So receptor tyrosine kinase pathways and G-protein
coupled receptor pathways are two different approaches
to second messenger systems. Basically, all of our
second messenger systems can be grouped in either
receptor tyrosine kinase or G-protein coupled receptors.
So we are going to take a look at how each of these
work and then explore each in a little bit more depth.
So receptor tyrosine kinase pathways are generally
involved in regulating normal cell processes. So
when things go wrong with receptor tyrosine kinase
pathways, we see that cancers can evolve or we could
see neurological disorders because cells have lost
their natural functioning. In fact, receptor tyrosine
kinases are very active area of research currently.
There are over 90 receptor tyrosine kinase genes that
have been identified as of this point in 2015,
and there are many more coming almost every day. So,
the general principle is that the signal molecules
will bind to two receptor tyrosine kinase modules
and they will come together and diamerize,
and they will be activated by phosphorylation just
like many other systems. And that will activate
a protein that will then activate a whole cellular
response. We're going to look at it in much more detail.
The other system that we have are G-protein coupled
receptors. We've already taken a brief look at those.
G-protein coupled receptor pathways are generally
involved in mediating structural and metabolic changes.
So, receptor tyrosine kinase is generally for normal
processing of cells. Their normal daily activities.
But if we wanted to make a change move, change the
production, something like that we would be using
G-protein coupled receptors. So first of all, what
we see is a first messenger will bind to the receptor.
And the receptor will then create a G-protein reaction.
So the G-protein then goes to activate some other
effector. An enzyme that's in the membrane. We'll look
at a couple of different specific examples shortly.
Then we have our inactive second messenger. Gets
phosphates or drops off phosphates at our enzyme
and becomes active. And that second messenger, these
are our fire guys. Running out to take care of the fire.
They'll amplify the signal activating some more kinase
proteins and then activating a full cellular response.
So, very similar things happening as a result of
both receptor tyrosine kinase pathways and
G-protein coupled receptor pathways. Just a
slightly different mechanism of how they happen.
So both of these second messenger systems
can facilitate signal amplification.
What we mean by signal amplification is simply that
the first messenger will tell the second messenger.
And the second messenger tells many other messengers.
And they pass the message on to many others.
And so with each step in the signal transduction
pathway, the signal is amplified.
So in that way one molecule reacting with one
receptor can have a very large cellular response.