A quick review, we certainly covered this in the
cell and molecular biology course. We have oncogenes
and proto-oncogenes. Oncogenes are those that can
potentially become cancerous or they will cause
a cell to become cancerous. Then we have
proto-oncogenes. Those are the genes before
they’ve become oncogenes. A proto-oncogene
is an early oncogene that has not yet caused a mutation
that results in cancer. So, there are
many genes involved in growth factor receptors
as well as proteins in signal transduction pathways,
the G-protein-coupled receptors,
so on and so forth. Then the thing is with the
sequencing of the genome, not only are we looking at
what these expressed phenotype genes do but we
also are now able to get a much closer look
on what each of the regulatory pieces of the genome
do also. So, as with other fields of genetics,
the more we learn, the more there is to discover
in essence as we go deeper and deeper
into our understanding of the various pieces of
the genome. Tumor suppressor genes,
some that we have covered that are important for
you to know for your exams are involved in
preventing proliferation of mutated cells in their
regular roles. That’s the whole meaning
of tumor suppressor. In their functional form,
they suppress development of a tumor by programming
a cell for apoptosis, let’s say. So, p53 was one
of those and the Rb protein as well as BRCA1 and BRCA2.
Remember that Rb was the first one that we
discovered. BRCA1 and BRCA2 are also tumor suppressor
genes that are involved in breast cancer.
They’re two that we have characterized fairly well,
not to say that they are the only ones.
But someone with BRCA 1 or BRCA2 mutations
are much more highly likely to develop breast cancer;
again, one of the classic multifactorial disorders
that we have considered previously.
There are also caretaker genes. Caretaker genes are involved
in repair of DNA. Let’s say the caretaker
genes are there and they’re supposed to be proteins
or enzymes that run along on the DNA and make
sure that it is all in order. So, one of the polymerases
to make sure that all the base pairs are in order.
They run into an error, they generally will stop
and correct that or prevent cell division.
These caretaker genes, if they’re wrong, they just let
the mistakes flow on by and the cell continues
to divide with this bad copy of the DNA in it.
When DNA repair enzymes are mutated, we also
have issues in cell cycle controls. That’s all
that it comes down to. Gatekeeper genes are again
another class of genes under the tumor
suppressor genes that will act to prevent growth
of cancer cells. Let’s say a cancer cell arises
with a new mutation, there are so many checks and
balances in place. Caretaker genes would say,
“Hmn, this one doesn’t look right. We’re not going
to let it divide.” Again, those precancer cells
would undergo apoptosis and not result in the
generation of cancer. If the gatekeeper genes are broken
then cancer could very easily develop. Those
cells could divide out of control. Oncogenes and tumor
suppressor genes are genes that you should
certainly be familiar with as a class of genes.
The three that I mentioned there are important
ones for you to understand their roles of.
If you need to go back and review how each of
those types of genes function, I recommend
that you take a look again in the cell cycle
controls portion of the cell and molecular biology course
because all the details are there.