integral and peripheral proteins
/ IN-tuh-grul and puh-RIF-er-ul PROH-teenz /
Not every membrane protein sits in the membrane the same way. Some are bolted deep into the fatty wall like a window frame built right into a house; others just rest on the surface like a magnet stuck to a fridge door. These two styles are called integral proteins (the ones embedded in the membrane) and peripheral proteins (the ones loosely attached to its surface).
An integral protein has a part of itself that loves the oily middle of the bilayer, so it stays firmly wedged in the membrane and is hard to pull out without destroying the membrane. Many integral proteins, called transmembrane proteins, go all the way through, poking out on both sides — exactly what a transport channel or a signal receptor needs to do, since it must touch both the inside and the outside. A peripheral protein, by contrast, has no oily anchor; it clings to the watery surface of the membrane or to the tails of integral proteins, and can be coaxed off fairly gently.
The difference is practical, not just descriptive. Integral proteins do the heavy structural jobs of channels, pumps, and receptors. Peripheral proteins tend to be helpers: they relay signals just inside the cell, link the membrane to the cell's internal scaffolding, or assist enzymes. Knowing which type a protein is tells biologists how it behaves and how gently or harshly you must treat the membrane to study it.
A transmembrane channel that lets salt cross is integral — it pierces the whole wall. A signaling helper that only touches the inner surface, ready to carry a message deeper into the cell, is peripheral.
Integral = built into the wall; peripheral = stuck on the surface.
The terms describe how tightly a protein is held, not what it does — both types include important helpers; do not assume integral always means a transport channel.