November 8, 20135:40 PM
Can see that the major impact cancer has on individuals. Also on
We all are impacted by cancer.
We are going to see the theme that The molecules that are defected
with cancer are the molecules that we talked in past lecture.
We are talking about defects in the molecular machinery that concerns
the see slide.
Important to understand the cell biology principles to combat cancer
and other diseases
BIO230 Page 1 This diagram highlights the molecular machinery pathways in cancer.
When you look across, there are many molecules that we discussed.
Cadherin's, integrin's, control of cell growth, control of cell death and
many of these aspects we discussed.
When humans develop they start from one cell and end up with
hundred thousand billion cells. Of those billion cells in our body there
are many cells experiencing a mutation every day. So there are insults ,
changes in our DNA everyday.
Normally these mutations, most of them will be repaired. By the DNA
repair machinery which is constantly scanning the genome and
10 Cells in human body
checking for errors.
If there is a problem with repairing that DNA the then the body cant
repair the aberrant cells. Then the --> p53 is activated and the cells are
killed. There are two layers of protection, correction at the molecular
level and destruction of the cell that protects us from mutations.
The problem arises is if that one of these cells, if it gains a mutation
that allows it to survive and divide it will grow a tumor. If there is one
dangerous mutation that doesn’t allow for apoptosis ,This is a
Cancer origins from one single cell. Clonal in origin from one cell.
BIO230 Page 2 One example that gives evidence for the origin of cancer is shown here.
The basic idea is that we can distinguish 2 cell types in this tissue
sample. That’s because These cells are from the females and they have
2 X chromosomes and one of these X chromosomes is inactivated for
dosage compensation. Males have an X and Y, and so one X is
inactivated in females.
There is one X and less active Y in males.
This inactivation is random so when you look across the tissue one X
chromosome is inactivated in the pink cell and one X is inactivated in
the grey cells. You can see the random organization here. So all of these
tissue around the outside if the diagram will be normal tissue with
random inactivation and in the center this is a tumor.
In the center, there is a tumor. The tumor cells are indicated in pink
because a probe for one X chromosomes shows that all of these cells
have the same X chromosomes inactivated. This is one piece of data
that indicates that cancer is a group of cells derived from a single cell
because they all have one X inactivation.
If it was derived from a group of cells, then there would be one mixture
of chromosome inactivation in another one like the surrounding tissue
This provides that the evidence that the mutation occurred on one cell
and it started and divided forming the tumor there
dangerous thing about cancer is that they have uncontrollable growth.
So you can monitor the tumor cell doublings and then monitor the
diameter of the tumor and notice the exponential growth
You start off from a single cell an after 30 doublings you can see the
tumor on the x ray. And after 35-34 the tumor is palatable that means
touchable and can be surgically removed at that point. And then after
40 doublings then the tumor becomes deadly. If you look at the size its
100 mm across. The you have a 10cm wide diameter. It's like a baseball
and this is what kills, you have abnormal cell growing within a normal
organ and now you end up with 10cm in diameter inactive group of
cells which disrupts the rest of the organ function.
That’s detrimental to the overall body. This is what ends up killing
BIO230 Page 3 Can we categorize cancer cells by tissue type?
Definition if a tumor is an uncontrolled growing mass of abnormal cells.
Epithelia are the tissues that coat our skin and organs. They are called
carcinoma and the cells in-between the epithelia are found in the
Uncontrolled growing of mass of abnormal cells connective tissue. Can be either Muscle cells, neuro cells, blood cells.
Etc. They can be broken into two types.
These are sarcomas.
Blood cell cancers are leukemia.
This relates to the single cell that started to divide. We can also
describe different stages of cancer development.
There are stages as the cancer become more dangerous.
This is a begin tumor:
Epithelial derived tumor. Around the outside we have the Ecm of the
basal side of the tissue and have a growing mass of abnormal cells. This
is not crossed the ECM to pass into a nother body complartments. We
call this as being tumor, growing mass that is self-contained as a single
tumor. Haven't left the ECM. Not as dangerous. As long as they are not
causing disruptive to functions.
