Glossary
sodium-potassium pump
The sodium-potassium pump is a membrane protein that spends ATP to push three sodium ions out and pull two potassium ions in.
The sodium-potassium pump is a protein in the cell membrane that moves sodium and potassium against their gradients, and it is the reason a cell can hold a composition different from the fluid around it. For each molecule of ATP it splits, it carries three sodium ions out of the cell and two potassium ions in. That ratio is the point: three positive charges leave and only two arrive, so the inside of the cell ends up negative relative to the outside. Every cell of the body runs this pump, and nerve and muscle cells run it hardest, because the gradient it maintains is the stored charge a nerve impulse releases. It also keeps the cell from swelling, since by exporting more particles than it imports it offsets the water that would otherwise follow the solutes inward. A pump that stops — because the cell runs out of ATP — lets sodium leak in, water follow it, and the cell swell.
Taught in
Related terms
- osmosis — Osmosis is the movement of water across a selectively permeable membrane toward the side with more dissolved material, and it needs no energy.
- selectively permeable — A selectively permeable membrane lets some substances cross freely while blocking others, which is what makes a cell a separate compartment.
- ATP — ATP is the molecule cells use to carry energy — breaking off its third phosphate releases the energy a reaction needs.
Source: The biology guide in this course: its genetics definitions follow the National Human Genome Research Institute's Talking Glossary of Genomic and Genetic Terms, and its process descriptions follow the US National Cancer Institute's SEER Training Modules. Both are US federal government material, not subject to copyright in the United States. The microbiology entries — the bacterial cell, the Gram stain and the chain of infection — were written for this course from the infection-control guidance the biology guide's own source list names (US Centers for Disease Control and Prevention), which the genetics glossary does not cover. The definitions above are written for this course in our own words. (NHGRI Talking Glossary accessed 2026-10-26; definitions written 2026-10-27; the CDC basis for the microbiology entries — Principles of Epidemiology in Public Health Practice, third edition — accessed 2026-10-28, the date the biology guide's own source list records)