Amino Acids. Amino Acid Structure Basic Structure: – (α) Carbon – Carboxylic Acid...

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Transcript of Amino Acids. Amino Acid Structure Basic Structure: – (α) Carbon – Carboxylic Acid...

  • Amino Acids

  • Amino Acid StructureBasic Structure:() CarbonCarboxylic Acid GroupAmino GroupR-group Side ChainDetermines properties of Amino Acid R | H2N C COOH | H

    R Group Classification:- Non-polar, Polar, Aromatic, Acidic, and Basic

  • Non-Polar; HydrophobicGlycine (G)Alanine (A)Proline (P)Valine (V)Leucine (L)Isoleucine (I)Methionine (M)

  • Polar; HydrophilicSerine (S)Threonine (T)Cysteine (C)Asparagine (N)Glutamine (Q)

  • AromaticPhenylalanine (F)Hydrophobic

    Tyrosine (Y)Hydrophilic

    Tryptophan (W)Hydrophobic

  • Charged R-GroupsAcidic (positively-charged)Aspartate (D)Glutamate (E)

    Basic (negatively charged)Lysine (K)Arginine (R) - stronglyHistidine (H) - weakly

  • *The Peptide BondAmide bond formed by the COOH of an amino acid and the NH2 of the next amino acid O CH3 + | | + |NH3CH2COH + H3NCHCOO O CH3 + | | | NH3CH2C NCHCOO | peptide bond H

  • *PeptidesAmino acids linked by amide (peptide) bonds

    Gly Lys Phe Arg Ser

    H2N- -COOHendPeptide bonds end


  • Isoelectric PointEach amino acid has an isoelectric point, (pI) numerically equal to the pH at which the zwitterion concentration is at a maximum.The amino acid has no NET charge at its pI; it has one positive and one negative charge.At a pH less than the value of the isoelectric point, the amino acid is protonated and has a POSITIVE charge; at a pH greater than the pI the amino acid is deprotonated and has a NEGATIVE charge.CationNeutralAnion(zwitterion form)

  • Prentice Hall c2002Chapter 3*Fig 3.6 Titration curve for alanine Titration curves are used to determine pKa valuespK1 = 2.4 pK2 = 9.9 pIAla = isoelectric point

    Chapter 3

  • Prentice Hall c2002Chapter 3*Fig 3.7 Ionization of Histidine (a) Titration curve of histidine pK1 = 1.8 pK2 = 6.0 pK3 = 9.3

    Chapter 3

  • Derivatization with NinhydrinNinhydrin (2 mol) reacts with one mol of ANY amino acid to givethe SAME blue colored product. This reaction is performed post-column, after Ion Exchange Chromatography separation of a mixture of amino acids. The area of each peak in the chromatogram is proportional to the relative molar amount of the amino acid of that retention time.

  • Disulfide bonding in peptides[O]

  • Sangers Reagent: N-terminal Amino Acid Analysis

  • Sangers Reagent, contd

  • Carboxypeptidase: C-terminal AA Analysis

  • Prentice Hall c2002Chapter 3* Acid-catalyzed hydrolysis of a peptide

    Chapter 3