Figure 1.

Major metabolic pathways. Glycolysis is a 10-step reaction that converts glucose into pyruvate; pyruvate is then converted into lactate or enters the tricarboxylic acid (TCA) cycle as acetyl-CoA to yield NADH and FADH₂. NADH and FADH₂ are used by the electron transport chain (ETC) to generate ATP. Metabolic intermediates derived from glycolysis can also be diverted to the pentose phosphate pathway (PPP) to generate NADPH and ribose-5-phosphate. Fatty acid synthesis occurs in the endoplasmic reticulum and requires both NADPH and ATP from other metabolic pathways. During periods of energy deprivation, fatty acids are metabolized in mitochondria via β-oxidation, yielding large amounts of NADH and FADH₂ for ATP synthesis in the ETC.