Hi. It's Mr. Andersen and in
this video I'm going to talk about epigenetics. In science there's this age old question,
are you the way you are because of nature or nurture? In other words, am I the way I
am because of the genes I inherited from my parents or from the experiences I have during
my life. And a great place to study this is using identical twins. And so if I had an
identical twin, we would have exactly the same DNA. But we wouldn't look exactly the
same. And that's because during our life we're going to have different experiences. Get different
nutrients at different times and so we would be different. And so nurture is important
but so is nature. But what we're finding is that the delineation between nature and nurture
is blurred. And a great study that relates to that and epigenetics came out in 2003 when
they were looking at mice. And so this is going to be a typical mouse. It's grey in
color. And it's going to be relatively thin. It's a normal mouse. But there's a mutation
found in mice called the agouti mutation. You have the agouti mutation, you're not going
to be dark in color. You're going to be this kind of yellowish color and you're going to
be fat. You're going to be obese. And associated with that, you're going to have a higher incidence
of diabetes. You're going to live a less amount of time. And what they found is that the scientists
could actually take cloned mice, mice that were exactly the same and by feeding the mother
different amounts of nutrients, they could produce agouti mice. In other words they could
produce mice that are genetically identical. So they have the same exact DNA. But they're
going to express different genes. And so that's what epigenetics is. It's taking the genes
that we have and manipulating those. And we've known about this for a long time. And so if
we look at some stem cells. These are stem cells here. Those are going to become the
cells that are eventually an adult. They're going to have all the same DNA in all the
stem cells. But we know that as those cells eventually start to become different cells
and different cells and different cells, they're going to differentiate. They're going to turn
into different cells. And so the DNA is going to be the same between all of those cells.
But the genes that they express are going to be different. And so what they have is
they have all the messages to make all the different types of cells inside the DNA but
they're not expressing all of those. And so what is epigenetics? Epigenetics is controlling
which genes we're going to express at which time. And so if we express just the lip genes,
then we're going to make a lip cell. And if we express just the eye genes, we're going
to make an eye cell. And if we express the ear genes were going to make an ear. But if
we express all of them at the same time we're going to make a cell that clearly doesn't
function. And so this is something interesting that you should know. That all of our cells
have the same exact DNA. But they're not expressing all of the genes at the same time. We call
that differentiation. How do we control what genes are actually being expressed? It is
called epigenetics. And so we finally come up with a definition for it. And if I were
to read it out its "Stably heritable phenotype resulting from changes in a chromosome without
alterations to the DNA sequence." What does that mean? Well remember phenotype is going
to be the physical appearances that you have. And so what epigenetics does is allow us to
change the phenotypes without changing the underlying DNA sequence. And this is heritable.
In other words once we change that you can actually pass that on to the next generation.
And so before we talk about the specifics of how epigenetics works, we should really
talk about what DNA is. So DNA remember is going to be a code and it's code to make all
the proteins inside the cell. It's found in all life. But DNA just doesn't sit loose within
the nucleus. It's made up of something called chromatin. And chromatin is basically two
things. You have the DNA, which is going to be the genetic code. And then you're going
to have these proteins. They're called histone proteins. And the DNA is wrapped around the
histone proteins. The histone proteins are wrapped around themselves. You eventually
get threads and fibers. And you eventually get what we think of as a chromosome. And
so what is a chromosome? It's a bunch of proteins with DNA kind of wrapped around it. And so
in epigenetics what we want to be able to do is to express specific genes. And so how
do we do that? There's basically three mechanisms of epigenetics. And the first one is called
DNA methylation. So what does methylation mean? It means we're adding a methyl group.
We're adding a functional group. In this case we're adding it to cytosine. So remember DNA
is going to be made up of four different nucleotides. We have adenine, cytosine, guanine and thymine.
And the one I'm talking about right here is called cytosine. So this is going to be a
nitrogenous base. It's going to be those rungs on the inside of a ladder. And if we methylate
cytosine what that really means is we're adding a methyl group. You can seen the methyl group
right here. We're adding a methyl group to the cytosine nucleotide which is going to
be found on the inside of the DNA. When we do this, when we methylate cytosine, it's
almost like turning a switch off. So we're turning that gene off. And so basically RNA
polymerase now can't grab on to the DNA. It can't make RNA and it can't make those proteins.
