Now, the first step is known as phosphoralysis, and this process is catalyzed by an enzyme known as glycogen phosphorylase. Now, glycogen phosphorylase uses an orthophosphate molecule to actually cleave to break an alpha one four glycosytic bond between a terminal glucose molecule that contains a free hydroxyl group on the fourth carbon and the JSON glucose molecule. And this can be seen in the following picture. So we essentially have our first step of glycogen breakdown. So on the left side we have the reactant, the glycogen molecule that contains, let's suppose, N number of glucose molecules. And to simplify the diagram of only drawn two of these glucose molecules.