Generally speaking, no molecule supplies the energy to join a glucose into a growing glycogen chain. A previous step must be done and that is the formation of uridine diphosphate glucose (UDP-glucose or UDPG). Since the direct conversion of Glucose 1 phosphate (G1P) to glycogen and Pi is thermodynamically unfavorable (positive delta G) under all physiological Piconcentrations, glycogen biosynthesis requires the formation of UDPG by the combination of G1P with uridine triphosphate (UTP). UDPG's "high energy" status permits it to spontaneously donate glucosyl units to the growing glycogen chain. The step is catalyzed by the enzyme Glycogen Synthase, the glycosyl unit of UDPG is transferred to the C4-OH group on one of the glycogen's nonreducing ends to form an alpha(1-4)-glycosidic bond.