Glycogen is a polysaccharide consisting of glucose. It is a branched polymer — that means it is not linear/straight but has long chains of glucose coming off the sides of another glucose chain.
Animal cells store glucose in the form of glycogen. After eating, glucose levels in the blood increase, causing insulin to be released. Glucose is then taken up by muscle and liver cells, and converted into glycogen granules (glycogenesis).
When energy is needed (exercise), or when blood sugar levels are low (between meals/fasting), glycogen is broken back down into glucose for use, or released back into the blood.
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