Hi. It's Mr. Andersen and welcome to biology essentials video 32. This is on
signal transmission and gene expression. It sounds confusing but it's actually fairly
simple. One of my favorite videos I've ever seen on YouTube is the guys who jump off the
mountains in Norway with these wing suits on. And they'll fly right over the earth,
just kind of skimming it. Even though they're falling it's like they're flying. Now I would
imagine as they're doing that adrenaline just must be coursing through their body. They
must have heightened heart rate. They must just be really alert. And so that actually
has a lot to do with biology. Adrenaline is made up of epinephrine. And epinephrine is
a chemical that will move through your body and gives you all these physiological effects.
If you've ever been almost in a car accident and you feel this heightened alertness and
your heart rate is racing. You start to sweat. All of that is this fight or flight
response. And that epinephrine, just a simple chemical, as it moves through your body, can
have all of these huge consequences. And so that's what this podcast is, it's not about
wing suits but it is about that. And so signal transmission is chemicals that move throughout
your body. There are couple of different ways that we can transmit those signals. They can
move intercellular. That mean from cell to cell to cell. And they can also move within
the cell itself. And so I'll show you some examples of that. Know that chemicals aren't
limited to the cell. They can move throughout your body. And the endocrine system is an
example of that. The specific example I'll talk today about is epinephrine. Epinephrine
remember is that adrenaline. And what it can do is it can change cell function. It can
change what a cell is doing or what a cell is producing. Example I'll talk about is how
it can create and activate phosphorylase, which can actually free up glucose. Glucose
remember is that energy coinage in our body. We use it to make ATP. And so epinephrine
can cause cells, especially in your liver to give off glucose. They can also actually
cause gene expression. They can actually cause the DNA to express different proteins. An
example I'll talk about is the CREB transcription factor and how that can also increase the
amount of glucose that's given off. And also add to that fight or flight. And so what are
we talking about? Well the liver, which is this right here, the liver actually is one
of the larger organs in the body. But it contains glucose. It contains glucose in the form of
glycogen. So it's a bunch of glucose molecules attached together. And so what epinephrine
can do is it can actually go into glycogen. It can spread throughout all the cells of
the liver and cause them to give off glucose. But in this pod cast I'm going to show you
how that actually occurs. In other words, how we can have epinephrine out here. It can
move from cell to cell and cause the production of glucose. And how it can also go all the
way into the nucleus and cause changes in gene expression. And so this seems confusing.
And I have left off all the names of all of these things to make it a little simpler.
But what I'm going to show you today is something called a signal transduction pathway. And
I think it will make sense when I'm done. And so what do we start with? Well first of
all this is going to be the inside of the cell. And this is going to be the outside
of the cell. And so where's the message come from? It comes from the adrenal gland in the
form of epinephrine. So epinephrine is a chemical. It's just going to diffuse throughout your
whole body. And let me show you some other parts. This is called a receptor protein.
It picks up that message from epinephrine. And these are all different types of proteins.
And so this is a G protein. This protein will, I'll show you in just a second. And so what
happens with epinephrine? Epinephrine will actually latch on to the receptor and it causes
a change in the shape of that receptor. That will actually phosphorylate or add energy
to this other protein. That other protein will attach on to this red protein and now
it acts as an enzyme. And it's an enzyme that makes cyclic adenosine monophosphate. And
that seems like a scary word, but you know what this is already. ATP is adenosine triphosphate.
And if we loose two of those phosphates we now become adenosine monophosphate. And you
actually get this circle bond forming where that phosphate is. And that's where the cAMP
or some people call it camp comes from. It's just converted from ATP and it uses this activated
enzyme to do that. Okay, what happens to that camp or that cAMP? It'll actually go to another
protein. And that protein has four different parts to it. It has these parts, which are
catalytic. They're activated. And these are regulatory. And until the cAMP shows up, then
we don't release those catalytic enzymes. This whole thing is called a protein kinase.
So now with cAMP available, now we have this active catalytic subunit which can activate
phosphorylase. It's actually going to transfer a phosphate group to it. And now we have phosphorylase
which can actually break that glycogen into glucose. And we can free up that glucose as
a part of that fight or flight response. Now you might be thinking, this is like some kind
of a mouse trap game where you have one thing come in or Rube Goldberg device where you
have all these steps to eventually just release glucose. I mean why doesn't epinephrine just
flow right into the cell? Well number one it can't move across this lipid layer. But
the other thing that I'm really not showing you is that there's not only one G subunit
that moves, this branches out to a bunch of these. And this breaks out to the cAMP. And
each of these can activate a bunch of these protein kinases. And this can activate a bunch
of the phosphoryl. And so at each step along this signal transduction pathway we can amplify
that signal. And so we can have just one epinephrine create billions of glucose molecules. And
so not only do we have control at every step, but we can also amplify that. And that's the
importance of signal transduction pathway. Just a few signals can lead to a bunch of
glucose. Okay. So that would be change in the cell function. We went from a cell that
doesn't release any glucose to one that releases a bunch of glucose. But I also said that we
can actually use it to do gene expression. Or express different genes. And so if you
look here, this looks exactly like it did before. But let's say that I were to remove
one thing. Let's say I were to remove that protein that actually breaks down the glycogen.
Are we out of luck? No. Because epinephrine can do the following. And so in order to make
that protein, remember, we need DNA to express a protein. And so the only thing I'm doing
is I'm removing the protein. I'm adding the DNA and adding one more chemical called CREB.
CREB is simply a transcription factor. And so what happens next? Well epinephrine is
going to show up again. It's going to attach to the receptor. It's going to phosphorylate
that protein. It's going to make our cyclic AMP or our cAMP. That's going to activate
our protein kinase. It's going to release those catalytic subunits. But now instead
of these activating the protein, watch what happens to the catalytic subunit now. It actually
activates CREB. CREB is a transcription factor. So it adds to the DNA. There's a few steps
that I'm not showing you here, but what it really does is allow RNA polymerase to grab
on. Make messenger RNA. Make a new protein. This is called phosphatase which is part of
this breakdown of glycogen as well. It's activated by that catalytic subunit. And now we can
make more glucose again. So even though we didn't have the protein, we can now make a
bunch of that glucose really really quickly. What's the only thing we've added? We've now
added this transcription factor CREB so we can actually make more of those proteins.
And so the whole point of signal transmission and signal transduction is that we can receive
a signal. That signal can activate a series of events which will eventually have an action.
In this case we're expressing the genes. Now some of these signals, instead of actually
hitting a receptor on the outside can actually move through and move into the nucleus and
act that way as well. And so that's how you get that fight or flight or just one part
of that response. And so that's gene expression. That's signal transduction. And I hope that's
helpful.