Anabolic (amino acid metabolism and nucleotide biosynthesis) and catabolic reactions (glycolysis, TCA cycle, β-oxidation and amino acid oxidation) release electrons stored as FADH or NADH to the ETC that channel them to CoQ. In the picture is outlined the electron flux from the different enzymes of metabolic pathways to the complexes and super-complexes of the ETC. FADH₂ dependent enzymes attached to it, while NADH generated by a variety of metabolic process navigate to respiratory CI to be oxidized. Anabolic pathways are shown in green and catabolic pathways in red. The following pdb structures were used to develop this figure: 6idj (DHODH, Homo sapiens), 5m42 (proDH, Thermus thermophilus), 6iq6 (G3PDH, Homo sapiens), 6oi5 (SQOR, Homo sapiens), 2gmh (ETFDH, Sus scrofa), CI (5xtd, Homo sapiens), CII (4ytp, Sus scrofa), CIII2 (5xte, Homo sapiens), CIV (5z62, Homo sapiens), CIV2 (1occ, Bos taurus), ATPase (6tt7, Ovis aries), Tight N-respirosome (5j4z, Ovis aries) and lipidic bilayer (2mlr).