Homework for Electron Transport and the Proton Motive Force in
Mitochondria (Due, 9/13/10)
1. In complex I (NADH-Co Q Reductase) electrons are transported from NADH
to Co Q.
(A) Write the reaction for this electron transport
NADH + CoQ  NAD+ + CoQH2
(B) Calculate ΔEo for this reaction [use values in Karp, p. 194]
NAD+  NADH; Eo = - 0.32V
CoQ  CoQH2; Eo = + 0.045V
ΔEototal= Eored - Eoox = + 0.045 - (- 0.32) = + 0.37V
(C) Based on this ΔEo, calculate ΔG.
ΔGo = -nFΔEo = -2(23.06) (0.37) = - 17.1 kcal/mol
(D) Can this ΔG be coupled to ATP synthesis? Explain
Yes because the free energy released greatly exceeds the amount of ΔGo
needed to synthesized ATP from ADP: ADP + Pi  ATP (+7.5 kcal/mol)
2. In complex IV (cytochrome c oxidase) electrons are transported from
cytochrome a3 to O2.
(A) Write the reaction for this electron transport
½ O2 + cyt a3red  cyt a3ox + H2O
(B) Calculate ΔEo for this reaction [use values in Karp, p. 190 or 194]
2 cyt a3ox  2 cyt a3red ; Eo = + 0.385 V
½ O2  H2O;
Eo = + 0.816 V
ΔEototal = Eored - Eoox = 0.816 - (+ 0.385) = + 0.43 V
(C) Based on this ΔEo, calculate ΔG.
ΔGo = -nFΔEo = -2(23.06) (0.43) = - 19.8 kcal/mol
(D) Can this ΔG be coupled to ATP synthesis? Explain.
Yes because the free energy released greatly exceeds the amount of ΔGo
needed to synthesized ATP from ADP: ADP + Pi  ATP (+ 7.5 kcal/mol)
3. Suppose that two components of an electron transport chain
cytochromes x and y have Eo values of + 0.4 and +0.3, respectively.
(A) In what direction do electrons flow between these two components?
cyt y  cyt x
(B) What is the Δ Eo for this reaction?
ΔEototal = Eored - Eoox = +0.4 - (+0.3) = + 0.10 V
(C) Based on this Δ Eo, what is the Δ G for this reaction?
ΔGo = -nFΔEo = -2(23.06) (0.10) = - 4.61 kcal/mol
(D) Can this ΔG be coupled to ATP synthesis? Explain.
No the ΔGo is too small. At least – 7.5 kcal/mol is required
4. (A) Calculate the proton motive force (pmf) across a mitochondrial inner
membrane where the electrical potential across the membrane, ψ = -100
mV and the Δ pH = 0.1.
Δp = ψ -59 Δ pH = -100 mV - 59(0.1) = -100 - 5.9 = -106 mV = - 0.106 V
(B) What is the Δ G for the movement of a proton down this proton generated
gradient?
ΔGo = zFΔp = (23.06) (- 0.106 V) = - 2.44 kcal/mol
(C) How many protons would have to be transported down this proton
gradient to generate enough Δ G for the synthesis of ATP from ADP?
Explain.
Based on a ΔGo of +7.5 kcal/mol for ADP  ATP, it would take a minimum of
3 protons and likely 4 or 5 for synthesis of 1 ATP