Chapter 25 - Membrane Receptors and Signal Transduction

Abstract

Cells specifically respond to a multiplicity of signals from their environment that cannot cross the plasma membrane. They achieve this via signal transduction cassettes, which comprise specific cell-surface membrane receptors, effector signaling systems, and regulatory proteins. These signal transduction cassettes serve to detect, amplify, and integrate diverse external signals to generate the appropriate cellular response. Binding of ligands to the extracellular face of membrane receptors stimulates transduction of signals through the membrane, coupling to different intracellular effector systems. Receptors can have intrinsic enzyme activity (e.g., protein kinase, protein phosphatase, ion-channel activity) or are coupled to proteins that stimulate the cytosolic generation of low-molecular-mass molecules, termed second messengers (e.g., cAMP, IP3, DAG, Ca2+). Second messengers subsequently stimulate intracellular signaling proteins, including phospholipases and protein kinases, that lead to the functional effect of the original signal. Tissue specificity of signaling is maintained by differential expression of receptors and effector proteins.