Glicogênese

Glicogênese is the metabolic pathway that results in the synthesis of glycogen from glucose. This process is primarily carried out in the liver and muscles. Glycogen is a branched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and some bacteria.

The primary hormone that stimulates glycogenesis is insulin, which is released by the pancreas in response to elevated blood glucose levels, typically after a meal. Insulin signals the body to store excess glucose as glycogen. The process begins with glucose entering the cell, usually facilitated by glucose transporters. Inside the cell, glucose is phosphorylated to glucose-6-phosphate. This step is catalyzed by hexokinase in most tissues and glucokinase in the liver and pancreas.

Glucose-6-phosphate is then isomerized to glucose-1-phosphate. Subsequently, glucose-1-phosphate is activated by reacting with uridine triphosphate (UTP) to form uridine diphosphate glucose (UDP-glucose). UDP-glucose is the direct precursor for glycogen synthesis. The enzyme glycogen synthase then transfers the glucose unit from UDP-glucose to a growing glycogen chain, forming an alpha-1,4 glycosidic bond. A branching enzyme introduces alpha-1,6 glycosidic bonds, creating the branched structure of glycogen, which allows for more rapid synthesis and breakdown.

The liver plays a crucial role in maintaining blood glucose homeostasis by storing and releasing glycogen. Muscle glycogen, on the other hand, serves as an immediate source of glucose for muscle contraction. When blood glucose levels drop, hormones like glucagon and epinephrine trigger glycogenolysis, the breakdown of glycogen back into glucose.