Passage
Catabolism is an oxidative process in which electrons are transferred from lipids, proteins, and carbohydrates to generate high-energy electron carriers from nicotinamide adenine dinucleotide (NADH/NAD⁺) and flavin adenine dinucleotide (FADH₂/FAD) . Both are used in the electron transport chain (ETC) as electron providers in a series of reactions. The transfer of electrons provides energy that drives oxidative phosphorylation and the production of ATP. Reduction of NAD⁺ proceeds according to the following half-reaction:
Reaction 1Reactions in the ETC occur in four protein complexes (I-IV) located in the inner mitochondrial membrane. Here high-energy electrons are shuttled from complexes I, II, and III to complex IV, where O₂ serves as the final electron acceptor. The net result of NADH oxidation is described by Reaction 2.
NADH+H++12O2→NAD++H2OReaction 2At complexes I, III, and IV, hydrogen ions move from the mitochondrial matrix to the intermembrane space and create the electrochemical gradient, or proton motive force (pmf) , that drives ATP synthesis. Each NADH molecule drives the net pumping of 10 protons across the membrane, as per Reaction 3.
NADH+11H++12O2→NAD++10H++H2OReaction 3
Adapted from Garrett R, Grisham CM, Sabat M. Biochemistry. Cengage Learning; 2011.
-The reduction half-reaction for oxygen is What is the overall reduction potential for the ETC?

Question

Passage
Catabolism is an oxidative process in which electrons are transferred from lipids, proteins, and carbohydrates to generate high-energy electron carriers from nicotinamide adenine dinucleotide (NADH/NAD⁺) and flavin adenine dinucleotide (FADH₂/FAD) . Both are used in the electron transport chain (ETC) as electron providers in a series of reactions. The transfer of electrons provides energy that drives oxidative phosphorylation and the production of ATP. Reduction of NAD⁺ proceeds according to the following half-reaction:

Reaction 1Reactions in the ETC occur in four protein complexes (I-IV) located in the inner mitochondrial membrane. Here high-energy electrons are shuttled from complexes I, II, and III to complex IV, where O₂ serves as the final electron acceptor. The net result of NADH oxidation is described by Reaction 2.

NADH+H++12O2→NAD++H2OReaction 2At complexes I, III, and IV, hydrogen ions move from the mitochondrial matrix to the intermembrane space and create the electrochemical gradient, or proton motive force (pmf) , that drives ATP synthesis. Each NADH molecule drives the net pumping of 10 protons across the membrane, as per Reaction 3.

NADH+11H++12O2→NAD++10H++H2OReaction 3
Adapted from Garrett R, Grisham CM, Sabat M. Biochemistry. Cengage Learning; 2011.
-The reduction half-reaction for oxygen is

What is the overall reduction potential for the ETC?

Quizplus · Accepted Answer

11ecba2d_119e_62a8_a3bf_210866c9b6d9_MD0008_00 To find the overall reduction potential for a particular redox couple, subtract the standard reduction potential for the reducing agent (electron donor) from that of the oxidizing agent (electron acceptor). The passage states that O₂ is the final electron acceptor, so in this scenario the overall reduction potential (ΔE₀′) is calculated as the standard reduction potential of oxygen (0.816 V) minus the standard reduction potential of NAD⁺ (−0.320 V): (0.816 V) − (−0.320 V) = 1.136 V ≈ 1.14 V Alternately, the two half-reactions may be added to produce the full reaction: 11ecba2d_119e_62a9_a3bf_67388034443c_MD0008_00 Notice that the half-reaction involving the electron donor (NADH) must be flipped so that NADH is on the left; consequently, the sign of the reduction potential for that half-reaction must be changed from negative to positive. (Choice A) This value, which is the correct magnitude but the wrong sign, would be the correct potential for the reverse reaction in which electrons are transferred from H₂O to NAD⁺. (Choices B and C) Omitting the negative sign before −0.32 V results in an answer of 0.50 V. If the sign is omitted and the electron donor and acceptor are reversed, then the answer becomes −0.50 V. Educational objective: The overall reduction potential of a redox pair is the difference in standard reduction potentials of the oxidizing and reducing agents. This value indicates how likely a particular compound is to gain or lose electrons. More positive values indicate a tendency to accept electrons, and more negative values indicate a tendency to lose electrons.

Passage Catabolism Is an Oxidative Process in Which Electrons Are Transferred