Now I wanna spend a little bit time talking
about how we reverse all the process.
So a reversal of the process
happens with another hormone.
And that another hormone is one that we all
have heard about and that's insulin.
Insulin as we will see has the effect of countering
the entire epinephrine glucagon system.
Now insulin stimulates an enzyme called
phosphatase that I have mentioned earlier.
And what phosphatase does is it removes
phosphates from the glycogen enzymes.
This favors glycogen synthesis; because,
it was additional phosphate to the glycogen synthase that
inactivated it. So removing the phosphate will activate it.
Conversely we take the phosphate
off of glycogen phosphorylase
and we will have the effect of reducing its activity.
Insulin also stimulates the
uptake of glucose by cells
and this is important; because, blood glucose
can be hazardous for the body. So getting glucose
out of the blood and into the cells is important.
In this figure we can see a little bit
of the results of insulin action on cells.
We see in yellow that insulin binds to a receptor
of its own called the insulin receptor.
That binding to the insulin receptor, stimulates
several things to happen. Now, as I noted,
the liver cells, one of the things that happens, is that
they are stimulated to take up glucose from the blood stream.
The body treats glucose
like it's a poison.
In some ways it may well be a poison;
because, people who have trouble
maintain their blood glucose levels
have many problems. We know for example
the issues associated with diabetes.
So maintaining proper glucose levels is important
and insulin plays a role in that process.
We see insulin stimulates the movement
of a protein called glucose transporter-4
to the cell surface and so that green
dimer that you see on the cell surface has moved
there as a result of the insulin action.
The glucose is brought into
the cell when that happens
and you can see the glucose
Couple of things can happen with that. Glucose in the cell,
again, the cell is now gonna treat it like it is a poison.
The cell deals with that glucose in two ways.
One is it reduces the free glucose
concentration by making glycogen.
That takes glucose away out of the free system
and makes glycogen and glycogen is not a problem.
In addition glycolysis is favored
by the breakdown of glucose so that also has the
effect of reducing the glucose concentration.
Now the by product of glycolysis in breaking
down glucose is you make a lot of pyruvate.
If you are not getting plenty
of exercise what happens is
a lot of pyruvate gets
converted into acetyl-CoA,
and acetyl-CoA goes to fatty and you can
probably figure out where that's headed.
So when glucose levels are high
insulin decreases glucose concentration
by favoring glycogen synthesis, as I noted,
and by inhibiting glycogen breakdown.
So when glucose is needed, epinephrine does its
job and stimulates the release of glucose from glycogen.
And when glucose is abundant, insulin stimulates
the dephosphorylation of those same enzymes
to use the glucose in
either glycogen or glycolysis.
So maintaining sugar balance in
the body is an essential function.
And in this lecture we have seen
how glycogen metabolism is managed
to help the body to manage
its own glucose needs.
With these manage needs done properly,
the body functions having glucose when
necessary and being able to store
glucose when there is an excess.