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 \(\mathrm{O}_{2}\).

Step by step solution

01

List down the reduction potentials

We are given three reduction potentials for cytochromes: Cytochrome a: \(E_{a}=0.385 \mathrm{~V}\) Cytochrome b: \(E_{b}=0.030 \mathrm{~V}\) Cytochrome c: \(E_{c}=0.254 \mathrm{~V}\)

02

Arrange the cytochromes in order of increasing reduction potential

First, we need to arrange the three given cytochromes in order of increasing reduction potential: Cytochrome b: \(E_{b}=0.030 \mathrm{~V}\) < Cytochrome c: \(E_{c}=0.254 \mathrm{~V}\) < Cytochrome a: \(E_{a}=0.385 \mathrm{~V}\)

03

Determine the correct order for spontaneous electron transfer

For the electron transfer process to occur spontaneously, the final acceptor must have a more positive reduction potential than the initial donor. Therefore, the correct order for spontaneous electron transfer is Cytochrome b \(\rightarrow\) Cytochrome c \(\rightarrow\) Cytochrome a. This means that electrons are first transferred from Cytochrome b (with the lowest reduction potential) to Cytochrome c, and then from Cytochrome c to Cytochrome a (with the highest reduction potential). This order ensures that the electron transfer process occurs spontaneously and ultimately leads to the electron transfer to molecular oxygen.

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