One glycogen molecule can consist of long chains of 1,700 to 600,000 glucose units. About 0.5 percent of the weight of your muscles and 5 percent of the weight of your liver are made up of glycogen. Unlike glucose, glycogen is not soluble in water and cannot pass in and out of cells unless it is broken down into smaller, more soluble units. Its usefulness as a storage molecule is largely due to this insolubility. This is the reason of storing glucose in the body as glycogen.