Final answer:
The transition of heme iron between Fe3+ and Fe2+ oxidation states in the electron transport chain is facilitated by electron carriers such as cytochrome c, flavin mononucleotide, and coenzyme Q, contributing to the generation of ATP through oxidative phosphorylation.
Step-by-step explanation:
Electron Transport Chain and Heme Iron
In the electron transport chain (ETC), cytochrome c (Cyt c) and other electron carriers such as flavin mononucleotide (FMN), iron-sulfur clusters, and coenzyme Q (ubiquinone) assist in the transition of iron atoms in the heme group between the Fe3+ and Fe2+ oxidation states. The iron atom in the heme group of cytochrome c can accept and donate a single electron, transitioning between these oxidation states as it moves electrons between complex III and complex IV in the ETC. Cytochrome c is water-soluble and shuttles electrons in the intermembrane space of the mitochondria, while FMN accepts electrons from NADH in complex I and passes them to iron-sulfur clusters. Ultimately, electrons are transferred to coenzyme Q, which also participates in electron shuttling but within the hydrophobic environment of the mitochondrial inner membrane.
Complex III, known as cytochrome oxidoreductase, includes cytochrome b, iron-sulfur protein, the Rieske center, and cytochrome c1. This complex not only transfers electrons to cytochrome c but also pumps protons across the mitochondrial membrane, contributing to the generation of ATP through oxidative phosphorylation. The final electron acceptor in the ETC is oxygen, which combines with electrons and protons to form water, a process that takes place in complex IV.