Peptide hormones typically consist of anywhere from a few to several dozen amino acids-examples include insulin (51 amino acids) and antidiuretic hormone (9 amino acids). Their synthesis involves processes such as gene transcription and post-translational modifications (e.g., folding and cleavage); the mature peptides are ultimately stored in secretory granules and released in response to physiological signals.
Peptide hormones travel through the bloodstream to target organs, where they bind to G protein-coupled receptors or tyrosine kinase receptors on the cell surface, thereby triggering intracellular signaling pathways. For instance, insulin binding to its receptor activates glucose transporters, facilitating cellular glucose uptake, whereas growth hormone indirectly promotes bone growth by stimulating the liver to produce insulin-like growth factor 1 (IGF-1).
