Question

Part of the Q-cycle within Complex III of the electron transport chain involves the transfer of a single electron from cytochrome bH to UQ. In the next round of the cycle, another single electron from cytochrome bH is passed to UQH·. Protons are harvested from the matrix.
[3] (a) Using Table 19.1, write the half reactions for these processes indicating the εo´ values
[2] (b) Write the overall net reaction
[5] (c) Calculate G°'overall for this process at 25°C

Answer 1

a) UQ + 2e-+ 2 H+ -- ----------------------->UQH2    E0 = 0.060 V

UQ + e- + H+ ------------------> . UQH         E0 = 0.030 V

. UQH + e- + H+ -----------> UQH2 E0 = 0.190 V

B) Net reaction

UQH2 + 2 H+(in) + 2 cyt ------> 4 H+ out + 2Cyt + UQ

C) The standard reduction potentials are between the NADH/NAD + (-0.315 V) and the oxygen/H2O (0.816 V)

They can be written as follows

NADH + H++ ½O2---------->NAD+ + H2O

NAD+ + 2e- + H+ --------->NADH                           Eo =−0.315 V

½O2+ 2e- + 2H+-------------->H2O                          Eo=+0.816 V

∆Eo =+0.816 - (- 0.315 V) = +0.816 + 0.315 V = 1.136 V

∆Go =−nFdelta Eo, where n = electrons transferred and F = Faraday's constant

=−219 kJ/mol,