Glycogen is the storage form of glucose in animals and humans
which is analogous to the starch in plants. Glycogen is synthesized
and stored mainly in the liver and the muscles. Structurally,
glycogen is very similar to amylopectin with alpha acetal linkages,
however, it has even more branching and more glucose units are
present than in amylopectin. Various samples of glycogen have
been measured at 1,700-600,000 units of glucose.
The structure of glycogen consists of long polymer chains
of glucose units connected by an alpha acetal linkage.
The graphic on the left shows a very small portion of a glycogen
chain. All of the monomer units are alpha-D-glucose, and all
the alpha acetal links connect C # 1 of one glucose to C # 4
of the next glucose.
The branches are formed by linking C # 1 to a C # 6 through
an acetal linkages. In glycogen, the branches occur at intervals
of 8-10 glucose units, while in amylopectin the branches are
separated by 12-20 glucose units.
Glycogen - Chime
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Acetal Functional Group:
Carbon # 1 is called the anomeric carbon and is the
center of an acetal functional group. A carbon that has two ether
oxygens attached is an acetal.
The Alpha position is defined as the ether oxygen being
on the opposite side of the ring as the C # 6. In the chair structure
this results in a downward projection. This is the same
definition as the -OH in a hemiacetal.
graphic of hemiacetal in a new window