electron transport chain
Summary
The electron transport chain (ETC) is a series of protein complexes in the inner mitochondrial membrane that transfers electrons from NADH and FADH2 to oxygen, generating ATP through oxidative phosphorylation. This process produces approximately 32-34 ATP molecules per glucose molecule and is the final step of cellular respiration.
Detail
The electron transport chain consists of four main protein complexes (I-IV) embedded in the inner mitochondrial membrane. Complex I (NADH dehydrogenase) accepts electrons from NADH, while Complex II (succinate dehydrogenase) accepts electrons from FADH2. Electrons are passed sequentially through Complexes I→III→IV or II→III→IV, with coenzyme Q (ubiquinone) and cytochrome c serving as mobile electron carriers. As electrons move through the chain, protons are pumped from the mitochondrial matrix into the intermembrane space, creating an electrochemical gradient. This proton gradient drives ATP synthase (Complex V) to produce ATP from ADP + Pi. The final electron acceptor is oxygen, which combines with protons to form water. Disruption of the ETC (by cyanide, carbon monoxide, or rotenone) can be fatal as it halts ATP production. The ETC is also the primary site of reactive oxygen species (ROS) production, particularly at Complexes I and III.
Sources
- Lehninger Principles of Biochemistry
- First Aid for USMLE Step 1
- Lippincott's Illustrated Reviews: Biochemistry
- Kaplan USMLE Step 1 Biochemistry
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