Second Messenger Systems Activation is the rapid, intracellular cascade of molecular events triggered when a hormone or neurotransmitter binds to a specific receptor on the outer cell membrane. These crucial systems, such as cyclic AMP (cAMP) or calcium ions, translate the external signal into a specific, amplified internal cellular response. This mechanism is characteristic of peptide hormones and catecholamines, mediating fast, short-term physiological effects that regulate immediate cellular function.
Origin
This fundamental concept is a cornerstone of cell biology and pharmacology, originating with the discovery of cyclic AMP as the first second messenger by Earl Sutherland in the late 1950s, a Nobel Prize-winning breakthrough. The term ‘second messenger’ distinguishes these molecules from the ‘first messengers’ (the hormones or neurotransmitters) that bind to the cell surface. It elegantly explains how non-lipophilic signaling molecules can rapidly and powerfully influence cellular function without ever entering the nucleus.
Mechanism
The binding of the first messenger to its membrane receptor activates an associated G-protein, which then initiates the synthesis or release of the second messenger molecule within the cytoplasm. This second messenger rapidly diffuses to target specific enzymes or ion channels, leading to protein phosphorylation or changes in membrane potential. The final outcome is a swift and significant alteration in cellular activity, such as enzyme activation, rapid secretion, or muscle contraction.
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