Chemiosmosis
MCAT glossary · Biological & Biochemical Foundations of Living Systems
Definition
The use of a proton gradient across a membrane to drive ATP synthesis via ATP synthase.
Chemiosmosis in plain English
Chemiosmosis is how cells actually turn stored energy into ATP, their usable fuel. The cell pumps positively charged particles called protons to one side of a membrane, building up a crowded, high-pressure zone — like water piling up behind a dam. Those protons desperately want to flow back to the less-crowded side, and the only door they can use is a spinning protein called ATP synthase. As the protons rush through and spin it like a turbine, that motion snaps together ATP molecules — the same basic idea as a hydroelectric dam turning falling water into electricity.
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