Thus far, we have considered glycogen metabolism with a focus on energy production and storage. Another important fate for the ultimate breakdown product of glycogen degradation—glucose 6-phosphate—is as a substrate for the pentose phosphate pathway, a remarkably versatile set of reactions. The pentose phosphate pathway is an important source of NADPH, biosynthetic reducing power. Moreover, the pathway catalyzes the interconversion of the three- and six-carbon intermediates of glycolysis with five-carbon carbohydrates. These interconversions enable the synthesis of pentose sugars required for DNA and RNA synthesis as well as the metabolism of five-carbon sugars consumed in the diet.