In step two, we transform that glucose into an isomer called fructose. And in step three, we essentially take that fructose and we add another phosphate group onto that fructose. So let's focus on step one. So what exactly are the details of step one and why does it actually take place? So let's suppose we have a glucose on the outside of the cell, and in the membrane of that cell, there's a special type of membrane protein that we're going to focus on in a future lecture that actually transports that glucose into the cytoplasm of that cell. Now, once that glucose is inside the cytoplasm of that cell, a special type of enzyme, a protein kinase we call hexokinase, actually catalyzes the addition of a phosphoryl group from an ATP molecule onto the carbon number six of this glucose.