Electron transport chain
Series of redox reactions driving ATP synthesis via proton gradients.
An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions, coupling this electron transfer with the transfer of protons across a membrane. This process creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate (ATP), the primary energy currency of cells. The electron transport chain is fundamental to cellular respiration and photosynthesis, occurring in mitochondria, thylakoid membranes, and bacterial membranes.
- field
- Biochemistry, cellular respiration, photosynthesis
- known_for
- Coupling electron transfer to proton pumping and ATP synthesis via oxidative phosphorylation
- location
- Inner mitochondrial membrane (eukaryotes), thylakoid membrane (photosynthetic eukaryotes), bacterial membranes
Lore & Background
The electron transport chain comprises an enzymatic series of electron donors and acceptors embedded in membranes. In mitochondria, electrons from NADH and FADH2 pass through complexes I, II, III, and IV, with oxygen as the terminal electron acceptor, producing water. Each reaction releases energy because a higher-energy donor and acceptor convert to lower-energy products, and this energy is used to pump protons across the membrane, generating an electrochemical gradient.
Reader's Guide
The electron transport chain is significant because it is the primary mechanism for ATP production in aerobic respiration, converting the energy from redox reactions into a usable form. The proton gradient created by the chain powers ATP synthase, which phosphorylates ADP to ATP. In anaerobic respiration, alternative electron acceptors such as sulfate are used. The chain also plays a role in photosynthesis, where light energy drives electron transport and proton pumping. Its components, including complexes I–IV and mobile carriers like ubiquinone and cytochrome c, are highly conserved and essential for cellular energy metabolism.
Did You Know?
- Complex I is one of the main sites of premature electron leakage to oxygen, producing superoxide.
- In Complex II, no protons are transported to the intermembrane space, so it contributes less energy to the overall process.
- The Q-cycle in Complex III contributes to the proton gradient by asymmetric absorption and release of protons.
- In photosynthetic eukaryotes, the electron transport chain is found on the thylakoid membrane, where light energy drives electron transport.
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