Peptides

• Peptide


  Unbranched chain of covalently linked amino acids

  
• Types of peptides


  • Dipeptide (two amino acids)
  • Tripeptide (three amino acids)
  • Oligopeptide (10-20 amino acids)
  • Polypeptide (long unbranched chain of amino acids)

  
• Peptide formation


  1. Condensation of amino acids

  2. Amino group of one amino acid reacts with carboxyl group of another

  3. Releases H2O
• Amino acid residue


  Portion of an amino acid structure left after peptide formation
• Peptide bond


  Covalent bond between amino acids in a peptide chain, between carboxyl group of one and amino group of another

  
• Peptide bond


  • Planar structure
  • Partial double bond character, rigid and planar
  • Trans isomer is preferred orientation

  
• 1. terminal end


  End with free amino group
• 1. terminal end


  End with free carboxyl group
• Peptide nomenclature


  Start at N-terminal, C-terminal amino acid keeps full name, other residues end in -yl

  
• Isomeric peptides


  • Glu-Ser-Ala
  • Ser-Glu-Ala

  
• Oxytocin and Vasopressin


  Nonapeptides (9 amino acid residues) with disulfide bond forming a loop

  
• Oxytocin


  • Regulates uterine contractions and lactation
• Vasopressin


  • Regulates water excretion by kidneys, affects blood pressure
• Met-enkephalin and Leu-enkephalin


  Pentapeptide neurotransmitters that bind receptors in brain to reduce pain
• Glutathione (GSH)


  Tripeptide regulator of redox reactions, antioxidant
• Aspartame


  Dipeptide artificial sweetener (Asp-Phe)
• Amino acid sequence


  Order of amino acid residues in a peptide

  
• Difference in amino acid sequence

  Results in difference in physiological properties
• Bradykinin and Boguskinin


  • Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg (active)
  • Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe (inactive)
• Normal Hb sequence: Val-His-Leu-Thr-Pro-Glu-Glu-Lys-Ser-Ala
• Sickle-cell Hb sequence: Val-His-Leu-Thr-Pro-Val-Glu-Lys-Ser-Ala
• Georgetown anemia sequence: Val-His-Leu-Thr-Pro-Glu-Lys-Lys-Ser-Ala
• Drills: Write the structure of the following peptides

  1. Lys-Phe-Asp-Ala

  2. Val-His-Leu-Thr-Pro

  3. Val-Glu-Lys-Ser-Ala
• Peptide


  Unbranched chain of covalently linked amino acids

  
• Types of peptides

  • Dipeptide (two amino acids)
  • Tripeptide (three amino acids)
  • Oligopeptide (10-20 amino acids)
  • Polypeptide (long unbranched chain of amino acids)

  
• Peptide formation

  1. Condensation of amino acids

  2. Amino group of one amino acid reacts with carboxyl group of another

  3. Release of H2O

  
• Amino acid residue

  Portion of an amino acid structure left after peptide formation
• Peptide bond

  • Covalent bond between amino acids
  • Between carboxyl group of one amino acid and amino group of another

  
• 1. terminal end

  End with free amino group
• 1. terminal end

  End with free carboxyl group
• Peptide nomenclature

  Start at N-terminal, C-terminal amino acid keeps full name, other residues end in -yl

  
• Peptide names

  • Alanylprolylglutamylglycine

  
• Peptide bond structure

  • Planar, partial double bond character, hindered rotation, trans isomer preferred

  
• Isomeric peptides

  Peptides with same amino acids in different order

  
• Oxytocin and vasopressin are nonapeptides produced by the pituitary gland
• Oxytocin


  Regulates uterine contractions and lactation
• Vasopressin

  Regulates water excretion by kidneys, affects blood pressure
• Met-enkephalin and Leu-enkephalin

  Pentapeptide neurotransmitters produced by the brain that bind receptors to reduce pain
• Glutathione (GSH)


  Tripeptide regulator of redox reactions, antioxidant
• Aspartame

  Dipeptide artificial sweetener (180x sweeter than sucrose)