So for a single Fadh two that is synthesized during the citric acid cycle when we actually utilize and oxidize the Fadh two and two Fad we produce only two ATP molecules. But for the case of NADH that is formed within the mitochondrial matrix we form three ATPs per one NADH. So we conclude that NAD plus and Fad plus molecules are cofactor molecules that assist the enzymes involved in cellular respiration. Specifically, they assist the enzymes involved in the electron transport chain. So via the process of oxidative phosphorylation we basically synthesize our ATP molecules by moving these electrons across the electron transport chain and creating this electrochemical gradient. It's the electrochemical gradient that is used to drive the synthesis of ATP by this enzyme known as ATP synthase.