Extracellular Signaling Receptors

Abstract

Classically, receptors were defined as cellular structures that recognize and bind hormones. In present days this definition is expanded to include receptors for a variety of other extracellular regulatory signaling molecules, such as growth factors and neurotransmitters. Accordingly, the term ligand was introduced to encompass all the extracellular signaling molecules that bind to receptors. The main attribute of receptors is their ability to specifically recognize a ligand among the many different molecules present in the environment surrounding the cells. Ligand-specific binding results in activation of intracellular signaling pathways, which amplify the signal and affect gene expression. Thus, receptors not only receive extracellular signals but also increase and transmit those signals to the genome and ultimately elicit a biological response.