1. Starting Point: NADH starts its journey through the electron transport chain in complex I, also known as NADH-CoQ reductase. On the other hand, FADH2 enters the process later in complex II, also known as succinate dehydrogenase.
2. Number of Electrons Donated: NADH contributes two electrons to the chain when it transfers its reducing equivalents. In contrast, FADH2 delivers only two electrons, contributing fewer electrons compared to NADH.
3. Redox Partners: NADH passes its electrons to ubiquinone (CoQ), a small molecule that acts as a mobile electron carrier in the mitochondrial membrane. FADH2, on the other hand, transfers its electrons directly to the iron-sulfur protein of complex II.
4. Energy Yield: The transfer of electrons from NADH to CoQ allows complex I to pump four hydrogen ions (4H+) across the membrane, creating an electrochemical gradient. NADH provides more energy than FADH2 by facilitating this proton pumping, allowing for a greater contribution to the generation of ATP.
5. Path Through Complexes: NADH moves through complexes I, III, and IV of the electron transport chain. FADH2, after transferring its electrons in complex II, also joins the pathway in complex III and proceeds to complex IV.
These differences between NADH and FADH2 in terms of entry points, number of electrons delivered, redox partners, energy yield, and path through complexes contribute to the overall efficiency and regulation of the electron transport chain in cellular respiration.
