Glycogen synthesis

The process of synthesizing glycogen from glucose (including a small amount of fructose and galactose) is called glycogen synthesis. The reaction is carried out in the cytoplasm and requires the consumption of ATP and UTP. The synthesis involves the following steps:
The glycogen synthase-catalyzed glycogen synthesis reaction cannot synthesize the first sugar molecule from the beginning, and requires α-1,4-polyglucose with at least 4 glucose residues as a primer to react with UDPG at its non-reducing end. The glucosyl group C1 on UDPG forms an α-1,4-glycosidic chain with the non-reducing terminal C4 of the glycogen molecule, so that the glycogen is increased by one glucose unit, and UDPG is a donor of active glucose-based, which consumes UTP during its formation, so Glycogen synthesis is a process of energy consumption, and glycogen synthase can only promote α-1,4-glycosidic bonds, so the enzyme catalyzes the reaction to form linear polysaccharide molecules such as starch which are composed of α-1,4-glycosidic bonds.
There is a special protein called glycogenin in the body, which can be used as a glucose-based receptor. From the beginning, it synthesizes the glucose of the first glycogen molecule. The enzyme that catalyzes this reaction is the glycogen-initiating synthetase, and then synthesizes The sugar chain acts as a primer and continues to catalyze the synthesis of sugar by glycogen synthase. At the same time, the formation of glycogen branched chains requires branch enzyme catalysis, and 5-8 glucose residue oligosaccharides are linearly linked to another sugar atom to be linked by α-1.6-glycosidic linkages to form branched sugar chains. The non-reducing end can continue to be catalyzed by glycogen synthase for elongation of the sugar chain. Multi-branched increases the water solubility of glycogen to facilitate its storage, and at the same time, when the glycogen is decomposed, it can start from multiple non-reducing ends at the same time, and increase the decomposition speed.