electron transport chain

Definition

Target type: biologicalprocess

A process in which a series of electron carriers operate together to transfer electrons from donors to any of several different terminal electron acceptors. [GOC:mtg_electron_transport]

The electron transport chain (ETC) is a series of protein complexes embedded within the inner mitochondrial membrane, playing a crucial role in cellular respiration. This process converts chemical energy from food into a usable form, ATP, which is the cell's primary energy currency.

The ETC harnesses the energy released from the oxidation of electron carriers, NADH and FADH2, generated during the citric acid cycle. These carriers deliver electrons to the ETC, initiating a cascade of redox reactions that ultimately transfer electrons to molecular oxygen. This process involves four major protein complexes:

1. **Complex I (NADH dehydrogenase):** Accepts electrons from NADH and transfers them to ubiquinone (Q), a small lipid-soluble molecule that acts as an electron carrier within the membrane. This process pumps protons from the mitochondrial matrix to the intermembrane space, contributing to the proton gradient.

2. **Complex II (Succinate dehydrogenase):** This complex receives electrons from FADH2, which is generated during the citric acid cycle. Unlike Complex I, Complex II does not directly contribute to the proton gradient.

3. **Complex III (Ubiquinone-cytochrome c reductase):** Accepts electrons from ubiquinol (QH2), the reduced form of ubiquinone, and transfers them to cytochrome c, another mobile electron carrier. This process also contributes to the proton gradient by pumping protons from the matrix to the intermembrane space.

4. **Complex IV (Cytochrome c oxidase):** Receives electrons from cytochrome c and finally transfers them to molecular oxygen, reducing it to water. This process is the terminal step in the ETC and is coupled to the pumping of protons across the membrane, further increasing the proton gradient.

The proton gradient established across the inner mitochondrial membrane drives the synthesis of ATP by ATP synthase. This enzyme utilizes the energy stored in the proton gradient to phosphorylate ADP into ATP, a process known as oxidative phosphorylation.

In summary, the ETC involves a series of redox reactions that transfer electrons from NADH and FADH2 to molecular oxygen, generating a proton gradient across the inner mitochondrial membrane. This gradient is then harnessed by ATP synthase to produce ATP, the cell's primary energy source.'
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Proteins (1)

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