Question

Here are four problems (5 pts each) involving the calculation of DG°' for metabolic reactions we have discussed, based on experimentally determined redox potentials. Calculate the DG°' for each reaction using the equation DG°' = -nFDE₀' and the values for E₀' given in Table 1. Show your work and circle your answer.

Table 1. Reduction potentials for reduction half reactions:

1/2 O₂ + 2H⁺ + 2e^- ® H₂O                                              E₀' = +0.82 V

fumarate + 2H⁺ + 2e^- ® succinate                                  E₀' = +0.03 V

oxaloacetate + 2H⁺ + 2e^- ® malate                                 E₀' = -0.17 V

pyruvate + 2H⁺ + 2e^- ® lactate                                       E₀' = -0.19 V

a-ketoglutarate + CO₂ + 2H⁺ + 2e^- ® isocitrate               E₀' = -0.38 V

FAD + 2H⁺ + 2e^- ® FADH₂                                             E₀' = -0.22 V

NAD⁺ + 2H⁺ + 2e^- ® NADH + H⁺                                    E₀' = -0.32 V

CoQ + 2H⁺ + 2e^- ® CoQH₂                                            E₀' = +0.06 V

Problem 1. isocitrate + NAD⁺ ® a-ketoglutarate + CO₂ + NADH

Problem 2. succinate + FAD ® fumarate + FADH₂

Answer 1

Problem 1. isocitrate + NAD⁺---------> a-ketoglutarate + CO₂ + NADH

                 isocitrate ---------------> a-ketoglutarate + CO₂ + 2H⁺ + 2e^-                 E0 = 0.38V

                NAD⁺ + 2H⁺ + 2e^-------------> NADH + H⁺                                   E₀' = -0.32 V

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                     isocitrate + NAD⁺---------> a-ketoglutarate + CO₂ + NADH               E0 cell = 0.06V

                   G = -nE0cell *F

                              = -2*0.06*96500   = -11580J

Problem 2. succinate + FAD --------------->fumarate + FADH₂

                        succinate ------------------> fumarate + 2H⁺ + 2e-    E0 = -0.03V

               FAD + 2H⁺ + 2e^- ----------> FADH₂                                             E₀' = -0.22 V

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    succinate + FAD --------------->fumarate + FADH₂             E 0cell =- 0.25 V

                           G = -nE0cell *F

                                    = -2*-0.25*96500   = 48250J