Body and drug basics
Protein
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A protein is a chain of amino acids too, just a long one. This site draws the line at about fifty amino acids: shorter is filed as a peptide, longer is treated as a protein. Long chains usually fold into a specific three-dimensional shape and do structural or chemical work, while short chains more often act as signals.
Why it matters here
The type on a compound record depends on this boundary, so it decides which shelf a compound sits on and which comparisons make sense. It also explains why a few familiar substances turn up under a type you might not have expected.
What it is not
The fifty-amino-acid line is arbitrary rather than chemical. Different references put it at forty, fifty or a hundred, and nothing about a molecule changes as it crosses. Insulin at fifty-one amino acids is a protein by that rule and is still universally called a peptide hormone, and that disagreement is genuine rather than an error on the page.
Also called
- protein
- proteins
- protein vs peptide
- peptide vs protein
- polypeptide
Polypeptide gets used for both long peptides and small proteins, which is part of why the boundary reads as blurry.
Compounds carrying this term
None on file yet. This term is in the controlled vocabulary but no compound record currently uses it — which is a statement about our coverage, not about the term.