Chapter 23, Problem 23.94EP

Interpretation Introduction

Interpretation: To identify the electron carrier that shuttles electrons between protein complexes II and III.

Concept introduction: Electron transport chain is a sequence of biochemical reactions in which electrons and hydrogen atoms from the citric acid cycle are transferred to various intermediate carriers and finally reacts with molecular oxygen to form a water molecule. The reaction of the formation of the water is:

${\text{O}}_2+4{\text{e}}^{-}+4{\text{H}}^{+}\to 2{\text{H}}_{\text{2}}\text{O}$

There are four complexes associated with the electron transport chain that is present in the inner mitochondrial membrane. The four complexes that help in the electron transfer in the electron transport chain are:

Complex I: $\text{NADH-coenzyme}\text{Q reductase}$

Complex II: $\text{Succinate-coenzyme}\text{Q reductase}$

Complex III: $\text{Coenzyme}\text{Q-cytochrome c reductase}$

Complex IV: $\text{Cytochrome c oxidase}$

Mobile electron carriers are species that transfers electrons between the various complexes of the electron transport chain but is not directly associated with any of the four complexes. Examples of mobile electron carriers include $\text{coenzyme}\text{Q}$ and $\text{cytochrome c}$.