AdvBioCh4, MC - Chapter 4 The Three-Dimensional Structure...

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Chapter 4 The Three-Dimensional Structure of Proteins Multiple Choice Questions 1. All of the following are considered “weak” interactions in proteins, except: A) hydrogen bonds. B) hydrophobic interactions. C) ionic bonds. D) peptide bonds. E) van der Waals forces. 2. The most important contribution to the stability of a protein’s conformation appears to be the: A) entropy increase from the decrease in ordered water molecules forming a solvent shell around it. B) maximum entropy increase from ionic interactions between the ionized amino acids in a protein. C) sum of free energies of formation of many weak interactions among the hundreds of amino acids in a protein. D) sum of free energies of formation of many weak interactions between its polar amino acids and surrounding water. E) stabilizing effect of hydrogen bonding between the carbonyl group of one peptide bond and the amino group of another. 3. In an aqueous solution, protein conformation is determined by two major factors. One is the formation of the maximum number of hydrogen bonds. The other is the: A) formation of the maximum number of hydrophilic interactions. B) maximization of ionic interactions. C) minimization of entropy by the formation of a water solvent shell around the protein. D) placement of hydrophobic amino acid residues within the interior of the protein. E) placement of polar amino acid residues around the exterior of the protein. 4. Pauling and Corey’s studies of the peptide bond showed that: A) at pH 7, many different peptide bond conformations are equally probable. B) peptide bonds are essentially planar, with no rotation about the C—N axis. C) peptide bonds in proteins are unusual, and unlike those in small model compounds. D) peptide bond structure is extraordinarily complex. E) primary structure of all proteins is similar, although the secondary and tertiary
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2 Chapter 4 The Three-Dimensional Structure of Proteins structure may differ greatly. 5. In the diagram below, the plane drawn behind the peptide bond indicates the: A) absence of rotation around the C—N bond because of its partial double-bond character. B) plane of rotation around the C α —N bond. C) region of steric hindrance determined by the large C=O group. D) region of the peptide bond that contributes to a Ramachandran plot. E) theoretical space between –180 and +180 degrees that can be occupied by the φ and ψ angles in the peptide bond. 6. Which of the following best represents the backbone arrangement of two peptide bonds? A) C α —N—C α —C—C α —N—C α —C B) C α —N—C—C—N—C α C) C—N—C α —C α —C—N D) C α —C—N—C α —C—N E) C α —C α —C—N—C α —C α —C 7. Which of the following pairs of bonds within a peptide backbone show free rotation around both bonds? A)
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AdvBioCh4, MC - Chapter 4 The Three-Dimensional Structure...

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