An amino acid has pK1 2

1. An amino acid has pK1 2.5, pK2 9.4 and pKR 4.2. Calculate the isoelectric point for this amino acid.

Correct response: (3.4)

2. The pK1, pK2, and pKR for the amino acid cysteine are 1.9, 10.7, and 8.4, respectively. At pH 5.0, cysteine would be charged predominantly as follows:
   A. a-carboxylate −1, a-amino +1, sulfhydryl +1, net charge +1
   B. a-carboxylate −1, a-amino +1, sulfhydryl 0, net charge 0
   C. a-carboxylate +1, a-amino −1, sulfhydryl 0, net charge 0
   D. a-carboxylate 0, a-amino 0, sulfhydryl 0, net charge 0
   E. a-carboxylate +1, a-amino −1, sulfhydryl −1, net charge −1

B. a-carboxylate −1, a-amino +1, sulfhydryl 0, net charge 0

3. The tripeptide glycylarginylglutamate contains four ionizable groups with pKas of 2.1, 4.1 9.8, and 12.5. Calculate the pI for this molecule.
   A. 3.1
   B. 6.4
   C. 7.0
   D. 8.3
   E. 7.3

C. 7.0

4. Which of the following tripeptides would be expected to be the most hydrophobic?
   A. GYA
   B. DYG
   C. KYG
   D. KYA
   E. DYA

A. GYA

5. The tripeptide glycylarginylglutamate contains four ionizable groups with pKas of 2.1, 4.1 9.8, and 12.5. Calculate the pI for this molecule
   A. 6.4
   B. 3.1
   C. 7.0
   D. 7.3
   E. 8.3

C. 7.0

6. Which of the following tripeptides carries a net positive charge at pH 7.0?
   A. Leu?Lys?Gly
   B. Ala?Thr?Asn
   C. Arg?Glu?Met
   D. Gln?Val?Ser
   E. Pro?Ile?Leu

A. Leu?Lys?Gly

7. The overall charge of a peptide of the following peptide sequence at pH 1 would be (Asp-Gly-Arg-His):
   A. -3
   B. 0
   C. -1
   D. 3
   E. 1

D. 3

8. The tripeptide alanyllysylaspartate contains four ionizable groups with pKas of 2.0, 3.9, 9.9, and 10.5. Calculate the pI for this molecule.
   A. 3.0
   B. none of the given
   C. 6.0
   D. 6.2
   E. 10.2

B. none of the given

9. You are trying to separate five proteins, which are listed below, by gel filtration chromatography. Which of the proteins will elute first from the column?
   A. interferon-g (34 kDa)
   B. hemoglobin (62 kDa)
   C. glutamine synthetase (621 kDa)
   D. RNA polymerase (99 kDa)
   E. cytochrome c (12 kDa)

A. interferon-g (34 kDa)

10. Interactions between side chains of and Asp and Arg at neutral pH would be?
    A. hydrogen bonding
    B. hydrophobic
    C. ionic
    D. covalent

C. ionic