Any consideration of sugar
metabolism must include discussion
of the ways in which sugar is
stored and released in the body.
In animals this is glycogen and
will be the subject of this talk.
In the first part of the talk what I will do
is go through a bit of the structural
and enzymatic considerations in the
breaking and making of glycogen.
And in the last part of the talk, I will discuss glycogen
from a regulatory point and how that regulation
helps the animal to meet its needs.
Now glycogen is a polymer of glucose, as I have
noted in another one of the presentations.
It is actually a very large polymer glucose
that you can see on the screen on the right.
Glycogen is stored in animals in liver and muscles.
In liver it is used to
provide a constant supply
of glucose into the blood
stream as the animal needs it.
And in muscles, it’s an immediate
source of glucose for the
contracting actions that muscles have to take.
Now glycogen is similar
to amylopectin of plants
and differs only in the amount of
branching that the molecule has.
Glycogen has branches about every
10 glucose residues. Whereas
amylopectin has branches about every 50 or so.
Glycogen helps to modulate blood glucose and it is;
because it is that battery or that storage form of glucose,
the liver can top up as necessary
to release blood glucose into blood
and allow that blood glucose
level to stay as needed.
Now glycogen in its synthesis
does not start with
the glucose, it actually starts
with a protein called glycogenin,
and to that protein is attached
the first glucose molecule.
And the attachment of that first glucose molecule
leads to the structure that you see here.
As you can see that this structure can be quite
complex with up to 20,000 glucose units
within a given glycogen entity.
Now this differs a bit from the plant storage glucose
forms which will have only order about 400 or so.