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Douglas Harper's Etymology Dictionary

1906, from German peptid; see peptone + -ide, probably indicating a derivative.


n. 1 (context biochemistry English) A class of organic compounds consisting of various numbers of amino acids in which the amine of one is reacted with the carboxylic acid of the next to form an amide bond. 2 (context biochemistry English) The peptide bond itself.


n. amide combining the amino group of one amino acid with the carboxyl group of another; usually obtained by partial hydrolysis of protein


Peptides (from Gr.: πεπτός, peptós "digested"; derived from πέσσειν, péssein "to digest") are biologically occurring short chains of amino acid monomers linked by peptide ( amide) bonds.

The covalent chemical bonds are formed when the carboxyl group of one amino acid reacts with the amine group of another. The shortest peptides are dipeptides, consisting of 2 amino acids joined by a single peptide bond, followed by tripeptides, tetrapeptides, etc. A polypeptide is a long, continuous, and unbranched peptide chain. Hence, peptides fall under the broad chemical classes of biological oligomers and polymers, alongside nucleic acids, oligosaccharides and polysaccharides, etc.

Peptides are distinguished from proteins on the basis of size, and as an arbitrary benchmark can be understood to contain approximately 50 or fewer amino acids. Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to ligands such as coenzymes and cofactors, or to another protein or other macromolecule ( DNA, RNA, etc.), or to complex macromolecular assemblies. Finally, while aspects of the lab techniques applied to peptides versus polypeptides and proteins differ (e.g., the specifics of electrophoresis, chromatography, etc.), the size boundaries that distinguish peptides from polypeptides and proteins are not absolute: long peptides such as amyloid beta have been referred to as proteins, and smaller proteins like insulin have been considered peptides.

Amino acids that have been incorporated into peptides are termed "residues" due to the release of either a hydrogen ion from the amine end or a hydroxyl ion from the carboxyl end, or both, as a water molecule is released during formation of each amide bond. All peptides except cyclic peptides have an N-terminal and C-terminal residue at the end of the peptide (as shown for the tetrapeptide in the image).

Usage examples of "peptide".

Oh yes, it is an interesting accomplishment, but beyond it we are facing a damned blank wall which we do not have techniques to penetrate, may not have for many years, and even then the peptide Peat-Smith has postulated may not be behind the wall.

What was known, via a letter from Nigel Bentley, the Harlow administrator, was that the British technical achievement involved purification of a brain peptide mixture obtained from rats, and maze tests on rats had shown it to be effective in improving the memories of older animals.

Despite favorable signals, the latest peptide mix presented difficulties.

For the work of further refining, and to identify and isolate the single, critical memory peptide, larger quantities were essential.

That alone was excellent news but, to top it, there had been a successful refinement of the peptide mix, eventually allowing isolation of a single active peptide.

This-the much-sought-after Peptide-proved to be the seventh band on the original chromatogram films and was immediately referred to as Peptide 7.

It concerned the older rats that had been receiving regular peptide injections over several months.

Could it be that Peptide 7, while beneficial to the mind, was harmful to the body?

They were a group which, for several months, had been injected with the partially purified peptide mix, and more recently with peptide 7.

Suppose Peptide 7, as well as improving memory, caused a healthy weight loss.

At the same time, tests for Peptide Ts safety and effectiveness continued via injections into animals.

And titillating the public now could help sales of Peptide 7 later on.

Celia was shocked to learn of the Harlow devastation-so much in contrast to the recent heady progress reports concerning Peptide 7.

Even now she was thinking, with excited optimism, about Peptide 7 and Hexin W.

Now, not only was all of it recovered, but development of Peptide 7 had advanced to the point of being ready for a management product review.