Name: __________________________________ NetID:_________________________ 1 MCB 450 Exam I September 22, 2014 Form A Choose the BEST answer from the available choices. Only non-graphing calculators are permitted for use on this exam. Part I: Multiple Choice (5 points each; 10 total): Record all of your answers on the scantron sheet. 1. What is the pKa of a weak acid, which is 10% deprotonated at pH 2.5? a. 1.75 b. 2.50 c. 3.25 d. 3.45 e. Cannot be determined from above information 2. A solution of 100 mM acetic acid (pKa 4.8) is prepared. Calculate the pH value of the buffer solution following the addition of 0.05 M NaOH. a. 4.5 b. 4.8 c. 5.1 d. 3.8 e. 5.8Name: __________________________________ NetID:_________________________ 2 Part II: Multiple Choice (4 points each; 120 total): Record all of your answers on the scantron sheet. 3. Which of the following pairs will not interact via a hydrogen bond? a. Hydroxyl group of threonine and water b. Carbonyl of a ketone and water c. Carbonyl and an amide nitrogen d. Methyl group and water e. Two water molecules 4. Properties of water that render it so suited to its role as a medium of life include all EXCEPT: a. Unrivaled ability to form hydrogen bonds. b. Unparalleled ability to orient around nonpolar solutes to promote hydrophobic interactions. c. Unusually high dielectric constant of water that increases the ions’ attraction for one another. d. The small, but significant, tendency to form H+ and OH- ions. e. None, all are true. 5. Hydrogen bonds can occur when the hydrogen is covalently bonded to atoms like nitrogen and oxygen (hydrogen-bound donors). What property of nitrogen and oxygen is important for this? a. Atomic mass b. Ionizability c. Hydrophobicity d. Electronegativity e. Greater number of unpaired electronName: __________________________________ NetID:_________________________ 3 6. The hydrophobic effect is primarily: a. Entropic, resulting in an increase in entropy of water molecules b. Enthalpic, resulting in an increase in enthalpy of solute molecules in water c. Entropic, resulting in an increase in entropy of solute molecules in water d. Enthalpic, resulting in a decrease in enthalpy of water molecules e. Entropic, resulting in a decrease in entropy of solute molecules in water 7. Buffers have all of the following characteristics EXCEPT: a. They have relatively flat titration curves at the pH(s) where they buffer. b. They resist changes in their pH as acid or base is added. c. They are typically composed of a weak acid and its conjugate base. d. They have the highest buffering capacity where the amounts of conjugate base are nearly equivalent to the amounts of weak acid. e. For polyprotic acids with two ionizable groups, they buffer best half-way between the two pKa values. 8. Which one of the forms of amino acids labeled a-e would you NOT expect to find in aqueous solution?Name: __________________________________ NetID:_________________________ 4 9. Asparagine in solution will have a net charge of zero at: (Please use the pKa table provided below) a. pH 8.0 b. a pH relatively close to the pKa of histidine’s imidazole N. c. pH 9.0 d. a pH relatively close to the pKa of lysine’s R-group. e. pH 2.1 10. Which one of the following peptides will show the strongest absorbance of UV light at a wavelength of 280 nm? a. HSIEFDGVNQL b. NQTRSTRHSLIA c. ESIALRIFPTVG d. HNSLRHMTPVR e. QHYHRWLNSYT 11. Which of the following statements about disulfide binds is NOT true: a. If present between two proteins, they would cause both to pass through a gel filtration column more quickly. b. They only form between two cysteine residues. c. They form in the presence HO-C2H4SH. d. They can form in 8 M urea if air is present. e. They can be formed between different pairs of cysteines in a polypeptide if 8 M urea is present.Name: __________________________________ NetID:_________________________ 5 12. Which column of five stick figures (columns a-e) shows the successive changes in protonation that occur when increasing amounts of base are added to the fully protonated peptide His-Lys-Trp? 13. Which of the following numbers is most likely to be the number of amino acids in a 65 kDa protein? (Assume there are no protein modifications.) a. 59 b. 650 c. 65 d. 591 e. 375Name: __________________________________ NetID:_________________________ 6 14. The following molecule has _______ peptide bonds, and rotation about the bond arrowed _____ is described by the Psi (ψ) torsion angle. a. 3 and III b. 4 and II c. 4 and III d. 3 and II e. 3 and I 15. Which of these statements about the 3-D structures of globular proteins is true? a. The only elements of secondary structure in domains are alpha helices b. A motif or fold can be made up of either alpha helices of beta strands but not both c. Amino acids responsible for catalytic activity of an enzyme can be located in alpha helices or beta-sheets d. Domains can have distinct or independent functions e. Their polar and ionizable amino acid side chains are usually in the interior of the protein. 16. Histones are described as “basic” proteins. This is because a. They contain high proportions of amino acids with simple, non-polar side chains such as glycine and alanine b. They are rich in arginine and lysine residues c. They have relatively low isoelectric points d. They are rich in aspartate and glutamate residues e. They would not be retarded on a deprotonated cation exchangerName: __________________________________ NetID:_________________________ 7 17. One of the dipeptides numbered 1-8 contains an amino acid with one of the side chain modifications discussed in class, and another of the dipeptides contains an amino acid that is not one of the standard amino acids. Which two peptides are they? a. 1 and 2 b. 2 and 4 c. 3 and 8 d. 4 and 5 e. 6 and 7Name: __________________________________ NetID:_________________________ 8 18. In an α-helix, the hydrogen bonds: a. are at right angles to the axis of the helix. b. occur mainly between electronegative atoms of the peptide’s R groups. c. occur mainly between the electronegative atoms of the peptide backbone. d. occur only between every third amino acid along the helix. e. occur only near the amino and carboxyl termini of the helix. 19. Which of the following statements about collagen is FALSE? a.
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