A typical amino acid with one amino group and one carboxylic acid group, such as serine (Figure 24.18), can exist in water in several ionic forms.
(a) Suggest the forms of theamino acid at low pH and at high pH.
(b) Amino acids generally have two pKa values, one in the range of 2 to 3 and the other in the range of 9 to 10. Serine, for example, has pKa values of 2.19 and 9.21. Using species such as acetic acid and ammonia as models, suggest the origin of the two pKa values.
(c) Glutamic acid is an amino acid that has three pKa's: 2.10, 4.07, and 9.47. Draw the structure of glutamic acid, and assign each pKa to the appropriate part of the molecule.