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Electron Transport Chain.

Rank the following redox-active coenzymes and prosthetic groups of the electron-transport chain in order of increasing electron affinity. Each species must be matched with a different number ranking.

cytochrome a
coenzyme Q
FAD
cytochrome c
NAD+

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Rank the following redox-active coenzymes and prosthetic groups of the electron-transport chain in order of increasing electron affinity. Each species must be matched with a different number ranking.

cytochrome a
coenzyme Q
FAD
cytochrome c
NAD+

Solution: In order to answer this question, we must know the standard reduction potentials for these electron carriers. You can look these up in a table without any problem. Here they are:

cytochrome a E'° = 0.290 V
coenzyme Q E'° = 0.100 V
FAD E'° = -0.219 V
cytochrome c E'° = 0.254 V
NAD+ E'° = -0.320 V

The carriers that have the greatest positive E'° will have the greatest electron affinity. Remember, electrons flow from the half-reaction having the more negative standard reduction potential to the one having the more positive standard reduction potential. Therefore, the highest electron affinity is with cytochrome a and the lowest electron affinity is with NAD+. (You can put the rest in order.) This all makes perfectly good sense since the order of increasing electron affinity equates with the order of the carriers in the electron transport chain. You start with NAD+ and FAD. Then the electrons go to ...

Solution Summary

The solution ranks redox-active coenzymes and prosthetic groups of the electron-transport chain in order of increasing electron affinity.

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