Hydrogens are frequently removed from nutrient substrates in bioenergetic pathways and are trans ported by "carrier molecules." Two biologically im portant carrier molecules are nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD). Both NAD+ and FAD transport hydrogens and their associated electrons to be used for later generation of ATP in the mitochondrion via aerobic processes.