Peptides are short chains of amino acids linked by peptide bonds. Most peptides contain from two to about fifty amino acids, while longer chains are typically classified as proteins. Because of their size, peptides can adopt simple shapes or remain largely unstructured, which influences how they interact with other molecules. Some peptides act as hormones or signaling molecules, while others are fragments derived from larger proteins. In the body, peptides can be produced directly as functional units or generated through proteolytic processing of bigger polypeptides. When a peptide encounters a specific receptor, it can bind and trigger a signaling cascade inside the cell. Receptors may reside on the cell surface or within the cell, and binding can activate second messengers such as cyclic AMP or calcium signals. The exact cellular response depends on the peptide sequence, its structure, and the context of the cell. Peptides are rapidly degraded by peptidases, which cleave them into shorter fragments for disposal or reuse. The combination of selective recognition and controlled turnover helps maintain precise signaling throughout the body. Peptides are central to many physiological processes because they act as messengers that coordinate activity across tissues. Their proper function supports the regulation of pathways involved in growth, metabolism, and homeostasis, among others. Disruptions to peptide signaling can alter cellular communication and downstream responses. Because of their modular nature, peptides can be studied as discrete units to understand how sequence and conformation influence interaction with receptors. In research, peptides are used to probe receptor binding, selectivity, and the dynamics of signaling networks. For researchers and students, peptides are accessible tools for exploring biology today. Techniques such as mass spectrometry and chromatography enable detection and quantification of specific peptides in complex samples. Antibody-based assays and affinity methods provide complementary readouts of peptide presence and function. Peptide synthesis, including solid-phase methods, allows the creation of custom sequences for study. Computational design and structural biology help predict how changes in sequence affect binding and activity, supporting a practical understanding of peptide behavior.
