Question

The standard reduction potential for coenzyme Q is 0.045 V, and the standard reduction potential for NAD is –0.32 V. Determine the theoretical number of ATP molecules that can be synthesized by the energy liberated from the oxidation of NADH by ubiquinone. The Faraday constant, I, is 96.48 kJ/V·mol. ΔG'° for ATP synthesis is +30.5 kJ/mol.

Answer 1

The relevant half reactions are as follows

            NAD⁺ + 2H⁺ + 2e^- -----> NADH + H⁺ E'^o = -0.32 V and,

            CoQ (UQ) + 2 H⁺ + 2 e^- ------> CoQH₂ (UQH₂), E'^o = +0.045V

Thus, CoQ is the electron acceptor and NADH is the electron donor.

ΔE'^o = E'^o (Acceptor) - E'^o(Donor) = +0.045 - (-0.32) = +0.365 V

The Faraday constant, F = 96.48 kJ/V·mol. ΔG'^o for ATP synthesis is +30.5 kJ/mol

The free energy change for a reaction is given by

ΔG = - n * F * ΔE'^o

ΔG  = - 2* 96.48 kJ/V·mol * 0.365 V = -70.43 KJ/mol

ΔG  = (-70.43 KJ/mol) * (0.75 ) = -52.82 KJ/mol

ΔG  = ΔG'^o + R*T ln[ATP]/[ADP][P_i]

[ATP]/[ADP] = [P_i] x e^{(ΔG - ΔG'o )/RT}

[ATP]/[ADP] = (1mM) x e^{(52.28-30.5)/2.48}

[ATP]/[ADP] = (1 x 10^-3) x e^8.78

[ATP]/[ADP] = 6.51