Viruses – an example is the HPV virus, which is known to cause cervical cancer in
females if they are exposed.
X-rays – they radiate cells, causing mutations
Genetics -- some people are born with genes that are more likely to mutate over
time or have cancerous properties. If cancer runs in the family, then you are likely
to have a higher risk of getting cancer.
1. Cancer is essentially a disease of mitosis - the normal 'checkpoints' regulating
mitosis are ignored or overridden by the cancer cell. Cancer begins when a single cell is
transformed, or converted from a normal cell to a cancer cell.
Often this is because of a change in function or a DNA mutation that occurs in one
of several genes that normally function to control growth. Examples:
(1) the p53 gene, the "guardian of the genome", usually functions to properly control
the cell cycle. However, p53 is mutated in over 50% of all human cancers.
(2) the BRCA 1 gene, the "Breast Cancer Gene" normally functions to supress tumor
formation; but if a gene contains mutations such that BRCA1 does not work properly,
tumor formation can begin (Note: mutations in this gene do not mean that a person
will develop breast cancer, just that they have an increased risk for breast cancer).
Once these crucial Cell Cycle genes start behaving abnormally, cancer cells start
to proliferate wildly by repeated, uncontrolled mitosis.
2. Tumors - Good Cells gone Bad...? The cancer cells proliferate to form mass of
cancer cells called a tumor. As the tumor grows larger, it begins to release proteins
from
the cell to attract new blood vessel growth (this is called angiogenesis). At this point the
tumor contains ~ 1 million cells and is about the size of a 'bb'.
Benign: tumor cells remain at original site. Can be removed surgically or killed by
radiation, usually eliminating any further cancer development at that site.
Malignant: some tumor cells send out signals that tell the body to produce a new blood
vessel at the tumor site. These cells not only have their own food and oxygen supply,
they also have an avenue for escape to a new part of the body - through the new blood
vessel and into bloodstream. Cells that break away from the tumor begin to spread to
surrounding tissues (via the bloodstream or lymph) and start new tumors = metastasis.
Usually surgery is performed to remove the tumor, followed by radiation and
chemotherapy.
3. Unusual features of Cancer Cells.
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(1) Cancer cells are frequently "immortal": whereas normal cells divide about 50 times
and then die, cancer cells can go on dividing indefinitely if supplied with nutrients (A
common laboratory cell line, HeLa cells, was originally isolated from a tumor in 1951 and
is still growing).
(2) Cancer cells ignore the usual densitydependent inhibition of growth in cell
culture (or in body tissues), multiplying after
contact with other cells are made, piling up
until all nutrients are exhausted. Densitydependent inhibition of growth is a control
mechanism when cells reach a certain density
they will stop reproducing. If some cells die
the density becomes less and the cells will
reproduce to regain the same density and
then normally stop.
(3) Cancer cells may also have an abnormal
cell surface; instead of "sticking" to its
neighboring cells, cancer cells tend to "round
up" and break attachments to its neighbors
cells, allowing for metastasis.
(4) Cancer cells often have unusual numbers
of chromosomes or mutations in
chromosomes. Aging, exposure to toxins
(like components of tobacco tar), mutagens
(like ultraviolet light) all cause mutations in
genes and cancer; but normal errors in DNA
replication can lead transformation of the cell
if they occur in a crucial gene.
Stopping cancer cell growth:
Chemo Drugs that stop DNA synthesis/ replication:
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Adriamycin and Cytoxan prevent DNA from unwinding properly,
5FU inhibits incorporation of T nucleotides
Methotrexate and 5-MP prevent cells from making nucleotides
ARA-C is a C nucleotide "mimic" that gets incorporated and stops further DNA
synthesis
No DNA replication, no new cancer cells!
Chemo drugs Taxol and Vincristine, both natural products from plants, work by
inhibiting spindle fiber formation and disrupting mitosis. No mitosis, no new cancer
cells
Common Chemotherapy Drugs
You probably know someone, maybe a friend or family member, who has been
diagnosed with cancer. If the cancer is found to be benign, usually the recommended
course of treatment is removal of the tumor, followed by radiation therapy to destroy
Cell Cycle Unit
any remaining cancer cells at the site of the original tumor. If pathologists determine that
the cancer cells are malignant (have traveled to the lymph nodes, or have cellular
characteristics that suggest malignancy), a recommended course of treatment
chemotherapy, sometimes called "chemo" - a slang term meaning "drug therapy with
chemicals".
Most chemo drugs are known as "anti-neoplastics". [anti-nee-oh-PLAS-tics.] neoplastics being cancer cells. Most antineoplastics work by stopping cell division in
one or another stage of the cell cycle. They cause cell death in any dividing cell, and
since most human cells are not dividing all the time, they preferentially kill cancer cells.
But any human cell types which divide frequently are also killed: cells in the
gastrointestional tract, the bone marrow, and hair follicles. These are reversible
processes and will symptoms will disappear when the drug is discontinued. (But the
cancer cells will be hopefully killed by then.
Cell Cycle Unit
Cancer Growth Animation Worksheet
Using the reading, answer the following questions:
What Is Cancer?
Cancer is when what cell process is uncontrolled?:
__________________________________
Normal cells of the body spend most of their time in which phase of mitosis?:
__________________________________
How Are Cancer Cells Different From Regular Cells?
List the 5 ways that cancer cells are different than normal cells of the body:
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List the different possible causes of cancer given in the reading:
o All of these items increase the likelihood of cells becoming
________________________, which means that cells may not repair and follow a proper
cell division cycle.
View the cancer growth animation either by clicking on the following url:
http://www.pbs.org/wgbh/nova/cancer/grow_flash.html
Answer the following questions from the animation
1. What type of cancer is studied in the animation and where does it form?
2. How many cells are in the human body?
3. Identify two things that can cause mutation?
4. Why do normal cells usually reproduce?
5. What is angiogenesis?
6. What is metastasis?
Cell Cycle Unit