Passage Catabolism Is an Oxidative Process in Which Electrons Are Transferred

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.
-Barbiturates are known to inhibit complex I but do not affect complexes II-IV.  Based on this fact, how will barbiturates affect the proton motive force?

A) The proton motive force increases.
B) The proton motive force decreases.
C) The proton motive force is unchanged.
D) The proton motive force becomes zero.

Correct Answer:

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