8.2 Electron transport chain and oxidative phosphorylation
3 min read•august 7, 2024
The electron transport chain and are the final stages of . These processes harness energy from electrons to create a , ultimately producing , the cell's energy currency.
In this section, we'll explore the complexes involved in electron transport, key , and how the proton gradient drives . Understanding these processes is crucial for grasping how cells efficiently generate energy from nutrients.
Electron Transport Chain Complexes
Complex Structure and Function
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() oxidizes NADH, transferring electrons to and pumping protons across the inner mitochondrial membrane
(Succinate dehydrogenase) oxidizes succinate to fumarate, reducing ubiquinone and does not transport protons
(Cytochrome bc1 complex) transfers electrons from ubiquinol to , pumping protons across the inner mitochondrial membrane (Q cycle)
(Cytochrome c oxidase) transfers electrons from cytochrome c to oxygen, the final electron acceptor, pumping protons across the inner mitochondrial membrane
Electron Flow and Energy Release
Electrons flow through the complexes in order of increasing reduction potential, releasing energy at each step
Energy released from electron transfer is used to pump protons across the inner mitochondrial membrane, generating a proton gradient
Electron transport chain is the major site of ATP production in cellular respiration (oxidative phosphorylation)
Inhibitors of electron transport chain complexes (rotenone, antimycin A, ) can disrupt ATP production and lead to cell death
Electron Carriers
Coenzyme Q (Ubiquinone)
Lipid-soluble electron carrier that shuttles electrons between Complex I, II, and III
Exists in oxidized form (ubiquinone) and reduced form (ubiquinol)
Accepts electrons from NADH (via Complex I) and (via Complex II), becoming reduced to ubiquinol
Donates electrons to Complex III, becoming oxidized back to ubiquinone
Cytochrome c
Water-soluble electron carrier that shuttles electrons from Complex III to Complex IV
Heme-containing protein that alternates between reduced (ferrous, Fe2+) and oxidized (ferric, Fe3+) states
Accepts electrons from Complex III (cytochrome c1) and donates them to Complex IV
Cytochrome c release from mitochondria can trigger apoptosis (programmed cell death)
Proton Gradient and Membrane
Proton Gradient Formation and Function
Proton gradient is formed by the pumping of protons (H+) from the mitochondrial matrix to the intermembrane space
Complexes I, III, and IV contribute to the proton gradient by coupling electron transfer to proton pumping
Proton gradient is used to drive ATP synthesis through ATP synthase (chemiosmotic coupling)
Proton gradient also powers other processes (mitochondrial protein import, metabolite transport)
Redox Reactions and Electron Transport
involve the transfer of electrons between molecules, with one molecule being oxidized (losing electrons) and the other reduced (gaining electrons)
Electron transport chain involves a series of redox reactions, with electrons being transferred from NADH and FADH2 to oxygen
Redox potential difference between electron donors (NADH, FADH2) and acceptors (ubiquinone, cytochrome c, oxygen) drives electron flow
Electron transport is coupled to proton pumping, converting redox energy into a proton gradient
Inner Mitochondrial Membrane Structure and Function
Inner mitochondrial membrane is highly folded, forming cristae that increase surface area for electron transport and ATP synthesis
Electron transport chain complexes and ATP synthase are embedded in the inner mitochondrial membrane
Inner mitochondrial membrane is impermeable to protons, allowing the formation and maintenance of the proton gradient
Cardiolipin, a unique phospholipid found in the inner mitochondrial membrane, is essential for the function of electron transport chain complexes and ATP synthase