And both of these molecules are cofactors. That means they are non protein molecules that assist enzymes involved in cellular respiration. Now, what exactly is the purpose of these two molecules? Well, basically, they accept the high energy electrons that come from fuel sources that we ingest into our bodies, including sugars and fatty acids. So NAD plus and Fad plus molecules accept electrons and they carry these high energy electrons until the electron transport chain found in the inner mitochondrial membrane. And the electron transport chain uses these high energy electrons to synthesize ATP molecules.