Malignant tumors are dangerous:
The cancer cells are dividing which derived from one of the normal cells
that gained the mutation to form the group of cells. The cancer cells
start dividing forming a group of cells and In malignant cases some
break from the ECM barrier and start to go to the surrounding tissues.
This is an aggressive tumor that is broken free and invade the
surrounding tissue. This is relatively local. This will go to the
surrounding connecting tissue and the cancer cells are moving into the
connective tissue underneat the epithlum in this case.
Now the next level of concern is when the tumor becomes metastasis.
This is when the cancer starts to inavde other tissues and then form
metastasis secondary tumors.
BIO230 Page 4 This is when the tumor becomes epistasis. Starts to invade the other
tissues through blood cell.
Step 1: start will normal epithelium. Basal lamina specialized Ecm below
the epithelium cells.
STEP 2: one cell starts to grow uncontrollably after gaining a mutation
becomes e benign tumor.
Step3: it break through the ECM. The cells gain more individual
properties and become migratory. Migrate away from initial site. They
act like WBS crawling through the ECM.
Crawl through the connective tissue , ecm, binds to blood vessels and
pass through the epithelium that is coating that blood vesseil and pass
into the blood.
This environment in the blood is not hospitable for the blood cells. So
most of them will die. One in a 1000 will survive. Those that did survive
will pass through the blood stream and can find a region where the
blood vessels become narrow and now these cells can leave the blood
vessels and then they can populate a tissue outside the vessel at a
second site in the body and this single cell and start growing again and
start a second tumor. So we have the primary tumor which is present
and then secondary tumor somewhere else. All of these sites are
growing and disrupt multiple organ systems ebcause of the grewoing
size of all the tumors. These are cellular changes of cancer
Now let's consider the molecular changes in cancer cells
The first change in a cancer cell is changes in DNA.
There is a single cell that has changes in DNA,
In this example there is a dramatic change in the DNA
This is a karyotype where the chromosomes of a cell samples is spread
out on a cover slip and we can analyze their organization. We can
analyze their chromosomes.
These are labelled with specific dyes that can distinguish one
chromosmes from the other. So we can distinguish a set of
chromosomes from dyes and we can color code the results from dyes.
What goes wrong in the cancer tissue, now we have T in this cancerous
tissue, single cells where we have 4 copies of chromseoms one,
multiple copies of chromeoms 2 and some look like they are
fragmented. Look at the othere example. In addtion to having a copy
the chromeosme , some ieces of chromsoems have transcloated to
other chromeosmes as well. Green and purple conencted. This tissue is
in a cancerous cell that has progressed faraway. Because in the intital
event may only be a comuple of mutations. These cancer cells start to
lose control of themselves. Gain more mutations and they don’t follow
the checkpoints and so progeny of the cencer celldivisions end up with
extra chromomes. And these problems will build and build and cancer
cells will ebcome more and more abnormal and dangerous.
Cancr cell that has progressed far away.
BIO230 Page 5 The intial change in the cell is a Change in DNA. What causes the
mutations leading to cancer. What genes are mutated and how did they
prmote cancer progression?
When you think about what is causing cancer mutations is chemical
Mutations can also be cause d by radiations, and viruses. They can
change the DNA in the cell and if its changedin a wrong way it can cause
Chemical mutagen: how does it lead to the change in DNA.
This structure looks This chemical is called afflotoxin: this is found in mouldy peanuts.
If you ingest this afflotoxin in our body can be acted upon by this
similar to a nucleotide. enzyme which convert it into this derivative called afflotoxin epoxide
and afflotoxin epoxide can bind to gunaine in the DNA. There is a
gunaine and there is an abnormal molecule attached to the G. When
you look at the moelcule what does it look like? It looks like, compared
to guanine, similar to a nucleotide. What's going to happen is as you
know G will base pair with C but because G is bound to this molecule it
will no longer bind to C. so a C now will not be added by base paring to
the newly synthesized DNA strand and therefore will have an deletion
of the C.
