glykogenogeneesiä

Glykogenogeneesiä is the metabolic process by which glycogen is synthesized from glucose. This process primarily occurs in the liver and muscles, serving as a way for the body to store excess glucose for later use. When blood glucose levels are high, such as after a meal, insulin is released, which stimulates glycogen synthesis.

The synthesis of glycogen involves several enzymatic steps. Glucose is first phosphorylated to glucose-6-phosphate, catalyzed by hexokinase in muscles and glucokinase in the liver. Glucose-6-phosphate is then isomerized to glucose-1-phosphate. This is the committed step in glycogen synthesis and is catalyzed by phosphoglucomutase. Glucose-1-phosphate is then activated by reacting with uridine triphosphate (UTP) to form uridine diphosphate glucose (UDP-glucose). This reaction is catalyzed by UDP-glucose pyrophosphorylase.

UDP-glucose is the direct precursor for glycogen synthesis. Glycogen synthase then transfers the glucose unit from UDP-glucose to the non-reducing end of an existing glycogen primer, forming an alpha-1,4 glycosidic bond. Since glycogen synthase cannot initiate a new glycogen chain, a primer molecule, typically a small protein called glycogenin, is required. Glycogenin acts as a starter, autoglycosylating itself with glucose units. Branching is introduced by glycogen branching enzyme, which transfers a segment of 6-7 glucose residues from the end of a chain to form an alpha-1,6 glycosidic bond, creating branches in the glycogen molecule. This branching increases the solubility of glycogen and provides more non-reducing ends for rapid synthesis and degradation.