the process of breaking down glycogen to glucose is an example of glycogenolysis.
the process of breaking down glycogen to glucose is an example of glycogenolysis.
the process of breaking down glycogen to glucose is an example of?
glycogenolysis
plasma glucose is said to be maintained when there is an equal rate of glucose appearance (entry into the blood) and glucose disposal (removal from the blood). in the healthy individual, the rates of appearance and disposal are essentially equal during exercise of moderate intensity and duration; however, prolonged exercise or sufficiently intense exercise can result in an imbalance leaning towards a higher rate of disposal than appearance, at which point glucose levels fall producing the onset of fatigue. rate of glucose appearance is dictated by the amount of glucose being absorbed at the gut as well as liver (hepatic) glucose output. although glucose absorption from the gut is not typically a source of glucose appearance during exercise, the liver is capable of catabolizing stored glycogen (glycogenolysis) as well as synthesizing new glucose from specific reduced carbon molecules (glycerol, pyruvate, and lactate) in a process called gluconeogenesis. the ability of the liver to release glucose into the blood from glycogenolysis is unique, since skeletal muscle, the other major glycogen reservoir, is incapable of doing so. unlike skeletal muscle, liver cells contain the enzyme glycogen phosphatase, which removes a phosphate group from glucose-6-p to release free glucose. in order for glucose to exit a cell membrane, the removal of this phosphate group is essential. although gluconeogenesis is an important component of hepatic glucose output, it alone can not sustain exercise. for this reason, when glycogen stores are depleted during exercise, glucose levels fall and fatigue sets in. glucose disposal, the other side of the equation, is controlled by uptake of glucose at the working skeletal muscles. during exercise, despite decreased insulin concentrations, muscle increases glut4 translocation of and glucose uptake. the mechanism for increased glut4 translocation is an area of ongoing research.
exercise physiology
glycogen branching enzyme is an enzyme that adds branches to the growing glycogen molecule during the synthesis of glycogen, a storage form of glucose. more specifically, during glycogen synthesis, a glucose 1-phosphate molecule reacts with uridine triphosphate (utp) to become udp-glucose, an activated form of glucose. the activated glucosyl unit of udp-glucose is then transferred to the hydroxyl group at the c-4 of a terminal residue of glycogen to form an α-1,4-glycosidic linkage, a reaction catalyzed by glycogen synthase. importantly, glycogen synthase can only catalyze the synthesis of α-1,4-glycosidic linkages. since glycogen is a readily mobilized storage form of glucose, the extended glycogen polymer is branched by glycogen branching enzyme to provide glycogen breakdown enzymes, such as glycogen phosphorylase, with a large number of terminal residues for rapid degradation. branching also importantly increases the solubility and decreases the osmotic strength of glycogen.
glycogen branching enzyme