NADPH production, ribose synthesis, and oxidative vs non-oxidative branches
The pentose phosphate pathway (PPP) runs parallel to glycolysis and has two branches. The oxidative branch irreversibly converts glucose-6-phosphate to ribulose-5-phosphate, generating 2 NADPH and 1 CO₂. The non-oxidative branch uses transketolase and transaldolase to interconvert sugar phosphates, allowing ribose-5-phosphate production without NADPH, or routing pentose phosphates back to glycolysis. The pathway is critical for NADPH-dependent reductive biosynthesis and for maintaining glutathione in its reduced (antioxidant) state — G6PD deficiency causes hemolytic anemia due to inability to regenerate GSH in red blood cells.