And so once we methylate our DNA, we are turning it off for good. Now where is it a good example
of this? Well this is going to be a fertilized egg or a zygote. That eventually makes stem
cells. And those stem cells eventually are going to differentiate to make all of the
cells in our body. But how does it do that? Well again it does that by methylating the
genes. And so inside the circulatory system, let's say a heart cell, we're going to methylate
all the genes that don't make that heart cell. And so the same thing is going to happen in
all of the cells in our body. Now an interesting thing, well how do we make those stem cells
in our children again? Well when we're forming those cells, those gametes cells, we're going
to demethylate the DNA. So we're going to remove the methyl groups and now it can become
a stem cell again. So that's one mechanism. Histone acetylation is going to be another
one. So remember we said the DNA is wrapped around these histone proteins. And so how
tightly is that DNA is wrapped is going to determine if we can express the genes on the
DNA or not. And so if the DNA is wrapped really tightly then RNA polymerase can't get on.
We can't transcribe those genes. And so that's controlled by a couple of different enzymes.
And so before we get to the enzymes, we should talk about what a histone is. A histone is
going to be a protein. So it's made up of a number of different amino acids, but the
important ones are going to be lysine. So lysine is going to be a specific amino acid.
You could see here's the R group hanging off the end. And what we could do is we can add
an acetyl group to that. As we add an acetyl group to that, right down here, what that's
really going to do is it's going to change the structure of these histone proteins. And
that's going to loosen up the DNA that's attached to it. Once we loosen up that DNA then we
can start to transcribe the genes that are found wrapped around the histone. It's almost
like having thread wrapped around a spool. And if we loosen up that thread, then we can
start to code for those genes. What if we don't want to express those genes? Well we're
going to go in the other direction. We're going to remove that acetyl group. And so
the functions, or excuse me, the enzymes are going to be histone, acetyl transferase. And
that enzyme is going to transfer an acetyl group on to the histones. And then we're going
to have histone deacetylase. And so that's going to remove the histone group. And so
again, what does that mean? If we add the acetyl group to it, then we can code for the
genes here. If remove the acetyl group, then RNA polymerase can't get on to the DNA and
we're not going to code for it. And so this is occurring all of the time. It's not like
methyl groups when we're just turning a gene off permanently. We're constantly acetylating
and deacetylating those histones. And so we're coding for the genes. And then we're not.
And then one other important thing that we're starting to discover is something called microRNA.
MicroRNA is little bits of RNA. And so let's kind of figure out where we are. This is the
nucleus. So this would be a eukaryotic cell. This is going to be the RNA. And then this
is going to be a ribosome. Ribosome remember is going to translate that protein. And so
what we also produce inside our DNA is we're producing a bunch of microRNA. MicroRNA is
little bits of RNA that aren't going to code for specific proteins. What they're going
to do is they're going to bond to the regular messenger RNA. When they do that they block
the ribosome. And so we can't code for those specific enzymes. Can't code for those specific
proteins. So it's another way that we can say, okay we've got the DNA. We've got the
gene, but we're not going to make the protein because we're going to control that post-transcriptionally
after the RNA has been made. So why is this important? Well it's super important that
you take care of your genome. Because that's what you hand on to your kids. But what we're
finding is it's your epigenome thats incredibly important. And so we can mess up our genome
using all of these things over here. Changes in diet, drugs, getting older. All those things
are going to change what genes we're actually expressing. And the neat thing about that
and the scary thing about that is that we pass that on to the next generation. And so
diabetes, we found forever that diabetes is going to be much more common if you have a
parent who has diabetes. Well, what's going on? They're actually changing their epigenome.
They're changing what genes they're expressing and then they're handing that off to their
kids. It's a little bit scary, but that's epigenetics. It's really cool. It's revolutionizing
a lot of the ways we look at health problems. And I hope that was helpful.
