Different modes of operation of the pentose phosphate pathway

a. When the primary need is for nucleotide biosynthesis, the primary product is ribose-5-phosphate. Reducing equivalents from NADPH are used to reduce ribonucleotides to deoxyribonucleotide.

b. When the primary need is for reducing power (NADPH), fructose phosphates are reconverted to glucose-6-phosphate for reoxidation in the oxidative phase.

c. When only moderate quantities of pentose phosphates and NADPH are needed, the pathway can also be used to supply energy, with the reaction products being oxidized through glycolysis and the citric acid cycle.