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Definition

noun, plural: extrinsic proteins

A membrane protein that partially span the membrane, and is attached either to the outer or to the inner phospholipid layer.

Supplement

Extrinsic proteins serve in transport of molecules and as receptors. They are held to the cell membrane by weak molecular attractions, like ionic, hydrogen, or Van der Waals bonds.

Word origin: LL extrinsecus, outward, adj. use of L extrinsecus (adv.) on the outward side.

Synonym: peripheral membrane protein.
Compare: intrinsic protein.
See also: cell membrane, fluid mosaic model.