BIOB11H3 Lecture Notes - Lecture 19: Stomach Cancer, Nuclear Power Plant, Aneuploidy

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Published on 21 Apr 2013
Biological Sciences
Lecture 19 cancer the biology of cancer
In the first couple of weeks, we talked about DNA replication and how it is regulated. We
also talked about DNA repair and the genes controlling DNA repair. We had 3 lectures on
the cell cycle. For the next 2 lectures, we will talk about is what happens when the cell cycle
gets out of control? This has to do with cancer. We will talk about how the cancer differs
from other cells, or the cancer phenotypes. We will learn about the types of things that
contribute to cancer, such as the environment and how molecular biology can be employed
to guide future cancer treatments. When you were 2 years old, you were learning language.
You had no idea you were going to die. When you became 4-5, you began to be more aware
of mortality and that people die. Eventually, you learn about cancer and you know someone
who has cancer or has died from cancer. What you will see today is that a large percentage
of the population has this in their future but eventually, you can take charge of your health
and your destiny by doing a few simple things. Figure 16-2 shows cancer statistics of the
USA. There are not a lot of difference between these statistics and what is going on in
Canada. Along the bottom are different types of cancers. Along the y axis is the cancer cases
per 100,000 people. Some are fairly high and some are fairly low. On the right side is the
number of deaths per 100,000 people. What is the highest on the list? If you live long
enough, males will get prostrate cancer but usually they don’t die from prostrate cancer
because there are test for early detection and blood test and prostrate cancer comes late in
life. Men and women can both die from breast cancer but the incidence of death is low
because it is fairly treatable. Lung and colon cancer have a very high death rate. Why? For
lung cancer, usually you need to remove the cancer but you need your lungs to breathe.
This is one part of the answer. If you thing about where these tissues come from and what
they do, you know that they are both epithelial tissue which means that they cover the
interior of the lungs and the interior of the colon so they are exposed to your environment.
Depending on what you breathe, if you smoke, etc these all affect your chances of getting
lung cancer. For colon cancer, you are what you eat. If you eat a lot of saturated fats, those
fats are metabolized to create intermediates. There are many chemical reactions that go on
every day and these reactions can result in mutation which can result in cancer. Obviously
you can have surgery to remove part of your colon or your stomach but of course you
needn't that tissue to absorb food and conduct life. These things are treatable but they tend
to be pretty severe cases.
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Differences between normal cells and cancerous cells. We will look at seven different things
and in each case we will have what the normal cell looks like and what the cancerous cell
exhibits. The first of the characteristics is suggested to be density dependent growth in the
case of the normal cell and the density independent growth in the case of the cancer cell.
This means that let's consider a class of cells which are normal cells and another of cancer
cells which are cultured cells. When the normal cells begin to multiply, and there are a lot
of cells in the environment, they began to slow down their cell cycle and sometimes even
stop the cell cycle. In cancer cells, they don't seem care about that, they just keep cycling
and cycling and not pay attention to the density of cells in the area. In association with this
phenomenon, there is something called contact inhibition that normal cells exhibit. That is,
if they divide and come in contact with some neighboring cells, they develop
communication between the cells that tells them when it's beginning to get crowded and to
slow things down. Cancer cells do not care for this and they continue to grow and divide
uncontrollably. Normal cells in culture and in the body as part of the tissue, have something
called anchorage dependent growth. They need to be touching other things in the
extracellular matrix, another cell or something in order to give them the signal to grow and
only when they do so do they carry out the cell cycle properly. In contrast, cancer cells
display anchorage independent growth. This means that as the cancer cells divide, it can
break away from the other neighbor that it was touching before and it can go to other
places in the body in order to set up other secondary tumors.
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Figure 16 3 shows a culture of normal cells at the top. What you can see is a culture of
normal cells at the top. When the cells contact their neighbors and the dish becomes very
dense, the cell cycle arrests. They just sit there in a monolayer which can be seen from the
side view. If you look at this growth property with cancer cells what you see is that they
exhibit density independent growth and also contact inhibition. The cells pile up on top of
one another to form tumor-like masses. This is the same thing that would happen if there
was a mutation in the cancer cell developing in the colon or lungs and they would continue
to divide and grow uncontrollably to make a tumor.
The fourth one is that normal cells require growth factors in order for them to do their
normal cell cycle controls. Cancer cells do not, In fact they often produce their own growth
factors to further simulate their division. This is shown in figure 16 4. Along the bottom is
time in culture in days and along the Y axis is the cell number. Normal cells in culture that
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