Structures of Amino Acids TABLE19.1 The 20 Common Amino Acids in Proteins pKa pKa pKa side Name Abbreviations MW Stucture a-CO2H a-NH3+ chain pl Neutral Amino Acids 0 Alanine Ala A 89 H3C、 2.34 9.69 6.01 0 H3N H O Asparagine Asn N 132 H2N 2.02 8.80 5.41 O H3N 0 Cysteine Cys C 121 1.96 10.28 8.18 5.07 HS 0 Glutamine Gln Q 146 2.17 9.13 5.65 H2N Glycine Gly G 75 2.34 9.60 5.97 0 Structures of Amino Acids