What is a proton pump?
In: Biology
They’re a type of protein that’s embedded in the membrane surrounding cells that moves H+ (hydrogen ions, a hydrogen without an electron, aka a proton) from the inside of the cell to the external environment.
Since pH (how acidic something is) is a measure of how many H+ ions there are present, this makes the environment more acidic. So your stomach lining, for example, has a lot of proton pumps, and proton pump inhibitor drugs are used to reduce the amount of stomach acid produced.
Protons can’t pass through the cell membrane freely (it would actually be bad if they could, since our cells couldn’t regulate their pH, and more broadly, life as we know it just wouldn’t work), which is why they need assistance from proton pumps. The process uses up energy. (ATP)
Edit: And as u/Arcaeca2 wrote, they’re also used to make ATP in the mitochondria, but I’m really not up to trying to explain cellular respiration and the electron transport chain in an ELI5.
It’s a cellular mechanism that moves hydrogen atoms. It creates an energy gradient for storing energy for later, but it also makes one side more acidic. For example your stomach has proton pumps that make the water inside your stomach gradually more and more acidic so that you can digest food.
Chemicals in general move from areas of high concentration to low concentration. This is bad if you need a certain chemical to *always* be at a high concentration in a particular spot in order for something to work.
H+ ions, sometimes called “protons” because that’s all that’s left when you remove an electron from hydrogen*, are one such chemical that need to be constantly kept at high concentration in certain places. For example, your stomach, so your stomach fluid always stays acidic. Or inside** your mitochrondria, where they’re used to power ATP synthase to create ATP.
So, proteins exist that force H+ ions into areas that already have a ton of H+ ions, the opposite direction they *want* to go (*against* the high -> low concentration gradient), because unless you’re constantly forcing them to go there, they’ll eventually go somewhere else, and then things break. Proteins that move H+ against the gradient are called “proton pumps”.
(* This technically isn’t true, you can’t just have a single proton chilling on its own like that. Technically you’re transferring a proton between different water molecules, from an H3O+ molecule onto an H2O molecule, onto another H2O molecule, onto another H2O molecule, onto another H2O molecule, etc.)
(** Mitochondria technically have two different “layers” of “inside”. The place where H+ needs to accumulate is in the outermost inside, called the “intermembrane space”.)
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