So we generate the UDP glucose and the Pyrophosphate. Now this reaction isn't really product favored. And to make it product favored to drive the formation of UDP glucose, the Pyrophosphate is cleaved by water into two orthophosphate molecules. 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.