Learning Strategies in Biochemistry:
Mitochondrial Electron Transport and Oxidative Phosphorylation

Revised 2008/05/22

Essential Review:

From General Chemistry, review the following concepts:

  • Oxidation and reduction.
  • Electrochemistry, including the use of standard reduction potentials to calculate the standard cell potential for redox reactions.
  • The relationship between standard free energy change and standard cell potential.

Essential Memory Work:

Memorize, and make sure you know how to use, the following relationships and the terms they contain.

1)

2)

in which "red" refers to the electron acceptor (the species being reduced), "ox" refers to the electron donor (the species being oxidized), and E0' is the standard reduction potential of a species, as listed in a table of reduction potentials, usually in the chapter on introduction to metabolism.

Note carefully the following distinctions between terms:

  • DE0' is the standard cell potential, or the standard emf, a property of a redox reaction or of an electrochemical cell. Some texts call this the reduction potential difference, which is descriptively accurate, but not a standard term, like cell potential or emf.
  • E0' (without the delta) is the standard reduction potential, a property of a redox half-reaction or of a redox couple (or redox pair) like FAD/FADH2. It is not a property of a redox reaction.

Quiz (beginning of first class on electron transport)

Instructor will give you a balanced redox equation involving two of the redox couples in the table of reduction potentials in your text, and ask you to compute the standard cell potential (DE0') and the standard free-energy change (DG0') for the reaction. Be sure to notice that this task entails using the half reactions in the table to determine n, the number of electrons transferred in the reaction as written.

Sample Quiz

Determine DE0' (in volts) and DG0' (in kJ/mol) for the following reaction:

ubiquinone + 2 H+ + 2 cytochrome b (Fe2+) ----> ubiquinol + 2 cytochrome b (Fe3+)

Show equations used and calculations with all units.

Answers

  • DE0' = -0.04 V. Your value may differ slightly depending on the source of your reduction potentials.
  • DG0' = +8 kJ/mol. Electron transport from cytochrome b to ubiquinone is not spontaneous under standard condtions)
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