peptidi

Peptidi, or peptides in English, are short chains of amino acids linked by covalent peptide bonds. They are the building blocks that lie between individual amino acids and larger proteins. Most definitions place peptides in the range from two to a few dozen amino acids, with longer chains sometimes called polypeptides or proteins depending on length and structure. Peptidi arise in biology through ribosomal synthesis or nonribosomal pathways and can be modified after assembly.

Each peptide has an N-terminus and a C-terminus; peptide bonds have partial double-bond character and planarity that restricts rotation. The primary structure is the sequence of amino acids; higher-order structures are limited in short peptides but can form motifs and secondary structures like turns, helices in longer ones.

Classification: dipeptides, tripeptides, oligopeptides (up to about 20-30 aa), polypeptides when longer. Ribosomal peptides are produced directly by ribosomes; nonribosomal peptides are assembled by multi-enzyme complexes. Some peptides are cyclic through disulfide bonds or head-to-tail cyclization; post-translational modifications such as phosphorylation or glycosylation alter function.

Biological roles: signaling molecules and hormones (insulin, glucagon, oxytocin, vasopressin), neurotransmitters and neuromodulators (endorphins), and antimicrobial peptides in innate immunity. They can act by binding to receptors or enzymes, or as proteolytic fragments with specific activities.

Synthesis and analysis: chemical synthesis using solid-phase peptide synthesis enables rapid production of defined sequences. Analytical methods include mass spectrometry and Edman degradation (historical) for sequencing. Peptide libraries and high-throughput approaches advance research.

Applications: therapeutics as peptide drugs with high specificity and safety profiles, diagnostic tools, cosmetic and biomaterials uses, and research reagents. Notable examples include insulin, oxytocin, vasopressin analogs, and therapeutic peptides such as pegylated peptides.