Receptors and Transmembrane Signaling

Receptors were recognized as a cell-surface phenomenon long before they were recognized as protein molecules located in a membrane. This phenomenon was the ability of an organism or cell to recognize a specific stimulus from the outside environment and to use the information to initiate a signal transduction pathway, producing changes in the organism's behavior or metabolism that usually improve the organism's chances for survival or affect a cell's interactions with its immediate environment. An increased understanding of receptors led to the generalization that receptors are in fact protein molecules which could process information from outside a cell to specific signal transduction pathways within the cell. The crucial link in that process is the ability of a protein molecule to be influenced by a stimulus—a chemical, light, mechanical compression, or even heat—and to deliver that information across the membrane to the inside of the cell, where the signal is amplified...