1665771052_773__practice_midterm_2

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Simon Fraser University *

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222

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Biology

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Dec 6, 2023

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pdf

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1 Practice midterm exam 2 (Fall 2022 – IK) Section 1: Multiple Choice Questions. Choose ONE best answer to each question. 1 mark each. 1. A protein's activity is altered when a particular serine side chain is phosphorylated. Which of the following amino acid substitutions at this position is likely to lead to a similar alteration in normal enzyme activity? A. S à Y B. None of the answers is correct C. S à T D. S à E 2. Which pairs of bonds within a peptide backbone show free rotation around both bonds? A. C a —C and N—C a B. C=O and N—C C. N—C a and N—C D. N—C and C a —C 3. Which statement is false? A. Collagen is a protein in which the polypeptides are mainly in the a -helix conformation. B. Disulfide linkages are important for keratin structure. C. Gly residues are particularly abundant in collagen. D. Silk fibroin protein consists of layers of anti-parallel β sheets. 4. You are studying an oligopeptide composed of eight amino acids at pH=7. The four amino acids nearest the C terminus are non-polar. The two amino acids nearest the N terminus are charged. The middle two amino acids are polar. Which amino acid is likely to be labeled as number 2? A. Threonine B. Lysine C. Glutamine D. Phenylalanine. 5. The following peptides are separated using an anion exchange resin in ion-exchange chromatography. Which peptide is eluted first? Peptide Molecular Weight (g/mol) Charge A 360 -2 B 1080 -1 C 1800 0 D 1440 + 1 A. A B. B C. C D. D
2 6. Which peptide would migrate the fastest in a SDS-PAGE gel? Peptide Molecular Weight (g/mol) A 360 B 1080 C 1800 D 1440 A. A B. B C. C D. D 7. Protein S will fold into its native conformation only when protein Q is also present in the solution. However, protein Q can fold into its native conformation without protein S. Protein Q, therefore, may function as a __________________ for protein S. A. proteasome B. molecular chaperone C. protein precursor D. structural motif 8. This protein is a homodimer of two helical polypeptides that are wrapped around each other to form what is called a coiled coil. A. collagen B. porin C. keratin D. fibroin 9. Protein secondary structures such as a -helices and b -sheets are stabilized mainly by A. ionic interactions. B. disulfide bridges. C. van der Waals forces. D. hydrogen bonds. 10. 7. At pH =4, what is the overall charge of the dipeptide shown below? (Use the pK a values as given below in the Figure). A. 0 B. -1 C. +1 D. -2
3 11. Which represents the correct arrangement of bonding in a peptide bond? A. B. C. D. 12. An a -helix has the sequence: NH3 + -Ser-Glu-Gly-Asp-Trp-Gln-Leu-His-Val-Phe-Ala-Lys-Val-Glu-COO - . In this a -helix, the carbonyl oxygen (in the peptide bond) of the histidine residue is hydrogen bonded to the amide nitrogen of A. Asp B. Lys C. Trp D. Ala 13 . In a polypeptide chain, the f and Y angles are the A. angles of peptide bonds. B. torsion angles on either side of the a -carbon. C. angles of each amino acid side chain. D. angles of a -helices. 14. All of the following are stabilizing forces in maintaining a stable protein tertiary (3°) structure, EXCEPT A. H bonds. B. temperature. C. hydrophobic interactions. D. electrostatic attraction.
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