Question

(5 points) For the Complex III in the electron transport chain:

Complex III step 1: UQH2 is oxidized in a 2 electron process. Cytochrome c is reduced and UQ is reduced to UQH in two 1 electron processes.
Complex III step 2: UQH2 is oxidized in a 2 electron process. Cytochrome c is reduced and UQH is reduced to UQH2 in two 1 electron processes.
The necessary standard reduction potentials are:
UQ + 2H+ + 2e- UQH2 E° = 0.06 V
cyt c (Fe3+) + e- cyt c (Fe2+) E° = 0.254 V
UQ + H+ + e- UQH. E° = 0.03 V
UQH. + H+ + e- UQH2 E° = 0.19 V
Calculate the total redox potential of the complex.
(5 Points) Now calculate how many moles of protons can be translocated across the inner mitochondrial membrane if translocation of 1 mole requires 23 kJ.
(5 Points) Calculate the free energy available for proton translocation assuming a 2electron process for each complex.

Answer 1

Step 1:

UQH2 + 2 cyt c (Fe3+) → UQ + 2 cyt c (Fe2+)

This step involves the oxidation of UQH2 and reduction of cyt c (Fe3+). The net reaction involves a 2-electron transfer from UQH2 to cyt c (Fe3+).

The standard reduction potential for UQH2 to UQ is given as 0.06 V, and for cyt c (Fe3+) to cyt c (Fe2+) it is 0.254 V.

The net standard reduction potential for step 1 can be calculated as follows:

E°_net1 = E°(UQH2) - E°(cyt c (Fe3+))

E°_net1 = 0.06 V - 0.254 V

E°_net1 = -0.194 V

Step 2:

UQH2 + 2 cyt c (Fe3+) → UQH + 2 cyt c (Fe2+)

This step also involves the oxidation of UQH2 and reduction of cyt c (Fe3+). The net reaction involves a 2-electron transfer from UQH2 to cyt c (Fe3+).

The standard reduction potential for UQH2 to UQH is given as 0.19 V.

The net standard reduction potential for step 2 can be calculated as follows:

E°_net2 = E°(UQH2) - E°(cyt c (Fe3+))

E°_net2 = 0.19 V - 0.254 V

E°_net2 = -0.064 V

Total redox potential of Complex III:

To calculate the total redox potential, we sum up the net reduction potentials of step 1 and step 2:

E°_total = E°_net1 + E°_net2

E°_total = -0.194 V + (-0.064 V)

E°_total = -0.258 V

Now, let's calculate the free energy available for proton translocation assuming a 2-electron process for each complex.

The equation relating free energy change (ΔG) and standard reduction potential (E°) is given by:

ΔG = -nFΔE°

Where:

ΔG is the free energy change

n is the number of electrons transferred

F is Faraday's constant (96,485 C/mol)

ΔE° is the standard reduction potential

For a 2-electron process, n = 2.

ΔG1 = -2 * 96,485 C/mol * (-0.194 V)

ΔG1 = 37,508.12 J/mol

ΔG2 = -2 * 96,485 C/mol * (-0.064 V)

ΔG2 = 12,303.04 J/mol

Therefore, the free energy available for proton translocation for each complex is 37,508.12 J/mol for Complex III, step 1, and 12,303.04 J/mol for Complex III, step 2.

To calculate the moles of protons translocated, we can use the equation:

ΔG = nFΔp

Where:

ΔG is the free energy change in joules

n is the number of moles of protons

F is Faraday's constant (96,485 C/mol)

Δp is the potential difference finish up now