Cell Signaling and Communication
Cell signaling is how cells sense and respond to their environment and to one another, converting extracellular signals into coordinated changes in cell behavior.
Definition
Cell signaling is the set of processes by which a cell detects an extracellular signal through receptors and transmits it through intracellular pathways to produce a specific response.
Scope
This area covers the general principles of signaling, the major classes of cell-surface receptors including G-protein-coupled receptors and receptor tyrosine kinases, the intracellular second messengers and cascades that relay signals, and how signaling networks integrate, amplify, and terminate information.
Sub-topics
Core questions
- How do cells convert an extracellular signal into an intracellular response?
- What distinguishes the major classes of cell-surface receptors?
- How do second messengers amplify and spread a signal inside the cell?
- How are signaling responses made specific, amplified, and then switched off?
Key theories
- Signal transduction through receptors and second messengers
- An extracellular ligand binding a receptor triggers an intracellular relay, often involving G proteins or kinases and diffusible second messengers, that amplifies and distributes the signal to effectors.
Mechanisms
A signaling molecule binds a specific receptor, changing its activity. Cell-surface receptors include G-protein-coupled receptors, which activate heterotrimeric G proteins, and receptor tyrosine kinases, which dimerize and autophosphorylate to recruit signaling proteins. Downstream, second messengers such as cyclic AMP, calcium ions, and lipid-derived molecules diffuse and activate kinases and other effectors, producing cascades that amplify the signal. Feedback, GTPase cycling, and phosphatases shape specificity and termination.
Clinical relevance
Signaling explains how cells coordinate growth, metabolism, movement, and gene expression, and provides the conceptual framework for understanding development and cellular regulation. The treatment here is descriptive and non-prescriptive.
History
Sutherland's discovery of cyclic AMP introduced the second-messenger concept; Rodbell and Gilman established G proteins as transducers between receptors and effectors, and Lefkowitz's work on receptor structure and regulation clarified how cell-surface receptors operate, building the modern map of signal transduction.
Key figures
- Alfred Gilman
- Martin Rodbell
- Earl Sutherland
- Robert Lefkowitz
Related topics
Seminal works
- gilman1987
- alberts2014
Frequently asked questions
- What is a second messenger?
- A second messenger is a small intracellular molecule, such as cyclic AMP or calcium, that is produced or released when a receptor is activated and that relays and amplifies the signal inside the cell.
- Why do signaling pathways amplify signals?
- Each active component can activate many downstream molecules, so a small number of bound receptors can trigger a large cellular response through a cascade of steps.