Biochemistry Revision Questions — Electron OmpathStudy

Biochemistry Revision Questions — Electron Transport Chain & Redox (Past Paper) Short-answer revision questions on the electron transport chain, redox potentials and oxidative phosphorylation. Questions only — no answer key. --- 1. The table below demonstrates the sequence of electron carriers in a plant ETC: Reduced form Oxidized form E'o (V) --- --- --- Cytochrome b6 (Fe2+) Cytochrome b6 (Fe3+) -0.06 Cytochrome f (Fe2+) Cytochrome f (Fe3+) +0.365 Ferredoxin (reduced) Ferredoxin (oxidized) -0.432 Ferredoxin-reducing substrate (reduced) Ferredoxin-reducing substrate (oxidized) -0.60 Plastocyanin (reduced) Plastocyanin (oxidized) +0.40 a) Predict the probable sequence of these electron carriers in this ETC, based on their E'os. b) Draw an accurate energy diagram analogous to the one given in class (page/slide 69). c) Which step(s) in this chain is/are unlikely to yield sufficient free energy to generate a molecule of ATP per pair of electrons transferred? Justify your answer. 2. The following equation is a sum reaction of electron flow from NADH to oxygen in the ETC: NADH + H⁺ + ½O₂ = NAD⁺ + H₂O a) Calculate the value of ΔE'o for the net reaction. b) Calculate the ΔG°′ for this reaction. c) How many ATPs can be theoretically generated? Justify your answer. 3. The 3 reactions below are catalyzed by the NADH-DH complex (revise the ETC): (i) NADH + H⁺ + E–FMN → NAD⁺ + E–FMNH₂ (ii) E–FMNH₂ + 2H⁺ + Q → E–FMN + 2Fe²⁺ + 2H⁺ (iii) 2Fe²⁺ + 2H⁺ + Q → 2Fe³⁺ + QH₂ NET: NADH + H⁺ + Q → NAD⁺ + QH₂ For each of the 3 reactions, identify: a) the electron donor b) the electron acceptor c) the conjugate redox pair d) the reducing agent e) the oxidizing agent 4. The standard reduction potentials of the NAD⁺/NADH and Pyruvate/Lactate conjugate pairs are -0.32V and -0.19V respectively. a) Which conjugate pair has the greater tendency to lose electrons? Explain. b) Which is the stronger oxidizing agent? Explain. c) If you begin with 1M concentrations of each reactant and product at pH 7.0, in which direction will the following reaction proceed — forwards (to the right) or in reverse? Explain. Pyruvate + NADH + H⁺ = Lactate + NAD⁺ d) What is the ΔG°′ for this reaction, taking the number (n) of electrons to be 2? 5. Use the table below to answer questions (a)–(d): Oxidant Reductant n E'o (V) --- --- --- --- NADP⁺ NADPH + H⁺ 2 -0.32 Oxidized glutathione (GSSG) Reduced glutathione (GSH) 2 -0.23 ½O₂ + 2H⁺ H₂O 2 +0.82 a) Write an equation for the oxidation of reduced glutathione (GSH) by O₂. b) Write an equation for the reduction of O₂ by reduced glutathione. c) Calculate the ΔE'o and ΔG°′ for this reaction. d) What is ΔE'o and ΔG°′ for the reduction of oxidized glutathione (GSSG) by NADPH? 6. When dicyclohexylcarbodiimide (DCCD) is added to a suspension of tightly coupled, actively respiring mitochondria, the rate of electron transfer (measured by oxygen consumption) and the rate of ATP production (oxidative phosphorylation) dramatically decrease. If a solution of 2,4-Dinitrophenol (2,4-DNP) is now added to the preparation, oxygen consumption returns to normal but ATP production remains inhibited. From your knowledge of the ETC and oxidative phosphorylation (OP), answer the following: a) Which of the two (ETC or OP) is affected by DCCD? b) Why does DCCD affect oxygen consumption of mitochondria? c) Explain the effect of 2,4-DNP on the inhibited mitochondrial preparation. d) Which of the following inhibitors does DCCD most resemble in its action: Antimycin A, Oligomycin or Rotenone? Explain. --- Source: biochemistry/questions/revision questions.pdf.