Homework for Electron Transport and the Proton Motive Force in Mitochondria (Due, 9/13/10)

1. 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. • Write the reaction for this electron transport • NADH + CoQ NAD+ + CoQH2 • 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 • 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. 2. In complex IV (cytochrome c oxidase) electrons are transported from cytochrome a3 to O2. • Write the reaction for this electron transport • ½ O2 + cyt a3red cyt a3ox + H2O • 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 • 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. 3. Suppose that two components of an electron transport chain cytochromes x and y have Eo values of + 0.4 and +0.3, respectively. • 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. 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 • 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 • 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