An 18-question problem with answers about the thermodynamics of a redox reaction in the electron transport chain.
1- Write a complete balanced redox reaction, wherein electron(s) are transferred between Coenzyme Q and lipoic/dihydrolipoic acid in a spontaneous forward direction. Indicate the states of all species on the reactant and product sides: ubiquinone or ubiquinol; lipoic acid or dihydrolipoic acid.
2-For the forward reaction, which species is acting as the oxidizing agent?
- ubiquinone
- ubiquinol
- lipoic acid
- dihydrolipoic acid
3- For the forward reaction, which species is acting as the reducing agent?
- ubiquinone
- ubiquinol
- lipoic acid
- dihydrolipoic acid
4-
a- Write the half-reaction involving ubiquinone.
b- For the overall redox reaction (Question #1), would this half-reaction occur as an oxidation or a reduction?
c- What is the value (in volts) of the standard reduction potential for this half-reaction?
5-
a- Write the half-reaction involving lipoic acid.
b- For the overall redox reaction (Question #1), would this half-reaction occur as an oxidation or a reduction?
c- What is the value (in volts) of the standard reduction potential for this half-reaction?
6- Calculate ΔE’° for the overall redox reaction (Question #1).
7- Does the calculated ΔE’° value (Question #6) supports the fact that the overall redox reaction (Question #1) would be spontaneous in the forward direction?
8- a- Calculate ΔG’° for the overall redox reaction.
b- Under standard biochemical conditions, is this reaction endergonic or exergonic?
9- Calculate K’eq for the overall redox reaction. Assume 25°C.
10- Calculate the actual free energy change, ΔG, if this redox reaction occurred within our cells (body temperature of 37°C) and typical cellular concentrations were as follows:
[ubiquinone] = 1.2 mM
[ubiquinol] = 5.3 mM
[lipoic acid] = 7.9 mM
[dihydrolipoic acid] = 2.5 mM
11- Calculate the actual change in potential, ΔE, if this redox reaction occurred within our cells (see conditions in Question #10).
12-
a- Calculate the enthalpy change (ΔH) associated with this redox reaction, assuming the conditions outlined in Question #10 and an entropy change (ΔS) of +0.8 kJ/mol∙K.
b- Is this reaction enthalpically favored or opposed?
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