Question

Cytochrome c oxidase receives electrons from reduced cytochrome c (cyt-c_red) and transmits them to molecular oxygen, with the formation of water. Write the chemical equation for this process, which occurs in an acidic environment. Calculate the cell voltage in the biological standard state.

Calculate ΔG°' (°' = biological standard state) for the previous reaction.

Calculate the equilibrium constant for the previous reaction.

Answer 1

(a) Chemical equation for this process, which occurs in an acidic environment:

Oxidation half cell: cyt-cred -> cyt-c + e^- ; E₀(cyt-c|cyt-cred) = +0.254 V
Reduction half cell: 1/2O₂ + 2H⁺ + 2e^- => H₂O;   E₀(H⁺|H₂O) = +0.815 V

Balanced redox reaction:

2cyt-cred + 1/2O₂ + 2H⁺ => 2cyt-c + H₂O .

No of electrons involved, n = 2

(b) Calculate the values of E^⊕ (E standard) cell, ΔG^⊕ (Standard delta G of reaction), and K for the reaction at 25°C.

(i) E^⊕ (E standard) cell = E₀cell = E0(H⁺|H₂O) - E₀(cyt-c|cyt-cred) = 0.815 - 0.254 = 0.561V

(ii) No of electrons involved, n =2

Charge of one mole of electron, F = 96500 C

ΔG^⊕ (Standard delta G of reaction) = DG0 = -n*F*E⁰_cell = -2*96500*0.561 = -108273 J/mole

(iii) At 25^oC,

E⁰_cell = 0.0591/n*Log(K)

Log(K) = E⁰_cell*n/0.0591 = 0.561*2/0.0591 = 19

K = 10¹⁹