The glucose cycle (also known as the hepatic futile cycle) occurs primarily in the liver and is the dynamic equilibrium between glucose and glucose 6-phosphate. The liver is a vital organ in the human body and is present in Vertebrates and some other animals Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Glucose 6-phosphate (also known as Robison ester) is Glucose sugar Phosphorylated on carbon 6 This is important for maintaining a constant concentration of glucose in the blood stream. Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells €”such as nutrients and oxygen—and transports Waste products
Contents |
Function
The glucose cycle is required for one of the liver functions; the homeostasis of glucose in the blood stream. Homeostasis (from Greek: ὅμος hómos, "equal" and ιστημι istēmi, "to stand" lit When blood glucose levels are in excess, glucose can be stored in the liver as glycogen. Glycogen is a Polysaccharide of Glucose (Glc which functions as the secondary short term energy storage in Animal cells When glucose levels in the blood stream are low the glycogen can be catabolised and glucose may re-enter the blood stream. For the related metabolic process see Anabolism. Catabolism is the set of Metabolic pathways which break down molecules into
The catabolic process occurs at the nonreducing end of glycogen. A phosphate group breaks the bond between C 1 of a glucose ring and the O that connects it to the next(phosphorolysis). One glucose unit is thus splitted off. Glycogen (with n glucose units) is converted into G-1-P(a PO4 group now attaches to C1 where O used to ) and glycogen (with n-1 glucose units) by enzyme glycogen phosphorylase. G-1-P is then converted into G-6-P by enzyme phosphoglucomutase. A water molecule hydrolyses G-6-P to glucose, the enzyme is glucose-6-phosphatase.
Cell specificity
When glucose enters a cell it is rapidly converted to glucose 6-phosphate, by hexokinase. Variation across species Hexokinases have been found in every organism checked ranging from bacteria, Yeast, and Plants to humans and other Vertebrates The glucose cycle can occur in liver cells due to a liver specific enzyme glucose-6-phosphatase, which catalyse the dephosphorylation of glucose 6-phosphate back to glucose. Glucose 6-phosphatase (Glc-6-Pase is an Enzyme that hydrolyzes Glucose-6-phosphate resulting in the creation of a phosphate group and free glucose
Glucose-6-phosphate is the product of glycogenolysis or gluconeogenesis, where the goal is to increase free glucose in the blood due body being in catabolic state. Glycogenolysis (also known as "Glycogenlysis" is the Catabolism of Glycogen by removal of a Glucose monomer through cleavage with inorganic Gluconeogenesis (abreviated GNG) is a Metabolic pathway that results in the generation of Glucose from non- Carbohydrate carbon substrates such Other cells such as muscle and brain cells do not contain glucose 6-phosphatase. As a result, any glucose 6-phosphate produced in those cells is committed to cellular metabolic pathways, primarily pentose phosphate pathway or glycolysis.
Regulation of glucose cycle
Flux through the glucose cycle is regulated by several hormones including insulin and glucagon as well as allosteric regulation of both hexokinase and glucose 6-phosphatase. Insulin is a Hormone with intensive effects on both metabolism and several other body systems (eg vascular compliance Glucagon is an important Hormone involved in Carbohydrate metabolism. In Biochemistry, allosteric regulation is the regulation of an Enzyme or other Protein by binding an effector molecule at the protein's allosteric
Diseases associated with glucose cycle
A deficiency in glucose 6-phosphatase that disrupts the liver glucose cycle, can lead to von Gierke's disease
Glycogen storage disease type I ( GSD I) or von Gierke's disease, is the most common of the Glycogen storage diseases This Genetic diseaseDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic