50. Protein structural motifs often have general functions in common. Which one of the following motifs is known to be involved in protein dimer formation, but not in direct protein-DNA interactions?
(A) B-barrel.
(D) leucine zipper.
(B) helix-turn-helix.
(E) zinc finger.
(C) homeodomain.

1. Evidence that a peptide bond displays resonance includes all of these reasons, except:(A) It is planar. (B) It is shorter than a normal N-C single bond. (C) The alpha carbons attached to the peptide bond are always in a cis configuration. (D) It has double bond character. (E) All of these facts are consistent with peptide bonds displaying resonant structures.

2. Assuming the oligopeptide ALPHAHELICKS forms one continuous a-helix, the carbonyl oxygen of the glutamic acid residue is hydrogen bonded to the amide nitrogen of: (A) leucine. (B) isoleucine. (C) serine. (D) lysine. (E) cysteine.

3. Quaternary structure is associated with the relative orientation of one polypeptide to another polypeptide in a multisubunit protein. Which of the following bond forces are important in quarternary structure: (A) Disulfide bonds. (B) Hydrogen bonds. (C) Hydrophobic attraction. (D) Both hydrogen bonds and hydrophobic attraction. (E) All of these are important in quarternary structure.

4. In allosteric interactions: (A) proteins that consist of a single polypeptide chain form aggregates. (B) disulfide bonds are broken. (C) changes that take place in one site of a protein cause drastic changes at a distant site. (D) metal ions always bind to the protein. (E) aid in the correct and timely folding of other proteins.

5.Which type of columns are affected by the ionic charge, shape, substrate-binding strength of a protein, respectively? (A) Gel filtration, affinity chromatography, cation or anion exchange. (B) Cation or anion exchange, gel filtration, affinity chromatography. (C) Affinity chromatography, gel filtration, cation or anion exchange. (D) Gel filtration, cation or anion exchange, affinity chromatography. (E) Cation or anion exchange, affinity chromatography, gel filtration.

6. Which of the following statements about acid and base catalysis is correct? (A) Glu normally acts as a general acid in an enzyme reaction at around neutral pH. (B) General acid can abstract a proton from a substrate. (C) The active-site His in chymotrypsin protease reaction plays both roles of general acid and general base. (D) The value of Cys side chain is around 6. (E) Metal ion such as can accept electrons to act as a Lewis base.

7. In a peptide bond, the angle of rotation around the -N bond is designated: (A) α. (B) B. (C) o. (D) y. (E) Y.

8. Which of the following methods can not be used to determine protein molecular mass under native or denatured state? (A) Mass spectrometer. (D) Size exclusion column. (B) SDS-PAGE. (C) Analytic ultracentrifuge. (E) Isothermal titration microcalorimeter.

9. Which of the following statements about enzyme inhibitors is not correct? (A) A competitive inhibitor binds to the substrate binding site. (B) A competitive inhibitor does not alter the of an enzyme reaction. (C) A competitive inhibitor increases the of an enzyme reaction. (D) A non-competitive inhibitor decreases the of an enzyme reaction. (E) A non-competitive inhibitor increases the of an enzyme reaction.

10. Which of the following strategies is not used by enzymes for effective catalysis? (A) Van der Waals catalysis. (B) Metal ion catalysis. (C) Covalent catalysis. (D) General acid and base catalysis. (E) Electrostatic catalysis.

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