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27.7 Peptides

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.

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27.7 Peptides

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  1. 27.7Peptides

  2. 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.

  3. H H O O + + – – O O H3N H3N C C C C CH3 H Alanine and Glycine

  4. 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.

  5. H H O O + – H3N N O C C C C CH3 H H Alanylglycine C-terminus N-terminus Ala—Gly AG

  6. 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

  7. H H O O + – H3N N O C C C C CH3 H H Alanylglycine • The peptide bond is characterized by a planar geometry.

  8. 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.

  9. Leucine Enkephalin Tyr—Gly—Gly—Phe—LeuYGGFL

  10. 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

  11. Oxytocin S—S bond An S—S bond between two cysteines isoften referred to as a disulfide bridge.

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