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

2. Which tripeptides carry a net positive charge at pH 7.0? (A) Ala-Thr-Asn (B) Gln-Val-Ser(C)Arg-Glu-Met(D) Pro-Ile-Leu (E) Leu-Lys-Gly

3. Of the 20 standard amino acids, only ______ is not optically active. The reason is that its side chain ______. (A) alanine； is a simple methyl group (B) glycine； is a hydrogen atom (C)glycine； is unbranched (D) lysine； contains only nitrogen (E) proline； forms a covalent bond with the amino group

4. Which of the following refers to particularly stable arrangements of amino acid residues in a protein that give rise to recurring patterns? (A) Primary structure (B) Secondary structure (C)Tertiary structure (D) Quaternary structure (E) None of the above

5. 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.

7. Thr and/or Leu residues tend to disrupt an α helix when they occur next to each other in a protein because: (A) an amino acids like Thr is highly hydrophobic. (B) covalent interactions may occur between the Thr side chains. (C)electrostatic repulsion occurs between the Thr side chains. (D) steric hindrance occurs between the bulky Thr side chains. (E) the R group of Thr can form a hydrogen bond.

8. The tripeptide glycylarginylglutamate contains four ionizable groups with pKas of 2.1, 4.1 9.8, and 12.5. Calculate the pI for this molecule. (A) 3.1 (B) 6.4 (C)7.0 (D) 7.3 (E) 8.3

9. The quantitation of proteins due to their absorbance at ~280 nm (UV region) is due to the large absorptivity of the ______ amino acids. (A) anionic (B) dansylated (C)cleaved (D) polar (E) aromatic

10. When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe2+ are occupied by: (A) one O atom and one amino acid atom. (B) one O2 molecule and one amino acid atom. (C)one O2 molecule and one heme atom. (D) two O atoms. (E) two O2 molecules.

11. Myoglobin and the subunits of hemoglobin have: (A) no obvious structural relationship. (B) very different primary and tertiary structures. (C)very similar primary and tertiary structures. (D) very similar primary structures, but different tertiary structures. (E) very similar tertiary structures, but different primary structures.

12. Which one of the following statements is true of enzyme catalysts? (A) Their catalytic activity is independent of pH. (B) They are generally equally active on D and L isomers of a given substrate. (C)They can increase the equilibrium constant for a given reaction by a thousand fold or more. (D) They can increase the reaction rate for a given reaction by a thousand fold or more. (E) To be effective, they must be present at the same concentration as their substrate.