Problems
6.1 In an electrochemical cell, where does an oxidation reaction occur?
6.2 Calculate the potential for the following reaction at 25°C using the following standard
potentials:
Zn(solid) +CuSO 4 (aqueous) ↔Cu(solid) +ZnSO 4 (aqueous)
Zn^2 ++2e−↔Zn(solid) Em=−0.76V
Cu^2 ++2e−↔Cu(solid) Em=+0.34V6.3 How is the midpoint potential of a protein related to its ability to oxidize another protein?
6.4 Assuming 100% efficiency and standard conditions, calculate how many photons, at 700 nm
or equivalently 2.8 × 1019 J, a chloroplast needs to absorb to make one ATP molecule from
ADP and inorganic phosphate.
6.5 What is the ratio between oxidized and reduced species when the potential is equal to the
midpoint potential?
6.6 If the typical energized thylakoid membrane has the estimated parameters of ΔV=0 mV,
[Pi] =0.01 M, and ΔpH =2.5 (out–in), and the proton/ATP stoichiometry is 4, what is the
ATP/ADP ratio? Use GATP° =8 kcal mol−^1.
6.7 If a protein has a midpoint potential of 125 mV, calculate the potential when the reduced/
oxidized ratio is (a) 10, (b) 1, and (c) 0.01.
6.8 Calculate the midpoint potential for a protein that was measured to have the following
redox data. The parameter Ris the ratio of the reduced form divided by the total amount
of protein. Use the table to guess which protein this is.
Potential (mV) R100 1.0
150 0.92
200 0.83
250 0.49
300 0.12
350 0.02
400 0.006.9 The standard free energy of hydrolysis of ATP is −30.5 kJ mol−^1. However, the concentrations
of ATP, ADP, and Piare not at standard conditions in the cell. Calculate the Gibbs energy
difference using concentrations of 2.25, 0.25, and 1.75 mM for ATP, ADP, and Pi.
6.10 Calculate the change in the Gibbs energy when condensation of Piwith ADP (ΔG=+30.5
kJ mol−^1 ) is coupled with cleavage of Pifrom phosphoenolpyruvate (ΔG=−61.9 kJ mol−^1 ).
6.11 Calculate the change in the Gibbs energy when ADP is formed from ATP, using the ΔG
values of −45.6 and −19.2 kJ mol−^1 for the first and second bond cleavages.
ATP +2H 2 O →AMP +2Pi