Question

In the mitochondria of human cells, energy for the production of ATP is provided by the oxidation and reduction reactions of the iron ions in the cytochromes in electron transport. Identify each of the following reactions as an oxidation or reduction: a. \(\mathrm{Fe}^{3+}+e^{-} \longrightarrow \mathrm{Fe}^{2+}\) b. \(\mathrm{Fe}^{2+} \longrightarrow \mathrm{Fe}^{3+}+e^{-}\)

Short answer

a. Reduction, b. Oxidation

Step-by-step solution

Define Oxidation and Reduction

Oxidation is the loss of electrons, while reduction is the gain of electrons. Use this to identify the reactions.

Analyze Reaction (a)

For reaction (a) \( \text{Fe}^{3+}+e^{-} \longrightarrow \text{Fe}^{2+} \), the reactant \( \text{Fe}^{3+} \) gains an electron \( (e^{-}) \) to become \( \text{Fe}^{2+} \). Hence, this reaction is a reduction.

Analyze Reaction (b)

For reaction (b) \( \text{Fe}^{2+} \longrightarrow \text{Fe}^{3+}+e^{-} \), the reactant \( \text{Fe}^{2+} \) loses an electron \( (e^{-}) \) to become \( \text{Fe}^{3+} \). Hence, this reaction is an oxidation.

Key concepts

Electron Transport in Mitochondria

Electron transport is a vital process in the mitochondria, the powerhouse of the cell. During electron transport, electrons are transferred through a series of protein complexes located in the inner mitochondrial membrane. This process creates a gradient of protons that leads to ATP production. When electrons move from one complex to another, they're transferred from molecules that lose them (oxidized) to those that gain them (reduced). This series of reactions is crucial for cellular respiration and energy production.

ATP Production

ATP (adenosine triphosphate) is the energy currency of the cell. It is produced during cellular respiration, mainly in mitochondria. The process of creating ATP involves harnessing the energy released from oxidation-reduction reactions occurring in the electron transport chain. This energy powers ATP synthase, an enzyme that synthesizes ATP from ADP (adenosine diphosphate) and an inorganic phosphate. The efficient production of ATP is essential for all cellular functions, from muscle contraction to metabolic processes.

Mitochondria - The Powerhouse of the Cell

Mitochondria are known as the powerhouse of the cell due to their role in energy production. They have a unique double-membrane structure, with the inner membrane folding into cristae to increase surface area. This is where the electron transport chain is located. The matrix, the innermost area of the mitochondrion, contains enzymes necessary for the citric acid cycle (Krebs cycle). Mitochondria also have their DNA, which is inherited maternally and is crucial in encoding proteins essential for the organelle's function.

Role of Cytochromes in Electron Transport

Cytochromes are a group of heme-containing proteins found within the inner mitochondrial membrane. They play a significant role in the electron transport chain by facilitating the transfer of electrons between different complexes. Each cytochrome has an iron ion that can alternate between two oxidation states: Fe3+ (oxidized) and Fe2+ (reduced). By accepting and donating electrons, cytochromes contribute to the creation of the proton gradient essential for ATP synthesis.

Importance of Iron Ions in Redox Reactions

Iron ions are central to the redox (reduction-oxidation) reactions occurring in the electron transport chain. Iron can exist in two different oxidation states, Fe3+ and Fe2+. During the transfer of electrons, iron ions in the cytochromes either gain an electron (reduction, Fe3+ to Fe2+) or lose an electron (oxidation, Fe2+ to Fe3+). These changes are vital for the continuous flow of electrons, ultimately facilitating the process of oxidative phosphorylation and efficient ATP production.