Redox Potentials and the Proton-Motive Force
Electrons pass down a chain of carriers arranged in order of their standard potentials, and the energy released at three points is used to move protons out. The gradient stores that energy as both a concentration difference and a voltage.
What a learner can do afterwards
- Orders carriers by potential and calculates the energy available for a stated electron transfer.
- Separates the two components of the proton-motive force and says which dominates in mitochondria.
- Predicts what an uncoupler does to electron flow and to ATP production.
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The electron transport chain passes electrons down carriers ordered by increasing reduction potential, from NADH through complexes to oxygen. Each downhill transfer releases energy that pumps protons across the inner mitochondrial membrane, and the resulting gradient stores energy as the proton-motive force. Oxygen sits at the bottom as the final acceptor, which is why respiration stops without it.
You can price any step with the Faraday constant, 96.5 kJ per volt per mole. Moving 2 electrons across 0.2 volts releases 2 times 96.5 times 0.2, which is 38.6 kJ per mole. A bigger potential drop buys more pumping energy, which is why carrier order sets the energy budget of the chain.
The proton-motive force has two components: a pH difference and a membrane voltage, and in mitochondria the voltage dominates. Pumped protons gather in the intermembrane space, leaving the matrix negative and alkaline, and both components push protons back inward through ATP synthase. Uncouplers let protons leak back past the synthase, so electron flow speeds up while ATP production collapses, which proves the gradient is the true intermediate.
Check direction first in every question: electrons fall from low to high potential and end at oxygen. Redox bookkeeping stays simple if you remember that the donor is oxidized, the acceptor is reduced, and NADH becomes NAD plus when it donates.
Electrons fall down ordered carriers toward oxygen, and the released energy is stored as a proton gradient with voltage and pH parts.
More to read
7.4 Oxidative Phosphorylation
The electron transport chain passes electrons down a series of carriers ordered by increasing reduction potential, from NADH through complexes to oxygen. Each downhill transfer releases energy that pumps protons across the inner mitochondrial membrane. The resulting gradient stores energy as the proton motive force. Oxygen sits at the bottom as the final acceptor, which is why respiration stops without it.
Oxidative Phosphorylation: The major energy provider of the cell
This review connects electron flow to ATP production through the gradient. It explains how complexes move protons as electrons fall in potential, and how ATP synthase harvests the gradient to make ATP. Uncouplers get special attention: they let protons leak back without passing through the synthase, so electron flow speeds up while ATP production collapses. That split proves the gradient is the true intermediate.
5.2 Passive Transport
Ions move down electrochemical gradients, which combine a concentration difference with an electrical voltage difference. The proton motive force has exactly these two components: a pH difference and a membrane voltage. In mitochondria the voltage component dominates, with the matrix negative relative to the intermembrane space. Both components push protons back inward through ATP synthase.
Learn: Introduction to cellular respiration and redox
Redox reactions move electrons from a donor to an acceptor, and the donor is oxidized while the acceptor is reduced. NADH carries high energy electrons from fuel to the chain, becoming NAD plus in the process. Oil rig, oxidation is loss and reduction is gain, keeps the bookkeeping straight. Every ATP made downstream traces back to one of these electron donations.
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Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.