Biochemistry, Glycogen

Glycogen is an extensively branched glucose polymer that animals use as an energy reserve. It is the animal analog to starch. Glycogen does not exist in plant tissue. It is highly concentrated in the liver, although skeletal muscles contain the most glycogen by weight. It is also present in lower levels in other tissues, such as the kidney, heart, and brain. The glucose residues within glycogen connect via two principal bonds, the alpha-1,4, and alpha-1,6 glycosidic bonds in linear strands and at junction points. The branching is a crucial aspect of glycogen as it increases its solubility and allows it to get metabolized more quickly. Importantly, glycogen serves to maintain glucose homeostasis in the animal body. Because of this, its metabolism is regulated primarily by insulin and glucagon and molecules in their downstream signaling pathways. Insulin and glucagon promote glycogen synthesis and breakdown, respectively. Pathologies that target enzymes involved in glycogen synthesis, degradation, and/or regulation may have significant adverse effects on the body.