This is an example of how to have a moelcule that looks like a DNA base
The key thing here is it is not the intiial moelcule that is the problem
but the body enzymes in the body modifes it into a form that covalently
Exmaple on how to get a molecule that changes DNA leading to the deletion of C.
looks like a DNA base pair
BIO230 Page 6 How to figure out which molecules are safe and what are not. All sorts
of government labs, when new products comes to the market that are
going to be exposed to humans, agencies are going to run the
compound through this test.
The products are run through this tests and found if it can mutate DNA.
All that is asked is if it can mutate DNA. If it can mutate DNA then you
don’t want to ingest it because DNA mutations leads to cancer. The
assay here is to ask if the chemicals are leading to mutations in DNA
makes use of bacteria. The actual DNA we are assesing is bacterial DNA.
Reverted the mutation The actual DNA they are accessing is bacterial DNA, and this bacteria is
Back to normal. That’s why you special in this test. We are checking salmonella, but this salmonella has
The ames test. See the one path a mutation in its enzyme for producing histidine. On its own the
bacteria if you plate it on media that doesn't have histidine on it, takes
the bacteria --> put on media, it will not grow. Because there are no
However, you see that one colony of bacteria that has grown, and the
only way it could have grown is because if there was a mutation in the
salmonella that if you reverted the broken enzyme back to normal.
Normally you think about mutations disrupting gene function. Now we
look and ask if these mutations can repair the broken enzyme. Now this
particular salmonella cell will now be able to grow without histidine and
make a colony. You may ask isnt that going to be extremely rare? Then
these mutations can be happening all across the bacterial
chromosomes. What are the chances that there mutations is affecting
the histidine producing gene specifically?
The chances are extremely low. Its like winning the lottery. This is why
we use bacteria because in one culture you can have millions and
millions of bacterial cells.
So you can actually pick that 1/ million event because you have millions of bacteria. That’s why bacteria is critical in this test. If you take the test compound that you are worried about, plate
them out it with salmonella, plate it and ask when you add the chemical does it lead to the greater bacterial growth of the cell colony. So that means more mutations occurred and brought the
histidine mutation back to normal. Compared to background will there be a more reversin or more mutagenesis vs background. You can see that this is a compund problem.
Why are we adding the homogenized live exrtact? We have a purified compounds, and pure sample of histinde dependnt salmoenlla now why are we adding this extract? Lets look at this with a
Why is the liver extract added: 1. supplies the cells that are cancerous. Incorrect because there are no cancer cells in theassay at all. Its bacterial cells we are looking at. 2. supplies the cells that
might be modified to become cancerous. Incorrect we are using bacteria cells. 3. provides chemicals that might cause mutations. - incorrect. It came from purified chemicals. 4 modifies
chemicals the purification came from. This is the key thing. We saw with afflotixin , if you took that afflotixin and put itinto this assya there wont be any problem. Only after the afflotixi is
modified by enzymes in the huamn body are they modified into the cancerous form. So by adding the liver extract we not only testing the chemicals, but also any forms of the purified cacner
cells the body might make.
BIO230 Page 7 There are 2 classes. Oncogene and tumor suppressor (TSG).
Oncogenes : gain of function genes
Normal forms are called proto-oncogenes.
Ras and Myc are proteins that drives the cell cycle forward and premits
cell proliferation. So tehre is a gain o ffucntion within these genes
which causes more cell proliferation.
This is a problem with cancer.
Gain of function
Cancer is arising from loss of function. P53 and Rb holds the cell
cycle back. If we remove these players there is a greater chance of
cell proliferation and they will die.
Loss of function
One thing that arises is that the tumor supressor genes are recessive.
Oncogene is domainnt.
W start with two copies of our chromosome, and with the overactivity
mutations gain of function for the oncogene, all we need is just one
copy to turn on and we don’t need the other copies to function. We
need to increase the total level of cell cycle promoting signal.