Glykogenesiä

Glykogenesiä is the metabolic pathway that results in the synthesis of glycogen from glucose. This process primarily occurs in the liver and muscles, serving as a storage mechanism for glucose. When blood glucose levels are high, such as after a meal, insulin is released, signaling the body to store excess glucose as glycogen.

The process begins with glucose entering the cell and undergoing phosphorylation to glucose-6-phosphate, catalyzed by hexokinase or glucokinase. This step traps glucose within the cell. Glucose-6-phosphate is then converted to glucose-1-phosphate, a reaction catalyzed by phosphoglucomutase. Subsequently, glucose-1-phosphate is activated by reacting with uridine triphosphate (UTP) to form uridine diphosphate glucose (UDPG). UDPG is the direct precursor for glycogen synthesis.

Glycogen synthase is the key enzyme responsible for forming the alpha-1,4 glycosidic bonds that link glucose units together in the glycogen chain. It adds glucose residues from UDPG to a pre-existing glycogen primer. Since glycogen synthase can only extend existing chains, glycogenin, a protein, acts as the initial primer by catalyzing the addition of the first few glucose units to itself. Branching enzyme is then required to create alpha-1,6 glycosidic bonds, forming branches in the glycogen molecule, which increases its solubility and the number of non-reducing ends available for further synthesis and breakdown. This ensures efficient storage and rapid release of glucose when needed.