What is the Origin of Secondary Messenger System?

This concept is foundational to molecular endocrinology and cell biology, developed to explain the mechanism of action for non-steroid hormones. The term 'secondary messenger' was coined to distinguish these intracellular molecules from the 'first messenger,' which is the hormone itself. The discovery of cyclic AMP (cAMP) as a key relay molecule was a landmark achievement in understanding cellular signal transduction.

What is the Mechanism of Secondary Messenger System?

The process begins with the hormone binding to a G-protein coupled receptor (GPCR) on the cell membrane, which activates the associated G-protein. This activation then triggers the synthesis or release of the secondary messenger molecules, such as cAMP, inositol triphosphate (IP3), or calcium ions. These messengers rapidly diffuse through the cytoplasm, activating a series of downstream protein kinases, such as Protein Kinase A, which ultimately phosphorylate target proteins to alter the cell's metabolic state or genetic transcription.

Secondary Messenger System ∞ Area

Secondary Messenger System

Meaning

The Secondary Messenger System is a cascade of intracellular molecules that functions to relay and amplify the signal initiated when a water-soluble hormone, or first messenger, binds to a receptor on the cell surface. Since these hormones cannot cross the lipid membrane, this system is essential for transducing the external signal into a specific internal physiological response, such as enzyme activation or gene expression modulation. This mechanism allows for a highly regulated and rapid cellular response to endocrine cues.