The reactions of glycolysis convert glucose 6-phosphate to pyruvate. The entire process is cytosolic. Glucose 6-phosphate is reversibly isomerized to form fructose 6-phosphate. The physiologically irreversible phosphorylation of fructose 6-phosphate to form fructose 1,6-bisphosphate is catalyzed by phosphofructokinase. In a series of reversible reactions, fructose 1,6-bisphosphate is converted to two molecules of phosphoenolpyruvate each of which then reacts with ADP to form ATP and pyruvate in a physiologically irreversible reaction.