Mitochondrial metabolism

Schematic representation showing the steps within the mitochondria in which energy stored in fatty acids, pyruvate, and amino acids is transformed into ATP. Energy substrates are first transported into the mitochondria where, after conversion into acetyl CoA, they enter the tricarboxylic acid cycle (TCA). The reduced forms of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) are formed from the citric acid cycle and the beta-oxidation of fatty acids in the mitochondrial matrix. Subsequently, oxidative phosphorylation or the respiratory chain, which is composed of four multi-subunit complexes (I, II, III, and IV) linked by the mobile electron carriers coenzyme Q and cytochrome c. The respiratory chain transfers electrons from NADH (via complex I) and from reduced flavoproteins (via complex II and electron transfer flavoprotein-coenzyme Q oxidoreductase [ETF-Qo]) to coenzyme Q10, then complex III, cytochrome c and finally complex IV, where they combine with molecular oxygen to form water.