Figure 50.18 Insulin Controls Glucose Traffic in the Liver Glucose freely enters and leaves liver cells by diffusion. But, when insulin is present (green arrows), glucose is phosphorylated and cannot leave the cell. The glucose 6-phosphate either enters glycolysis or is synthesized into glycogen. Insulin activates the enzymes of glycogen synthesis. Without insulin (red arrows) glucokinase is inhibited and glycogen phosphorylase and glucose phosphatase are activated. Thus glycogen is broken down to glucose phosphate, which is dephosphorylated so that it can leave the cell and enter the blood. Other monosaccharides—galactose and fructose—can also diffuse into the cell and be converted to glucose through these pathways.