Before we do that, we need to consider the concept
of phosphorylation. I've introduced already
the idea that ATP is the energy currency molecule.
So we phosphorylate or add phosphates to ATP
in order to make it high energy and then we can
release energy from this energy currency molecule
by removing a phosphate. Similarly we can phosphorylate
proteins. And this can either act as a deactivator
or activator of a signal transduction pathway. So it
can literally turn a process on or it can turn a process off.
Sometimes we add a phosphate to turn a process on or
turn a protein on to activate a signal transduction pathway.
And sometimes the phosphorylation, on occasion, will
end up phosphorylating a protein that shuts the system down.
Most often it's an activator though. So again to review
how ATP is formed. We take an adenosine diphosphate,
we add a little bit of energy, and the phosphate
molecule is attached. And then we can dephosphorylate,
remove the phosphate. Release some energy that's usable
to run our bodies system or cellular processes
and form ADP. So this is an ongoing cycle. And we'll
visit it many other times throughout this course.
So just as we could phosphorylate ADP and make it ATP,
we can also phosphorylate proteins. And this is what
happens a lot in our signal transduction cascades in
order to elicit cellular effects. So in this case
we have a protein kinase perhaps and ATP or perhaps
even GTP might come in and drop off a phosphate
and attach it to the protein and itself leave as ADP.
So we've now phosphorylated some sort of protein.
Could be a protein kinase and we'll be examining
many of those in the future of this lecture.
So, once we have a protein phosphorylated,
it could actually go and activate a cascade,
a signal transduction pathway. Or it could run off
and shut down something. So maybe this protein grabs
on to another protein and prevents it having its action.
So phosphorylation could result in either a positive
effect on the signal transduction or a negative
effect. Shutting down effect of signal transduction.
These proteins can also be dephosphorylated, right.
Removing the phosphate group. And the enzyme
that removes the phosphate group would be called
protein phosphatase. -ase again is an enzyme.
So it's going to remove the phosphate so that that
phosphate could be recycled and added perhaps
to another protein. Generally the molecule
that's going to add phosphates is ATP.
However we will also see GTP coming into play because
we have this G-protein modulated responses.