Glycogenolysis is the breakdown of the glycogen molecule into glucose, a simple sugar that the body uses for energy. Glycogen is essentially energy stored in the form of a long chain of glucose, and glycogenolysis occurs in muscle and liver cells when more energy needs to be produced. The opposite of glycogenolysis is glycogenesis, that is, the formation of glycogen from glucose molecules.
Function of Glycogenolysis
Glycogenolysis breaks down glycogen into glucose. In particular, the process of glycogenolysis forms one molecule of glucose-6-phosphate, while leaving the remaining glycogen chain with one less glucose molecule. This process is repeated many times in order to remove various glucose molecules from the chain. Glucose molecules are removed by phosphorolysis, i. H. break a molecular bond by adding phosphoric acid.
The central structure is the protein glycogen, while the branches are glucose chains. A single glycogen molecule can contain up to 30,000 bound glucose units.
Glycogenolysis occurs when levels of adenosine triphosphate (ATP), the energy molecule used in cells, are low (and blood sugar levels are low). Because glycogenolysis is a way of releasing glucose and glucose is used to make ATP, it occurs when energy is low and more energy is needed. Also, when ATP levels are high, glucogenesis occurs instead, as it is a way of storing energy.
Glycogen is stored in the muscles and the liver. It is estimated that glycogen stored in the liver makes up about 5 percent of the liver’s weight, while glycogen stored in the muscles makes up 1-2 percent of its weight. In myocytes, which are muscle cells, glucose provides the energy necessary for muscle movement. Glycogenolysis in hepatocytes or liver cells is slightly different. When glycogenolysis occurs in the liver, the glucose that is produced is not directly used by the liver. Instead, glucose enters the bloodstream for use by other cells. Glycogen from animals is similar to starch from plants; Starch is also a glucose chain that is used for energy storage in plants and can be broken down when a plant needs energy.
Regulators of Glycogenolysis
Glycogenolysis is maintained by hormones, and neural signals may also play a role in myocytes. Blood levels of the hormones glucagon and insulin rise and fall respectively, which affects whether or not glycogenolysis occurs. Glycogenolysis is also involved in the fight or flight response, the instinctive response of an animal to fight or flee from an adversary. In stressful or threatening situations, the fight or flight response is activated and the hormone adrenaline (adrenaline) is formed. Adrenaline stimulates glycogenolysis as the body needs the energy to fight or flee. It also inhibits glycogenesis as the body uses energy rather than storing it during a fight or flight response. If a fight or flight response does not occur (such periods are sometimes called “rest and digest”), glycogenesis repeats, and glycogenolysis is inhibited.
Enzymes Involved in Glycogenolysis
Several enzymes are involved in glycogenolysis. Enzymes are proteins that allow chemical reactions to occur. An enzyme that plays a role in glycogenesis is glycogen phosphorylase. Breaks the bond between glucose and glycogen by replacing a phosphoryl group, PO32-.
At this point, the glucose separated from glycogen is glucose-1-phosphate. The enzyme phosphoglucomutase converts it to glucose-6-phosphate, the form cells use to make ATP. The glycogen debranching enzyme transfers all but one of the remaining glucose molecules from one glycogen branch to another. Finally, ɑ [1 → 6] glucosidase removes the last glucose molecule that gets rid of this branch of glucose molecules.
Difference Between Glycogenesis and Glycogenosis
As mentioned above, glycogenesis is the opposite of glycogenolysis; is when glycogen is made from glucose. However, there is also glycogenosis, which has a very similar spelling but is a completely different term. Glycogenosis, better known as glycogen storage disease (GSD), is a genetic disorder in which the process of glycogen formation (glycogenesis) or the breakdown of glycogen (glycogenolysis) is disrupted. There are 11 different types of GSD, and about 1 in 20,000 to 25,000 people in the United States is born with some form of GSD. Some types are relatively milder than others. Type II GSD is particularly serious and leads to death within two years of birth. Other types include growth retardation and/or movement intolerance.
Glycogenolysis definition, Function of Glycogenolysis