Amino acids and peptides
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Amino acids and peptides






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Amino acids and peptides Amino acids and peptides Presentation Transcript

  • Amino acids and peptides The “Lego” of proteins
  • Amino Acids • Same general structure • Called alpha amino acids • L- isomer is physiologically active • Side chain or R group determines other properties • Acid-base properties O H3N+ O R
  • Amino Acids, General • pK of carboxyl group around 2.3 – Deprotonated at physiological pH • R – COO- • pK of amino group around 9.5 – Protonated at physiological pH • H3N+-R • Some R-groups are acidic or basic
  • Nonpolar amino acids O NH3+ C H2 NH3+ H C O O H C H3C Leucine (L) O O CH3 CH3 Valine (V) O H + H N O H2C NH3+ CH3 Alanine (A) glycine(G) NH3+ O O CH3 NH3+ H3C O C H CH 2 H3C Isoleucine (I) Proline (P) O O
  • Aromatic Amino Acids O O H3N+ H3N+ O HO phenylalanine (F) pKr = 10.07 tyrosine (Y) O H3N+ O O N tryptophan (W)
  • Polar Amino Acids, alcohols O H3N+ HO Serine (S) O O H3N+ H3C O OH Threonine (T)
  • Polar Amino Acids (sulfur containing) O O H3N+ O N3N+ O HS Cysteine (C) H3C S Methionine (M)
  • Polar amino acids (amides) O H3N+ O O H3N+ O H2N O Asparagine (N) H2N O Glutamine (Q)
  • Charged Amino Acids (Acidic) O H3N+ O O H3N+ O O O Aspartate (D) pKr = 3.86 O O Glutamate (E) pKr = 4.25
  • Charged Amino Acids (Basic) O H3N+ O O H3N+ O O H3N+ HN N HN H2N NH2+ Arginie (R) pKr = 12.48 NH3+ Histidine (H) pKr = 6.0 Lysine (K) pKr = 10.53 O
  • Titration of Amino acids • Titration of glycine
  • Titration of Glutamate O pK = 9.67 H3N+ O pK = 2.19 O O Glutamate (E) pKr = 4.25
  • Purification of amino acids • Chromatography – Various types – Ion exchange • Uses net charge or can change with pH – Separate K, D and A – HPLC
  • Electrophoresis • Using electricity to move particles through a gelatinous matrix • Isoelectric point • IEF
  • Peptides • Peptide bond is amide linkage between amino acids • No free rotation about C-N bond due to partial double bond character of bond – resonance peptide bond H3N+ R1 - O O O O N H H3N+ R2 O + O N R1 R2
  • Tetrapeptide • Note planes of peptide bonds
  • Peptides • Peptides are vectorial – Have N and C termini • Sequences read H3N+---COOP-I-G O H2N+ O N H O N H O
  • Draw a tetrapeptide of L-A-R-D at physiological pH • Answer
  • Biologically Interesting Peptides • Aspartame – L-aspartyl-Lphenylalanine methyl ester O H3N+ O O N H O O CH3
  • Other small interesting peptides • Enkephalins Y-G-G-F-L Y-G-G-F-M • Oxytocin C-Y-I-Q-N-C-P-L-G-NH2 • Has C—C disulfide • Vasopressin C-Y-F-Q-N-C-P-R-G-NH2 • Also disulfide
  • Chemical Synthesis of Peptides • Why? • Done solid phase – Problem with in solution • Hard to make pure desired sequence – Purify by filtration • Side chains blocked • Made backwards ( C---N)
  • Scheme for peptide synthesis
  • Tetrapeptide answer A L O H3N+ O N H D R O N H O N H O O NH H2N+ • Back NH2 O