Exam I Answer Key: Summer 2006, Semester C

Transcription

1 1. Which of the following tripeptides would migrate most rapidly towards the negative electrode if electrophoresis is carried out at ph 3.0? a. gly-gly-gly b. glu-glu-asp c. lys-glu-lys d. val-asn-lys e. arg-arg-his 2. Which of the following dipeptides would not migrate in an electric field at ph 5.75? a. glu-glu b. arg-lys c. val-leu d. gly-asp e. phe-lys 3. The dipeptide gly-gly is sometimes used as a buffer. At which of the following ph values would you predict gly-gly would be most effective as a buffer? a. 2.0 b. 4.0 c. 6.0 d. 8.0 e A solution of M HCl, will have a ph between which of the following? a. 1-2 b. 2-3 c. 3-4 d. 4-5 e Which of the following would be the easiest and most efficient way to separate a single amino acid from a single protein [BEST ANSWER]? a. dialysis b. gel filtration c. centrifugation d. ion exchange chromatography e. affinity chromatography.

2 6. Some small polypeptide hormones are circular. That means that the terminal amino group and terminal carboxyl group are actually covalently bonded to each other to form a peptide linkage. How many peptide bonds would occur in a circular decapeptide? a. 8 b. 9 c. 10 d. 11 e Which of the follow is true about the binding of molecular (diatomic) oxygen to hemoglobin. a. the binding pulls Fe out of the plane of the porphyrin ring b. the binding pushes a histidine residue away from the ring c. the binding causes the oxygen molecule to bend d. oxygen binding displaces a sulfydryl sitting in the porphyrin ring e. only one oxygen molecule can bind to hemoglobin at a time 8. The following hexapeptides are hydrolyzed with strong acid, the resulting amino acids separated by thin layer chromatography and detected with ninhydrin. The products of which hexpeptide will show the most intense yellow spot? a. arg-arg-val-cys-cys-arg b. arg-cys-cys-cys-trp-trp c. cys-trp-pro-cys-trp-trp d. arg-pro-arg-arg-arg-trp e. pro-arg-arg-cys-cys-pro 9. Which of the following amino acids is most likely to found in a beta turn? a. glutamic acid b. methionine c. alanine d. proline e. leucine 10. If you treated the following peptide with trypsin, how many tripeptides would result? Arg-val-lys-arg-cys-tyr-lys-his-val-arg-gly-glu-lys a. none b. one c. two d.three e. four

3 11. If equal volumes of 0.1 M acetic acid (pk = 4.70) and 0.01 M sodium acetate are mixed, the final ph will be. a b c d e Which of the following procedures can be used for both protein purification and molecular weight determination of the native protein? a. dialysis b. affinity chromatography c. sodium dodecyl sulfate polyacrylamide gel electrophoresis d. gel filtration e. centrifugation 13. Which of the following dipeptides could theoretically exhibit the most optically active isomeric forms? a. val-cys b. leu-tyr c. gly-gly d. ile-thr e. leu-cys 14. Which of the following equations best describes how a buffer works? a. HCl H + + Cl - b. HCl + NaOH salt and water c. NH4+ OH - NH4OH d. Acetic acid + HCl H + + Cl - + acetic acid e. H2CO3 CO2 and H Which of the following tripeptides will remain most tightly bound to an anion (positively charged) ion-exchange resin at ph 7.5? a. glu-lys-lys b. met-val-val c. glu-asp-asp d. lys-arg-arg e. tyr-trp-met

4 16. The following reaction: R-S-S-R 2RSH is best described as a(n) a. oxidation b. reduction c. acidification d. enolization e. hydrolysis 17. The strongest hydrophobic interactions will occur between the side chains of: a. met and asp b. phe and arg c. leu and val d. gly and ser e. ser and thr 18. Disulfide bridges form between the side chains of: a. cysteine b. cystine c. methionine d. asparagine e. thioacetic acid 19. Hydrophobic amino acids are most likely to be highly populated a. on the N-terminus region of a protein b. on the C-terminus region of a protein c. on the surface of a protein d. in the interior of a protein e. in any region capable of hydrogen bonding 1. Ionic interactions in protein structure stabilize: a. primary structure b. secondary structure c. tertiary structure d. disulfide bridges e. planarity of the peptide bond

5 21. Which of the following ph values is closest to the isoelectric point of arginine? a. 2 b. 4 c. 6 d. 10 e What role does dicyclohexylcarbodiimide play in the solid support chemical synthesis of peptides? a. It is an insoluble matrix on which the polypeptide chain grows b. It is an essential solvent for formation of a peptide bond c. It is used as a blocking agent for the otherwise reactive alpha-amino group d. It is an activator of the amino acid carboxyl group e. It is a reagent used to release the completed peptide from the solid support 23. If 20 ml of 0.1 M sodium hydroxide is added to 220 ml of 0.1 M acetic acid (pk 4.7), what is the final ph? a b c d e How many moles of dinitrofluorobenze will react with one mole of the following peptide? Arg-val-lys-arg-cys-tyr-lys-his-val-arg-gly-glu-lys a. none b. one c. two d. three e. four 25. Which of the following names are associated with methods for determination of a protein s primary structure a. Merrifield only b. Merrifield and Sanger c. Merrifield, Sanger and Edman d. Merrifield and Edman e. Sanger and Edman

6 26. The side chains of which of the following pairs of amino acids cannot form hydrogen bonds with each other? a. ser and arg b. asp and lys c. gln and glu d. gly and thr e. his and asn 27. Phenyl isothiocyanate reacts specifically with: a. primary amines b. secondary amines c. cysteine d. cystine e. carboxylic acids 28. Which of the following reactions is known to be a slow step in folding of protein when compared with the other listed reactions? a. proline isomerization b. formation of a molten globule c. stereoisomeric interconversions of mirror images d. formation alpha helical structures e. formation of beta sheet structures 29. Beta sheet secondary structure of proteins is the result of: a. covalent crosslinks b. ionic interactions c. hydrophobic forces d. hydrogen bonds e. disulfide bridges 30. In the process of affinity chromatography, the most specific way to displace the bound protein is: a. changing ionic strength b. addition of soluble ligand c. increasing salt concentration d. apply a narrow and specific electric pulse e. wash the column with a buffer at a.ph value equivalent to the pk value of the weak acid component of the buffer. 31. Which of the following is NOT true for SDS-PAGE? a. Electrophoretic separation is based on size b. All proteins are denatured c. It can be used to determine the molecular weight of a multisubunit protein d. Must be stained to detect most proteins e. Uses polyacrylamide as a support matrix

7 32. Hemoglobin transports oxygen, while myoglobin binds oxygen. This difference is most directly attributed to differences in: a. the type of porphyrin ring b. the location of the iron c. the amount of alpha helical secondary structure d. the number of subunits e. the type of oxygen being bound 33. Which of the following tetrapeptides will NOT absorb light in the near ultraviolet region? a. val-leu-arg-met b. ile-tyr-arg-cys c. phe-his-lys-asp d. asn-glu-trp-gln e. met-phe-leu-asn Answers: 1. E 2. C 3. A 4. B 5. A 6. C 7. C 8. E 9. D 10. D 11. E 12. D 13. D 14. C 15. C 16. B 17. C 18. A 19. D 20. C 21. D 22. D 23. E 24. E 25. E 26. D 27. A 28. A 29. D 30. B 31. C 32. D 33. A