What would happen if the NAD^+-dependent enzymes of the citric acid cycle were l

Question

What would happen if the NAD^+-dependent enzymes of the citric acid cycle were linked to the electron transport chain with enzymes containing FAD as a cofactor. instead NAD^+? The standard reduction potentials are: NAD^+ + 2H^+ + 2e^- rightarrow NADH + H^+ E_o ' = -0.32 V FAD + 2H^+ + 2e^- rightarrow FADH_2 E_o ' = +0.31 V 1/2 O_2 + 2H^+ + 2e^- rightarrow H_2 O E_o '= +0.82 V ATP would be synthesized faster because FADH_2 is closer to oxygen in the electron-transport chain. Less ATP would be made because FADH_2 rightarrow O_2 yields only about half of the standard free energy change compared with NADH rightarrow O_2. More ATP would be made because FADH_2 rightarrow O_2 yields about twice the standard free energy change compared with NADH rightarrow O_2. ATP would be synthesized slower because FADH_2 has a higher activation barrier than NADH. none of these

Explanation / Answer

Answer

Less ATP would be made

Because one FADH2 yield only 1.5 ATPs upon oxidation by electrion transport chain (ETC), whereas NADH+H+ yields 2.5 ATPs

Upon the oxidation of FADH2 by ETC, 6 protons are transported from mitochondrial matrix into the intermembrain space. However, 10 protons are transported upon the oxidation of NADH+H+

4 protons are required to synthesis one ATP

therefore, ATP generation would be less in case of FADH2

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