1. Fill in Table 1 to summarize what happens during electron transport as a result of oxidizing either NADH or succinate.

2. a. Write the sequence of complexes and coenzymes involved in oxidation of NADH.
b. Write the sequence of complexes and coenzymes involved in oxidation of succinate.

3. Assume O₂ is present, and FADH₂ can be oxidized by complex II.
a. What is the effect on electron transport of cyanide?
b. What is the effect on electron transport of rotenone?
c. What is the effect on electron transport of dinitrophenol (DNP)?

4. Cytochrome c (Fe³⁺) + e⁻ → cytochrome c (Fe²⁺)                              E°′ = 0.254 V
¹/₂ O₂ + 2 H⁺ + 2 e⁻ → H₂O                                                                  E°′ = 0.815 V
a. Write the whole reaction and explain its relevance to electron transport.
b. Calculate ΔE°′ and ΔG°′ for the spontaneous whole reaction.

5. a. How many electrons are transferred to Complex III for each NADH oxidized?
b. How many electrons are transferred to Complex III for each FADH₂ oxidized?
c. How many electrons are required to reduce one molecule of oxygen?
d. How many protons are transported from N to P as a result of the movement of 2 e⁻
     from Complex I to O₂?
e. How many protons are transported from N to P as a result of the movement of 2 e⁻
     from Complex II to O₂ ?

6. NAD⁺ + 2 H⁺ + 2 e⁻ → NADH + H⁺     E°′ = − 0.320 V
¹/₂ O₂ + 2 H⁺ + 2 e⁻ → H₂O           E°′ = 0.815 V
a. Write the whole reaction and explain its relevance to electron transport.
b. Calculate ΔE°′ and ΔG°′ for the spontaneous whole reaction.

Key

1.

2. a. NADH → Complex I → Coenzyme Q → Complex III → cyt c → Complex IV
   b. succinate → Complex II → Coenzyme Q → Complex III → cyt c → Complex I

3. a. Cyanide inhibits Complex IV, so oxidation of both NADH and FADH₂ would be inhibited; no ATP could be synthesized.
   b. Rotenone inhibits electron transfer in Complex I. Oxidation of NADH would be inhibited, but oxidation of succinate could still occur. Since [NADH] would increase, however, eventually reactions in the citric acid cycle would be inhibited.
    c. DNP is an uncoupler. Electron transport would still continue, with oxidation of both NADH and succinate; less ATP would be synthesized as a result.
You should understand the results of inhibition of a complex or of an uncoupler, but do not memorize the inhibitors.

4. a. 2 cyt c (Fe²⁺) + ¹/₂ O₂ + 2 H⁺ → 2 cyt c (Fe³⁺) + H₂O
     This is the whole reaction catalyzed by Complex IV during electron transport.
b. ΔE°′ = 0.561 V;
     ΔG°′ = − n F ΔE°′ = − (2) (96480 J/V-mole) (0.561 V) = − 108,251 J/mole

5. a. 2 e⁻ ;   b. 2 e⁻ ;   c. 4 e⁻ ;   d. 10 H⁺;   e. 6 H⁺

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