Glycogen is a polysaccharide
composed of glucose units linked by
alpha 1-4 glycosidic bonds
, with occasional
alpha 1-6 glycosidic bonds
which provide branching points.
(Zoom in to view branching point/
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Each glycogen molecule may contain 60,000 glucose units, and
is about 8-12 glucose units in length, so that these molecules are bushy and nearly spherical in shape. The many exposed ends can have more glucose units added to them (glycogenesis) or removed from them (glycogenolysis). It is thus ideally suited for use as a short-term energy storage compound for excess glucose, which can also be quickly released for use in respiration,
Glycogen - also known as animal starch - is found in the liver and muscles. It is effectively similar in structure to the amylopectin fraction of starch, which has longer branches (24-30 glucose units).
This simple model - specifically prepared for this website by the Sweet program - shows a small section of a glycogen molecule consisting of 40 glucose units. The 1-4 linked sections can be seen to coil into a helical shape, and the two 1-6 linkages form helical branches away from the main section.
This helical structure is stabilised by hydrogen bonds between -OH groups on subsequent glucose units.