Glycogen is a polymer, a molecule typically made up of residues of glucose, a sugar used by the body as energy. The polymer is usually the body’s main carbohydrate storage; it can provide glucose when it is necessary as well as store sugar when it builds up in the blood. Glycogen biosynthesis on a molecular level generally involves a compound called Uridine Diphosphate (UDP) glucose. An activated form of the sugar, UDP glucose is produced from another substance called Glucose 1-Phosphate (G1P) in a reaction triggered by a specific enzyme.
While glycogen is made directly from UDP glucose, it is broken down into G1P in one step, a difference that typically contributes to biological energy efficiency. An enzyme typically allows the molecule to keep growing. The branching of the molecule during glycogen biosynthesis is controlled by another enzyme, and occurs after several glucosyl elements are linked to it. Structurally, glycogen is normally capable of being stored in body fluids, which means it is soluble until a reaction triggers it to be broken down for use as energy. Phosphate molecules are used to break it down and the branches enable this process to occur faster than otherwise.
The liver is typically responsible for glycogen biosynthesis, and can monitor the levels of glucose in the bloodstream. While glucose is generally used by muscles, it is not produced in these tissues, so enzymes responsible for its biosynthesis are usually only found in the liver. In contrast to other types of biosynthesis, water is not normally used to break down glycogen. To disassemble the molecule, phosphate typically works with other enzymes, which are present in other varieties to help prevent glycogen from forming and breaking down at the same time.
If glucose builds up faster than necessary, this can be regulated by the liver, however the states of the molecule are controlled by an enzyme called phosphorylase kinase. This enzyme can be activated by another or by calcium, which is generally essential for muscles to contract. Glycogen biosynthesis, therefore, is often closely associated with muscle activity. There are also enzymes present in muscle that can determine whether the molecule is active to inactive.
Other compounds usually important in glycogen biosynthesis are Adenosine Triphosphate (ATP) molecules, which are involved the storage of energy as well. Insulin is a hormone normally released when glucose levels in the blood are high. It can interact with enzymes to stimulate glycogen biosynthesis and inhibit the molecule’s break down. Various diseases can affect how glycogen is synthesized, stored, and used by the body.