Chemiosmosis
Protons pumped across a membrane build a gradient, then flow back through ATP synthase, a molecular turbine that makes ATP. The gradient is called the proton-motive force.
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Analogy
A dam: water pumped up behind it spins a turbine as it flows back.
In practice
About 26 to 28 of the roughly 30 ATP from one glucose come from this step.
Practice
Flashcards
- What drives ATP synthase?Protons flowing back down their gradient across the inner mitochondrial membrane.
Interview questions
- Outline the stages of aerobic respiration and say where each occurs and what it produces.
- Glycolysis in cytoplasm: 2 ATP, 2 NADH
- Citric acid cycle in matrix: NADH, FADH2, CO2
- Electron transport and chemiosmosis in inner membrane: most ATP
- Oxygen is final electron acceptor
- Explain how a proton gradient makes ATP in mitochondria.
- Electron flow pumps protons into intermembrane space
- Gradient stores potential energy
- Protons flow through ATP synthase
- Flow drives ADP plus phosphate into ATP
Questions people ask
Where does the ATP synthase get its energy?
From the flow of protons down their gradient. The enzyme works like a turbine: protons passing through make part of it rotate, and the rotation changes the shape of binding sites so ADP and phosphate are pushed together to form ATP. About 3 or 4 protons are needed per ATP.
Can uncoupling the gradient be useful?
Yes. Brown fat cells in babies and hibernating animals contain a protein that lets protons leak back across the membrane without making ATP. The energy of the gradient is released as heat instead. This helps keep newborn mammals warm without shivering.