Molecular Weight
The total mass of a molecule, calculated by summing the atomic weights of all its constituent atoms. For peptides, molecular weight is typically expressed in daltons (Da) or kilodaltons (kDa) and is a key identifying characteristic used in quality testing and regulatory classification.
Technical Context
Molecular weight is calculated by summing atomic weights of all constituent atoms and is measured in daltons (Da) or kilodaltons (kDa). Small peptides range from a few hundred Da (e.g. TRH at 362 Da) to several thousand. Larger therapeutic peptides approach or exceed protein range: somatropin is approximately 22,124 Da, insulin approximately 5,808 Da, and semaglutide approximately 4,114 Da. Molecular weight affects pharmacokinetic properties including renal filtration (molecules above approximately 60,000 Da are not efficiently filtered by the kidneys), cellular permeability, and analytical method selection. It also determines whether chemical synthesis or recombinant production is more appropriate.