MetMetMultiple Choice 1. Citric acid → H+ + citrate- Citrate- → H+ + citrate2- Citrate2- → H+ + citrate3- Acids pK’s at 25°C Citric acid 2.15 Citrate- 4.76 Citrate2- 5.40 Given the above information, which statement(s) is/are most true if the pH of a citric acid solution is 5.08? a. [citrate-] > [citrate2-] b. [citrate-] = [citrate2-] c. [citrate-] < [citrate2-] d. [citrate2-] > [citrate3-] e. Both a and d 2. N-2-Hydroxyethylpiperazine-N’-2-ethanesulfonic acid (HEPES) has a pK of 7.47 in water. What would happen if HEPES was dissolved in formamide? Dielectric constant of water = 78.5 Dielectric constant of formamide = 110.0 a. The pK of HEPES decreases b. The pK of HEPES increases c. HEPES ions coalesce to form a salt d. Both a and c e. Both b and c 3. As climbers approach the summit of a mountain they usually increase their rate of breathing to compensate for the “thinner air” due to the oxygen pressures at higher elevations. This increased ventilation rate results in a reduction in the levels of CO2 dissolved in the blood. Which of the following accurately describes the effect of lowering the [CO2]dissolved on blood pH? a. It will result in an increase in the dissociation of H2CO3 → H+ + HCO3- and a drop in the pH. b. It will result in an increase in the dissociation of H2CO3 → H2O + CO2 and a drop in pH. c. It will result in an increase in the association of H+ + HCO3- → H2CO3 and an increase in pH. d. It will result in a decrease in the association of H+ + HCO3- → H2CO3 and a decrease in pH. e. Lowering [CO2]dissolved has no effect on blood pH. 4. Histidine in an aqueous solution with a pH of 8 a. has a net charge of -1 b. has a net charge of zero c. has a net charge of +1 d. is a zwitterions e. both b and d5. In gel filtration, a. large molecules have a longer path through the column. b. excess ligand is added to free the protein from the column. c. proteins are separated based on charge. d. an electric field is applied that causes migration of ions. e. the size of a protein can be analyzed. 6. In two-dimensional gel electrophoresis, what properties of proteins are exploited? a. density b. ionic charge c. molecular size d. both a and b e. both b and c 7. DEAE-cellulose a. is a ligand b. polymerizes to form a gel c. is a detergent d. is an anion exchanger e. is a cation exchanger 8. CYTKAVMWEFRDGMQKPNS You exposed the polypeptide to cyanogen bromide. You also exposed the polypeptide to trypsin. What fragments would you expect to find? a. AVMWEFR, CYTK, CYTKAVM, DGMQK, PNS, QKPNS, WEFRDGM b. AVMWEFR, CY, CYTK, DGMQK, DGMQKPNS, EF, R, PNS, TKAVMW c. CY, CYTKAVM, DGMQKPNS, EF, R, QKPNS, TKAVMW, WEFRDGM d. CY, CYTKAVM, EF, RDGMQKPNS, QKPNS, TKAVMW, WEFRDGM e. CY, DGMQKPNS, EF, R, RDGM, M, QKPNS, TKAV, TKAVMW, W9. Most screens for finding protein crystallization conditions are done by the “____________” method, mixing about _______ microliters each of the protein and the precipitant solutions where the protein is at about ________ mg/mL. a. batch / 1/ 1 b. hanging drop / 200 / 1 c. dialysis / 20 / 20 d. hanging drop / 3 / 15 e. hanging drop / 5 / 50 10. The resolution of a typical X-ray structure reported in the literature is about _____________, compared to the image obtained by negative stain electron microscopy that is about ____________ resolution. a. 1 nm / 10 nm b. 0.25 nm / 2.5 nm c. 0.1 nm / 1 nm d. 10 nm / 1 nm e. 0.20 nm / 0.20 nm 11. A peptide bond is all of these except: a. an ester bond b. a special type of amide bond c. a very stable type of amide bond d. formed when water is split out from an amino group and a carboxylic acid e. a bond which displays resonance 12. All of the following statements concerning β-sheets are true except: a. hydrogen bonds occur between neighboring polypeptide chains b. amino acid residues extend above and below β-sheets c. β-sheets exist at least numbers of two d. parallel β-sheets are more stable than antiparallel β-sheets e. β-sheets have an inherent right-handed twist 13. Which of the following is a/are characteristic(s) of collagen? Collagen: a. is “stretchy” due to its helical structure b. exists as a right-handed triple helical cable c. contains crosslinked disulfide bonds between cysteine residues d. both a and b e. both b and c14. What is the major determining factor for a protein’s three-dimensional structure? a. primary structure b. secondary structure c. tertiary structure d. quaternary structure e. hydrophobic interactions 15. The three-dimensional structure of macromolecules is formed and maintained primarily through noncovalent interactions. Which of the following is not considered a noncovalent interaction? a. hydrogen bonds b. van der Waals interactions c. disulfide bonds d. ionic interactions e. hydrophobic interactions 16. Which of the following is not an example of a folding accessory protein? a. peptidyl prolyl cis-trans isomerase b. GroEL/ES c. lysyl oxidase d. protein disulfide isomerase e. heat shock protein 60 17. The sugar maltose contains the following simple sugars: a. galactose b. glucose c. fructose d. both a and b e. both b and c 18. In regard to the YO2 versus pO2 graph, the effect of high levels of BPG would cause a shift to the ___________ of the ____________ curve. a. right / hyperbolic b. left / hyperbolic c. right / sigmoidal d. left / sigmoidal e. There would be no change.19. The Levinthal “golf course” landscape theory of protein folding a. shows that as a protein forms more intrachain contacts, internal energy of the protein decreases with its conformational freedom. b. shows that the protein randomly searches for its native conformation until it reaches a “canyon” in the energy surface and then the protein follows a particular pathway until it reaches it energy minimum. c. shows that there is a rugged energy surface containing local minima in which the folding protein can become trapped. d. shows that the protein chain randomly searches