Short chains of amino acids, typically comprising 2 to 50 residues, that act as crucial intercellular messengers, regulating a vast array of physiological processes. These molecules function by binding to specific receptors on the surface of target cells, initiating a cascade of intracellular events that modulate hormone secretion, tissue repair, immune response, and neurological function. Unlike steroid hormones, they do not typically cross the cell membrane. The precise and potent action of peptide signaling molecules makes them an area of significant clinical interest for targeted therapeutic interventions.
Origin
The term combines “peptide,” derived from the Greek peptos meaning “digested” or “cooked,” referring to the small protein fragments, and “signaling molecules,” which is a descriptive term for any chemical messenger. Peptides were recognized as hormones, such as insulin, early in endocrinology, with a modern expansion into the broader category of signaling.
Mechanism
The mechanism of action is receptor-mediated: the peptide binds with high specificity to a transmembrane receptor on the target cell surface. This binding event induces a conformational change in the receptor, which then activates secondary messenger systems inside the cell, such as G-proteins or tyrosine kinases. This amplification cascade translates the external peptide signal into a specific, regulated cellular response, which can include changes in gene expression, enzyme activity, or cellular proliferation.
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