So Pyrophosphate is hydrolyzed into two orthophosphates and this drives the formation of UDP glucose. Now, once we have a bunch of these UDP glucose molecules, the enzyme we call glycogenin, not shown in this diagram, basically uses the UDP glucose molecules to generate a primer, a short sequence of glucose molecules that are linked by alpha one four glycocitic bonds. Because glycogen synthase needs that primer to begin the elongation process, to begin extending that glycogen. So now we take the UDP glucose. In the presence of the primer, the enzyme glycogen synthase basically increases or attaches this glucose onto that primer. In the process, we form a UDP molecule.