Amino Acids. Amino Acid Structure Basic Structure: – (α) Carbon – Carboxylic Acid...
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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)
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
Prentice Hall c2002Chapter 3*Fig 3.7 Ionization of Histidine (a) Titration curve of histidine pK1 = 1.8 pK2 = 6.0 pK3 = 9.3
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