Electron transport system. Illustration of inner mitochondrial membrane reactions. From the NADH dehydrogenase complex, electrons are transported along a chain of proton pumping (H+) cytochrome electron-carrier protein complexes (pink). Reactions involve nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD). Oxygen (O2) is involved in the step leading to the ATP synthase complex (red). The final stage (pink, upper right) involves an ATP/ADP transporter that channels the energy carrying molecules ATP (adenosine triphosphate) and ADP (adenosine diphosphate). For this artwork with labels, see image C023/8805.