Question

why doesn't FADH produce as much ATP as NADH?

Answer 1

Ans. During ETC, FADH₂, because of having lower redox potential, is oxidized at complex II, then at III and IV successively. Oxidation of 1 FADH₂ translocate 6H⁺ from mitochondrial matrix (MM) to intermembrane space (IMS). So, 6H⁺ produce 1.5 ATP when they travel back to MM from IMS through ATP synthase.

# During ETC, NADH, is oxidized at complex I, then at III and IV successively. Oxidation of 1 NADH translocate 10H⁺ from mitochondrial matrix (MM) to intermembrane space (IMS). So, 10H⁺ produce 2.5 ATP when they travel back to MM from IMS through ATP synthase.

# The reason of difference in ATP yield is due to the standard redox potential of the two molecules. The standard redox potential of oxidation of NADH by O₂ through ETC is around 1.135 V whereas that of FADH₂ is around 1.034 V. A smaller value of standard redox potential of a reaction means a lower amount of Gibb’s free energy released (dG^0’ = -nFdE⁰)

# So, because of lower standard redox potential of FADH₂ oxidation, it produces less ATP than NADH.