B1_MidtermExam1_2023_QUESTIONS_CompleteKey_updated101323

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Jan 9, 2024

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Page 1 of 10 BIOCHEMISTRY I (CHEM-UA 881) Fall 2023 MIDTERM EXAM 1, Oct. 6, 2023 One point extra credit for completing the 3 lines below properly NAME : ___________________________ N-NUMBER : __________________________ TA & RECITATION TIME : __________________________ PLEASE WRITE LEGIBLY & BE CONCISE. Your answers must be your own! No calculators, no use of electronic devices, no communication between students. Partial credit will be given. (There are a total of 9 pages in the exam, including this page) USEFUL INFORMATION: Group Typical pKa Terminal a -carboxyl group 3 Aspartic acid/Glutamic acid 4 Histidine 6 Terminal a -amino group 8 Cysteine 8 Tyrosine 10 Lysine 11 Arginine 12 USEFUL EQUATION: pH = pKa + log([A - ]/[HA]) QUESTION PTS YOUR SCORE 1 30 2 25 3 10 4 10 5 15 6 10 TOTAL 100
Page 2 of 10 1. Multiple Choice. Circle the correct answer for each. ( 3 points each; 30 total ) i. Which of the following statements is TRUE about Anfinsen’s famous folding experiments on RNAse A? a. Anfinsen concluded that the primary sequence of a protein alone is sufficient to determine structure. b. Formation of protein disulfide bonds alone was enough to restore the activity of RNAse A. c. Addition of urea returned RNAse A to its native folded and active state. d. Disulfide bonds in RNAse A could be formed with the addition of beta- mercaptoethanol. ii. Cystic Fibrosis can be considered a protein folding disease associated with an amino acid mutation. What best describes the effect of the altered protein folding? a. Gain of function b. Loss of function c. Cooperative function d. None of the above iii. What is the characteristic sequence of the alpha-helical keratin protein? (Hyp= hydroxyproline) a. Repeating (Gly-Pro-Pro) b. Repeating (Gly-Hyp-Pro) c. Repeating (Gly-Pro-Hyp) d. Repeating (Gly-Gly-Hyp) e. None of the above iv. Disulfide bonds represent important ____________ that influence protein tertiary structure stability. a. non-covalent interactions b. van der Waals interactions c. hydrogen bonds d. salt bridges e. covalent bonds v. On average, what percentage of lysine residues in a peptide are present in the charged form at pH = 8? a. 99% (actually 99.9%) b. 90% c. 50% d. 10% e. 1%
Page 3 of 10 vi. Which of the following non-covalent interactions is driven primarily by changes in entropy ( D S)? a. Hydrogen bonding b. Hydrophobic effect c. Cation-pi interactions d. van der Waals interactions e. Electrostatic interactions vii. In a protein structure, which amino acid is the most likely to exhibit variation in the omega dihedral angle? a. Tryptophan b. Cysteine c. Glycine d. Proline e. Arginine viii. Which of the following amino acid residues would most likely be found in the interior of a water-soluble, globular protein? a. Glu b. Asp c. Lys d. Arg e. Ile ix. Which of the following proteins does not represent a fibrous protein? a. Silk fibroin b. Keratin c. Myoglobin d. Collagen e. None of the above
Page 4 of 10 x. In recitation, we discussed dihedral angle determination using the following amino acid depiction: Which of the following is true about the dihedral angle represented by atoms 1-4? (1 = N, 2 = C, 3= C, 4= N) a. The angle is f (“phi”), and it equals 0 ° b. The angle is f (“phi”), and it equals 180 ° c. The angle is y (“psi”), and it equals 0 ° d. The angle is y (“psi”), and it equals 180 ° e. The angle is w (“omega”), and it equals 180 ° 2 1 3 4 N N C C O
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