110 likes | 330 Views
27.7 Peptides. Peptides. Peptides are compounds in which an amide bond links the amino group of one -amino acid and the carboxyl group of another. An amide bond of this type is often referred to as a peptide bond. H. H. O. O. +. +. –. –. O. O. H 3 N. H 3 N. C. C. C. C. CH 3.
E N D
Peptides • Peptides are compounds in which an amide bond links the amino group of one -amino acid and the carboxyl group of another. • An amide bond of this type is often referred to as a peptide bond.
H H O O + + – – O O H3N H3N C C C C CH3 H Alanine and Glycine
H H O O + – H3N N O C C C C CH3 H H Alanylglycine • Two -amino acids are joined by a peptide bond in alanylglycine. It is a dipeptide.
H H O O + – H3N N O C C C C CH3 H H Alanylglycine C-terminus N-terminus Ala—Gly AG
H H O O + – H3N N O C C C C CH3 H H H H O O + – H3N N O C C C C H H CH3 Alanylglycine and glycylalanine are constitutional isomers Alanylglycine Ala—Gly AG Glycylalanine Gly—Ala GA
H H O O + – H3N N O C C C C CH3 H H Alanylglycine • The peptide bond is characterized by a planar geometry.
Higher Peptides • Peptides are classified according to the number of amino acids linked together. • dipeptides, tripeptides, tetrapeptides, etc. • Leucine enkephalin is an example of a pentapeptide.
Leucine Enkephalin Tyr—Gly—Gly—Phe—LeuYGGFL
4 5 3 Ile—Gln—Asn 2 Tyr Cys—Pro—Leu—GlyNH2 6 7 8 9 1 Cys S S Oxytocin • Oxytocin is a cyclic nonapeptide. • Instead of having its amino acids linked in an extended chain, two cysteine residues are joined by an S—S bond. C-terminus N-terminus
Oxytocin S—S bond An S—S bond between two cysteines isoften referred to as a disulfide bridge.