Peptide Glossary

The fundamental building blocks of peptides and proteins, consisting of an amine group, a carboxylic acid group, and a unique side chain.

The fraction of a dose that actually reaches the bloodstream and is available to work. Oral semaglutide has a bioavailability of just 0.4–1%, but it still works because the drug is extremely potent and very long-lasting.

A 15-amino-acid peptide first identified in human gastric juice, popular in wellness communities for purported tendon and gut healing. It currently sits on the FDA Category 2 list, meaning compounding pharmacies cannot legally produce it.

A growth-hormone-releasing hormone analog that prompts the pituitary gland to release growth hormone in natural pulses. Also on the FDA Category 2 list; risks include hormonal imbalance, joint pain, and metabolic disruption.

A list maintained by the FDA of substances that compounding pharmacies are barred from making. In 2023 the FDA placed 19 peptides — including BPC-157 and CJC-1295 — on Category 2, citing immunogenicity concerns and lack of human clinical data.

A drug that mimics glucagon-like peptide-1, a natural gut hormone that signals the pancreas to release insulin and tells the brain you are full.

The time it takes for the amount of a drug in the body to drop by half. Natural GLP-1 has a half-life under two minutes; semaglutide has been engineered to about a week.

The tendency of a drug to provoke an immune response. Synthetic peptides — especially modified ones — can be flagged as foreign, triggering anti-drug antibodies that range from a rash to anaphylaxis.

The broader family of drugs that imitate the gut hormones (incretins) the body releases in response to food. GLP-1 receptor agonists are the best-known example.

A covalent chemical bond formed between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water.

Chemical modifications made to a protein after its synthesis, such as phosphorylation, glycosylation, or proteolytic cleavage.

The linear sequence of amino acids in a peptide or protein chain.

The large-scale study of proteins, particularly their structures and functions within a biological system.

The structural organization of multiple polypeptide chains (subunits) into a single functional complex.

Local spatial arrangements of the polypeptide backbone, primarily alpha-helices and beta-sheets, stabilized by hydrogen bonds.

The first FDA-approved oral peptide permeation enhancer. SNAC briefly raises stomach pH, fluidizes the gastric membrane, and lets a peptide cross into the bloodstream — making oral semaglutide possible.

R. Bruce Merrifield's 1963 invention. The growing peptide is anchored to an insoluble resin so excess reagents can be rinsed away after each step, pushing reaction efficiency to roughly 99.5% and cutting timelines from years to days.

The overall three-dimensional shape of a single polypeptide chain, driven by hydrophobic interactions, disulfide bridges, and ionic bonds.