peptide (redirected from Polypeptide chain)

peptide, organic compound composed of amino acids linked together chemically by peptide bonds. The peptide bond always involves a single covalent link between the α-carboxyl (oxygen-bearing carbon) of one amino acid and the amino nitrogen of a second amino acid. In the formation of a peptide bond from two amino acids, a molecule of water is eliminated. Small peptides with fewer than about ten constituent amino acids are called oligopeptides, and peptides with more than ten amino acids are termed polypeptides. Compounds with molecular weights of more than 10,000 (50–100 amino acids) are usually termed proteins. Organisms commonly contain appreciable quantities of low-molecular-weight peptides some arising from proteins while others are synthesized directly. Certain of these molecules are unusual in that they incorporate amino acids not found in proteins such as amino acids of the d-configuration. Among the biological peptides are many with physiological or antibacterial activity, such as the peptide hormones oxytocin and vasopressin; adrenocorticotropic hormone (ACTH), secreted by the pituitary gland; and several cyclic peptides, in which the amino-acid sequence forms a ring structure rather than a straight chain, such as the antibiotics tyrocidin and gramicidin. Laboratory synthesis of peptides has risen to the level of a well-defined art in recent years. Synthetic peptides, composed of as many as a hundred amino acids in specified sequence, have been prepared in the laboratory with good purity and high yields.

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peptide

Organic compound composed of a series of amino acids linked by peptide bonds (see covalent bond) between a carbon atom of one and a nitrogen atom of the next. Peptide chains longer than a few dozen amino acids are called proteins. Biosynthesis of peptides from a succession of amino acids carried by transfer RNA molecules takes place on ribosomes and is catalyzed and controlled by enzymes. Many hormones, antibiotics, and other compounds that participate in life processes are peptides.

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peptide

any of a group of compounds consisting of two or more amino acids linked by chemical bonding between their respective carboxyl and amino groups

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peptide [′pep‚tīd]

(biochemistry)

A compound of two or more amino acids joined by peptide bonds.

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Peptide

A compound that is made up of two or more amino acids joined by covalent bonds which are formed by the elimination of a molecule of H₂O from the amino group of one amino acid and the carboxyl group of the next amino acid. Peptides larger than about 50 amino acid residues are usually classified as proteins. Glutathione is the most abundant peptide in mammalian tissue. Hormones such as oxytocin (8), vasopressin (8), glucagon (29), and adrenocorticotropic hormone (39) are peptides whose structures have been deduced; in parentheses are the numbers of amino acid residues for each peptide.

For each step in the biological synthesis of a peptide or protein there is a specific enzyme or enzyme complex that catalyzes each reaction in an ordered fashion along the biosynthetic route. However, it is noteworthy that, although the biological synthesis of proteins is directed by messenger RNA on cellular structures called ribosomes, the biological synthesis of peptides does not require either messenger RNA or ribosomes. See Amino acids, Protein, Ribonucleic acid (RNA), Ribosomes