2.1 Circle the correct underlined words describing biosynthesis of glycogen from glucose. (5 points)
UDP-glucose, the glucose donor in the biosynthesis of glycogen, is an activated form of glucose. The synthesis of activated glucose starts with the glucose transportation into cells by a membrane-bound protein, the glucose transporter/ glucose G-coupled protein. Glucose is then phosphorylated by hexokinase or glucokinase to give glucose-6-phosphate, which is isomerized to glucose-1-phosphate by phosphoisomerase/phosphoglucomutase. The enzyme UDPglucose pyrophosphorylase/ UDP-glucose kinase then catalyzes the synthesis of UDP-glucose. The reaction is drawn to the right by rapid enzymatic cleavage of pyrophosphate to orthophosphate, catalyzed by pyrophosphatase/pyrophosphatelyase. UDP-glucose is the immediate donor of a glucosyl residue to the nonreducing end of a glycogen branch, which must be at least four glucose residues in length. Glycogen synthase/glycogen transglycosylase is a glycosyltransferase-an enzyme that transfers an activated sugar unit to a nonreducing sugar hydroxyl group generating an \alpha (1->4) - glycosidic linkage.