The ultimate electron acceptor in the respiration process is molecular oxygen.
Electron transfer through the respiratory chain takes place through a complex
series of oxidationreduction reactions. Some of the electron transport steps
use iron-containing proteins called \(c y\) tochromes. All cytochromes transport
electrons by converting the iron in the cytochromes from the +3 to the +2
oxidation state. Consider the following reduction potentials for three
different cytochromes used in the transfer process of electrons to oxygen (the
potentials have been corrected for \(\mathrm{pH}\) and for temperature):
cytochrome \(\mathrm{a}\left(\mathrm{Fe}^{3+}\right)+\mathrm{e}^{-}
\longrightarrow\) cytochrome \(\mathrm{a}\left(\mathrm{Fe}^{2+}\right)\)
$$
\begin{array}{c}\mathscr{C}=0.385 \mathrm{~V}\end{array}
$$
cytochrome \(\mathrm{b}\left(\mathrm{Fe}^{3+}\right)+\mathrm{e}^{-}
\longrightarrow\) cytochrome \(\mathrm{b}\left(\mathrm{Fe}^{2+}\right)\)
$$
\begin{array}{l}\mathscr{E}=0.030 \mathrm{~V}\end{array}
$$
cytochrome \(\mathrm{c}\left(\mathrm{Fe}^{3+}\right)+\mathrm{e}^{-}
\longrightarrow \mathrm{cytochrome} \mathrm{c}\left(\mathrm{Fe}^{2+}\right)\)
$$
\begin{array}{c}\mathscr{C}=0.254 \mathrm{~V}\end{array}
$$
In the electron transfer series, electrons are transferred from one cytochrome
to another. Using this information, determine the cytochrome order necessary
for spontaneous transport of electrons from one cytochrome to another, which
eventually will lead to electron transfer to \(\mathrm{O}_{2}\).
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