Glucose cycle
The glucose cycle (also known as the hepatic futile cycle) occurs primarily in the liver and is the dynamic balance between glucose and glucose 6-phosphate. This is important for maintaining a constant concentration of glucose in the blood stream. Function The glucose cycle is required for one of the liver functions; the homeostasis of glucose in the blood stream. When the blood glucose level is too high, glucose can be stored in the liver as glycogen. When the level is too low, the glycogen can be catabolised and glucose may re-enter the blood stream. 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 split 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 changed to glucose 6-phosphate, by hexokinase or