Pharmacology
Ligand
A ligand is a molecule that binds to a specific receptor or protein, initiating or modulating a biological response.
Detailed Explanation
Ligands can be endogenous (naturally occurring, like hormones and neurotransmitters) or exogenous (synthetic, like research peptides). The binding of a ligand to its receptor is governed by affinity (strength of binding) and specificity (selectivity for one receptor over others). Peptide ligands often have high specificity for their target receptors.