The isoelectronic point of an amino acid is the point where A

1. The isoelectronic point of an amino acid is the point where
   A. the amino acid carries no net electrical charge.
   B. the a-carboxylic acid is protonated and the a-amino group is unprotonate
   C. the pKa of the a-carboxylic acid is the same as the pKa of the a-amino group.
   D. the solubility of the amino acid is maximized.
   E. the a-carboxylic acid and the a-amino group are both half protonated.

A. the amino acid carries no net electrical charge.

2. Which of the amino acids represented below has two chiral centers?
   A. Asn
   B. Ala
   C. Pro
   D. Leu
   E. Ile

E. Ile

3. Name three amino acids that are positively charged at a neutral pH
   A. cys, arg, and met
   B. lys, arg, and his
   C. lys, arg, and pro
   D. his, arg, and cys
   E. arg, glu, and his

B. lys, arg, and his

4. In what pH range is zwitterionic Alanine the predominate structure?
   
   A. 9-14
   B. 8-10
   C. 0-2
   D. 2-9

D. 2-9

5. Which of the following amino acid residues would most likely be buried in the interior of a water soluble, globular protein?
   A. Lys
   B. Gln
   C. Asp
   D. Ser
   E. Phe

E. Phe

6. The pK1, pK2, and pKR of the amino acid histdine are 1.8, 9.3, and 6.0, respectively. The pK1, pK2, and pKR of the amino acid arginine are 1.8, 9.0, and 12.5, respectively. You have a mixture of histidine and arginine, how would you try to separate these two amino acids?
   A. cation exchange chromatography at pH 9
   B. anion exchange chromatography at pH 2
   C. cation exchange chromatography at pH 2
   D. anion exchange chromatography at pH 4
   E. cation exchange chromatography at pH 4

A. cation exchange chromatography at pH 9

7. The pK1, pK2, and pKR for the amino acid glutamate are 2.1, 9.5, and 4.1, respectively. At pH 11.0, glutamate would be charged predominantly as follows:
   A. a-carboxylate −1, a-amino 0, g-carboxylate −1, net charge −2
   B. a-carboxylate 0, a-amino 0, g-carboxylate 0, net charge 0
   C. a-carboxylate +1, a-amino 0, g-carboxylate +1, net charge +2
   D. a-carboxylate +1, a-amino −1, g-carboxylate +1, net charge +1
   E. a-carboxylate −1, a-amino +1, g-carboxylate −1, net charge −1

A. a-carboxylate −1, a-amino 0, g-carboxylate −1, net charge −2

8. What charged group(s) are present in glycine at a pH of 7
   A. NH3+
   B. COO-
   C. NH2+
   D. a and b
   E. a and b and c

D. a and b

9. The pK1, pK2, and pKR for the amino acid lysine are 2.2, 9.1, and 10.5, respectively. At pH 1.0, lysine would be charged predominantly as follows:
   A. a-carboxylate +1, a-amino +2, e-amino +2, net charge +5
   B. a-carboxylate −1, a-amino +1, e-amino +1, net charge +1
   C. a-carboxylate 0, a-amino +1, e-amino +1, net charge +2
   D. a-carboxylate 0, a-amino −1, e-amino −1, net charge −2
   E. a-carboxylate +2, a-amino +1, e-amino +1, net charge +4

C. a-carboxylate 0, a-amino +1, e-amino +1, net charge +2

10. The pK1, pK2, and pKR for the amino acid arginine are 1.8, 9.0, and 12.5, respectively. At pH 7.0 arginine would be charged predominantly as follows:
    A. a-carboxylate −1, a-amino +1, guanidino +1, net charge +1
    B. a-carboxylate −1, a-amino 0, guanidino +1, net charge 0
    C. a-carboxylate +1, a-amino 0, guanidino -1, net charge 0
    D. a-carboxylate +1, a-amino −1, guanidino −1, net charge −1
    E. a-carboxylate 0, a-amino 0, guanidino +1, net charge +1

A. a-carboxylate −1, a-amino +1, guanidino +1, net charge +1