There are 24 questions in all. Questions 1-20 are multiple choice and are each worth 3 points. Questions 21-24 are essays and problems worth a total of 40 points.

These are constants you may find helpful: R = 8.314 J/mole-K; T = 298 K

              1. Which solution has the highest [H⁺]? The one that has a pH =
(A) 2.5; (B) 4.3; (C) 8.1; (D) 9.7 .

              2. The pK_a for the α-amine of glycine is 9.60. What percentage of glycine molecules in solution at pH 9.0 have protonated α-amines (are in the HA form)?
(A) 20%; (B) 25%; (C) 75%; (D) 80%.

3-4. Tyrosine pK_a's are 2.20 for the α-COOH, 9.11 for the α-amine, and 10.07 for the side chain.

              3. In a protein, a tyrosine side chain near a          side chain would have a pK_a that is
                   than 10.07 .   (A) serine, higher; (B) glutamate, lower;
(C) phenylalanine, higher; (D) lysine, lower.

              4. Most tyrosine molecules in solution have a net charge = 0 over the pH range
(A) less than 2.0; (B) 2.4-9.0; (C) 9.2-9.9; (D) greater than 10.2.

              5. When a water molecule associates with this molecule, the circled atom could be a
(A) hydrogen donor; (B) hydrogen acceptor; (C) neither, because this would not form a hydrogen bond.

              6. Which amino acid has this titration curve?
(A) alanine; (B) aspartate; (C) histidine; (D) arginine.

              7. This is the amino acid                , which has been modified by adding a/n                                                .
(A) isoleucine, amine; (B) arginine, carboxyl;
(C) methionine, carboxyl; (D) lysine, methyl.

              8. The steps of the Edman degradation include modifying the                                  , hydrolyzing                           peptide bond(s), and identification of                       .
(A) amine terminus, all, all residues;
(B) amine terminus, the first, the modified residue;
(C) carboxyl terminus, all, all residues;
(D) carboxyl terminus, the last, the modified residue.

              9. During sequencing, proteins must be broken into smaller fragments prior to Edman degradation because the Edman degradation can only be used for
(A) about 50-residue segments; (B) identifying one residue at a time;
(C) non-aromatic residues; (D) denatured proteins.

              10. These four sequences include all twenty amino acids. (1) S-W-N-Q-Y;
(2) C-L-A-M-P; (3) T-H-I-R-D; (4) K-F-G-V-E.                         
When the sequences are ranked in order of increasing polarity (most polar last), they are
(A) 1 → 2 → 3 → 4; (B) 2 → 1 → 4 → 3; (C) 2 → 4 → 1 → 3; (D) 1 → 4 → 3 → 2.

              11. Chaperones are                           that use                       in order to                           .
(A) proteins, mercaptoethanol, break disulfide bonds;
(B) organelles, ATP, form disulfide bonds correctly; (C) proteins, ATP, fold proteins correctly; (D) bacteria, heat, denature proteins in host cells.

              14. The ribonuclease denaturation experiment demonstrated several things. Which of these choices was not shown by the experiment?
(A) a protein can be denatured and still function; (B) the primary structure of the protein determines its other levels of structure; (C) disulfide bonds can be broken and then re-form correctly;
(D) denaturation is not always irreversible.

              15. As a result of the reaction catalyzed by carbonic anhydrase, hemoglobin in red blood cells traveling through lung capillaries                                H⁺ and is stabilized in the                           conformation. (A) binds, R; (B) binds, T; (C) releases, R; (D) releases, T.

              16. H⁺ that binds to a hemoglobin molecule usually binds to
(A) a histidine side chain; (B) a heme, but not to Fe²⁺; (C) Fe²⁺ in a heme;
(D) the COO^- terminal of the α chain.

              17. Both X and Y are graphic representations of O₂-binding by hemoglobin. In X,
the solid line shows           , the dashed line shows             , and the x axis is          .
(A) Hb, Mb, % binding sites occupied; (B) Hb, Mb, log pO₂;
(C) Mb, Hb, % binding sites occupied; (D) Mb, Hb, log pO₂.

              18. Diagram Y shows Hb only. (A) Adding BPG would move the curve to the left;
(B) Adding H⁺ would move the curve to the left; (C) The Mb curve would be on the left; (D) The Mb curve would be on the right.

              19. Both CO and CO₂ can bind hemoglobin and reduce O₂-binding. The difference is that (A) only CO binds heme; (B) only CO₂ binds heme; (C) both bind heme, but CO has a higher affinity; (D) both bind heme, but CO₂ has higher affinity.

              20. Diagram Z shows BPG bound to adult Hb (HbA), primarily to the β-chains. Fetal Hb is α₂γ₂, and the γ chain has Ser 143 rather than His 143. As a result, fetal Hb, compared to HbA,                                               and therefore has a                                           affinity for O₂.
(A) binds BPG more tightly, higher; (B) binds BPG more tightly, lower;
(C) is less likely to bind BPG, higher; (D) is less likely to bind BPG, lower.

21-23. Use sequence M: histidine-glycine-glutamine-aspartate-isoleucine-leucine-isoleucine-arginine .

21. Fill in the rest of the table. For class use (N) nonpolar; (A) aromatic;
(P) polar uncharged; (+) positively charged; or (-) negatively charged.

22. Draw the underlined residues in sequence M as a 4-residue peptide at pH 7.

      What is the pI for this peptide?                      

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