GRL-0617

Glycogen

Structure of Glycogen

Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. The polysaccharide structure represents the main storage form of glucose in the body.

Structure

Glycogen is a large, branched polymer of glucose residues. It is similar in structure to amylopectin, a component of starch, but is more extensively branched and compact. Glycogen is composed of _(1_4) glycosidic bonds with _(1_6) linkages occurring approximately every 8 to 12 glucose units, which create a highly branched structure.

Function

Glycogen functions as one of two forms of energy reserves, glycogen being for short-term storage and triglycerides (in adipose tissue) for long-term storage. Glycogen is stored primarily in the liver and muscle tissues. In the liver, glycogen can make up 5–6% of the organ's fresh weight, and the liver of an adult weighing 70 kg can store roughly 100–120 grams of glycogen. In skeletal muscle, glycogen is found in a much lower concentration (1–2% of the muscle mass), but the total amount exceeds that in the liver.

Metabolism

Glycogen metabolism involves two main processes: glycogenesis and glycogenolysis.

Glycogenesis

Glycogenesis is the process of glycogen synthesis, in which glucose molecules are added to chains of glycogen for storage. This process is activated during rest periods following the Cori cycle, in the liver, and also by insulin in response to high glucose levels.

Glycogenolysis

Glycogenolysis is the breakdown of glycogen to glucose-1-phosphate and glucose, which occurs in the liver and muscle tissues. This process is activated by the hormones glucagon and epinephrine (adrenaline) and is inhibited by insulin.

Clinical Significance

Disorders of glycogen metabolism can lead to various glycogen storage diseases, which are genetic disorders that affect the enzymes involved in glycogen synthesis or breakdown. These diseases can result in the accumulation or deficiency of glycogen in tissues, leading to a range of symptoms depending on the specific enzyme affected.

Related Pages

• Glucose
• Glycogenesis
• Glycogenolysis
• Glycogen storage disease
• Insulin
• Glucagon