32. Ionic Forms of Alanine Alanine is a diprotic acid that can undergo two dissociation reactions (see Table 3-1 for pKa values). (a) Given the structure of the partially protonated form (or zwitterion; see Fig. 3-9) below, draw the chemical structures of the other two forms of alanine that predominate in aqueous solution: the fully protonated form and the fully deprotonated form. COO- H3N-C-H CH3 Alanine Of the three possible forms of alanine, which would be present at the highest concentration in solutions of the following pH: (b) 1.0; (c) 6.2; (d) 8.02; (e) 11.9. Explain your answers in terms of pH relative to the two pK₁ values. TABLE 3-1 Properties and Conventions Associated with the Common Amino Acids Found in Proteins Amino acid Abbreviation/ symbol pK₁ pk, values pK, pK M," (COOH) (NH) (R group) Nonpolar, aliphatic. ام Hydropathy index Occurrence in proteins (%) R groups Glycine Gly G 76 2.34 9.00 5.97 -04 72 Alanine Ala A 89 2.34 9.69 6.01 1.8 78 Proline Pro P 115 1.90 10.96 6.48 -1.6 5.2 Valine Val V 117 2.32 9.62 5.97 4.2 6.6 Leucine Leu L 131 2.30 9.60 5.08 38 9.1 Isoleucine lle I 131 2.36 9.68 6.02 4.5 6.3 Methionine Met M 149 2.28 9.21 5.74 1.9 23 Aromatic В groups Phenylalanine Phe F 165 1.83 9.13 548 28 3.9 Tyrosine Tyr Y 181 2.20 9.11 10.07 5.60 -13 3.2 Tryptophan Trp W 204 2.38. 9.39 5.89 -0.9 141 Polar, uncharged R groups Serine Ser S 105 2.21 9.15 5.68 -0.8 6.8 Threonine Thr T 119 2.11 9.62 5.87 -0.7 5.9 Cysteine Cys C 121 1.96 10.28 8.18 5.07 2.5 1.9 Asparagine. Asn N 132 2.02 8.80 541 -3.5 4.3 Glutamine Gln Q 146 2.17 9.13 5.65 -3.5 4.2 Positively charged R groups Lysine Lys K 146 2.18 8.95 10.53 9.74 -3.9 5.9 Histidine. His H 155 1.82 9.17 6.00 7.59 -3.2 23 Arginine Arg R 174 2.17 9.04 12.48 10.76 -4.5 5.1 Negatively charged R groups Aspartate Asp D 133 1.88 9.60 3.65 2.77 -3.5 5.3 Glutamate Glu El 147 2.19 9.67 4.25 3.22 -3.5 6.3 33 "M, values reflect the structures as shown in Figure 3-5. The elements of water (M, 18) are deleted when the amino acid is incorporated into a polypeptide dbuchtof Rome. The values reflect the free enemi(16) of transfer of the amino acid side chain from a hydrastis solvent to water. This