Amino acid residues dipepgde 2 tripepgdes 3

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Unformatted text preview: 20 amino acids in proteins •  differ by nature of R group, side chain α ­amino group α ­carboxyl group Amino Acids form PepGde Bonds •  CondensaGon reacGon amide linkage (pep+de bond) polymer Amino Acids vs. Amino Acid Residues •  DipepGde (2), tripepGdes (3), oligopepGde (short), polypepGde (long) •  Amino acid residue – amino acid within pepGde N ­terminus C ­terminus Amino Acids: ClassificaGon •  Common amino acids can be placed in five basic groups depending on their R subsGtuents: –  other textbooks may categorize in different way •  •  •  •  •  Nonpolar, aliphaGc (7) AromaGc (3) Polar, uncharged (5) PosiGvely charged (3) NegaGvely charged (2) ring rigid more carbons, more hydrophobic Absorbance Spectra of AromaGc Amino Acids •  Tryptophan and tyrosine absorb ultraviolet light –  (also phenylalanine but weaker) •  Used to characterize proteins thiol disulfide bond not very polar Disulfide Bond FormaGon •  The oxidaGon of two cysteines Disulfide bond •  Stabilizes the structures of many proteins Both neutral and protonated forms present at physiological pH conjugate bases of Aspar+c Acid, Glutamic Acid What kinds of weak interacGons do...
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