Although both hexokinase and phosphofructokinase catalyze irreversible steps in glycolysis and the hexokinase-catalyzed step is first, phosphofructokinase is nonetheless the pacemaker of glycolysis. What does this information tell you about the fate of the glucose 6-phosphate formed by hexokinase? Glucose 6-phosphate must be unstable and release its phosphoryl group over time. Glucose 6-phosphate must be utilized by other metabolic pathways. Glucose 6-phosphate must allosterically inhibit phosphofructokinase, but not hexokinase. Glucose 6-phosphate must be wasted when it is produced in excess.

Why is there such a large range of ∆G for the second step of glycolysis?

In the Cori cycle, the lactate product of glycolysis in muscle is transformedback into glucose by the liver. (a) List the enzymes involved in the lactate → glucose pathway. (b) What is the net gain/loss of ATP for one round of the Cori cycle (glucose → lactate → glucose)?

Two reactions are shown below. These reactions are directly coupled in cells by an enzyme called hexokinase, which is a key enzyme in glycolysis. It is generally the case that reactions that are directly coupled by enzymes share some common reactants. What is the net reaction when these two reactions are combined? Glucose + Inorganic Phosphate + ATP + Water → Glucose 6-phosphate + ADP Glucose + ATP + Water → Glucose 6-phosphate + ADP + Inorganic Phosphate Glucose + ATP → Glucose 6-phosphate + Inorganic Phosphate Glucose + ATP → Glucose 6-phosphate + ADP