Practice Questions Protein Structure

1. The amino acid sequence of a polypeptide is referred to as ________structure. a) Primary b) Secondary c) Tertiary d) Quaternary e) Peptide

A

20. What observation about protein refolding or renaturation helped to solidify the connection between primary amino acid sequence and 3-D structure? a) Spontaneous refolding of proteins into their native state under physiologic conditions. b) Assisted refolding of proteins into their native state under laboratory conditions. c) Identification of thermostable proteins than maintain their native state in adverse temperatures. d) A and B e) B and C

A

21. Based on what you know about fibrous protein structure and sequence, what type of fibrous protein is this sequence most likely to from (You can assume that the protein is longer than what is shown and is repeating as shown, also note the polarity of each amino acid.)? Val - Cys - Lys - Val - Cys - Ala - Cys - Val - Cys - Lys - Val - Cys - Ala - Cys a) α keratin b) collagen c) silk fibroin d) This sequence cannot be from any of the structural proteins. e) All of the above proteins can have this sequence

A

3. In the -helix the hydrogen bonds: a) are roughly parallel to the axis of the helix. b) are roughly perpendicular to the axis of the helix. c) occur mainly between electronegative atoms of the R groups. d) occur only between some of the amino acids of the helix. e) occur only near the amino and carboxyl termini of the helix.

A

8. Which of the following statements concerning the process of spontaneous folding of proteins is false? a) It may be an essentially random process. b) It may be defective in some human diseases. c) It may involve a gradually decreasing range of conformational species. d) It may involve initial formation of a highly compact state. e) It may involve initial formation of local secondary structure.

A

10. Keratin is classified as which of the following types of protein? a) Enzyme b) Structural c) Movement d) Defense e) Regulatory

B

14. Which one of these characteristics is not true for the a-helix? a) There are 3.6 amino acids per turn. b) There is a requirement for glycine every third amino acid residue. c) A hydrogen bond forms between the carbonyl oxygen of the nth amino acid residue and the NH group of the (n + 4)th amino acid residue. d) Proline is typically not found in the a-helix. e) It is right-handed.

B

17. Of the following, which amino acid is most likely to be found in position 1 or 4 on α keratin? a) Gly b) Ala c) Lys d) Gln e) Pro

B

4. In an -helix, the R groups on the amino acid residues: a) alternate between the outside and the inside of the helix. b) are found on the outside of the helix spiral. c) cause only right-handed helices to form. d) generate the hydrogen bonds that form the helix. e) stack within the interior of the helix.

B

11. Draw the molecular structure of the peptide Ala-Ser-His-Glu-Leu at pH 8 a) Mark all the peptide bonds in the peptide b) What is the net charge of the peptide at pH 6? c) What is the pI of the above peptide? Assume the following pKa values: 9.5 (Ala-NH2), 6.0 (His), 4.0 (Glu), 2.0 (Leu-COOH)

B- 0.5, 11C, 5.0

13. In a protein, the most conformationally restricted amino acid is ______; the least conformationally restricted is ______. a) Trp, Gly b) Met, Cys c) Pro, Gly d) Ile, Ala e) Ala, Pro

C

18. Which of the following amino acids combinations have side chains with complimentary groups that have the greatest ability to stabilize the tertiary structure of a protein? a) Lys and Arg b) Cys and Glu c) Glu and Lys d) Gln and Glu e) Pro and Asp

C

19. In general molecular chaperone proteins function by a) mediating disulfide bond formation b) synthesizing new proteins when one is misfolded. c) preventing premature folding by binding hydrophobic regions of the protein. d) enhancing salt bridge formation. e) none of the above

C

2. The overall three-dimensional structure of a polypeptide is referred to as _________ structure. a) Primary b) Secondary c) Tertiary d) Quaternary e) Peptide

C

7. Amino acid residues commonly found in the middle of a -turn are: a) Ala and Gly. b) hydrophobic. c) Pro and Gly. d) those with negatively charged R-groups. e) two Cys.

C

16. In the absence of ascorbic acid, prolyl oxidase is unable to oxidize proline residues in collagen to hydroxyproline, resulting in: a) lathyrism b) prion diseases c) amyloid formation d) scurvy e) allysine

D

22. Which of the following lines in the figure at right indicates a beta hairpin (beta turn) structure? a) A, C, D b) B and C c) A only d) A, B, and D e) C only

D

23. A helix has hydrogen bonds between the carbonyl group from residue "n" and the amino group of residue "n+6," which of the following is TRUE? a) It has 3.6 residues per turn. b) It is a random coil, not a helix. c) It is an α helix. d) It has more residues per turn than an α helix. e) It has fewer residues per turn than an α helix.

D

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.

D

12. Fibrous proteins typically have large amounts of: a) a-Helix b) beta-Pleated sheets c) Disulfide bridges d) Salt bridges e) Both A and B are correct

E

15. Which of the following changes would not alter the functional characteristics of α keratin? a) Increasing the number of residues per turn to 4.1 while maintaining the same amino acid sequence. b) Substitution of a hydrophobic amino acid for a hydrophilic amino acid at position a and d of the 7-residue pseudorepeat. c) Decreasing the number of cysteine amino acids within each protofilament. d) Changing the environment surrounding the protein to one that is more reductive. e) All of the above would alter the functional characteristics of keratin.

E

6. Which of the following interactions does not stabilize tertiary structure? a) Hydrophobic interactions b) Electrostatic interactions c) Hydrogen bonds d) Covalent bonds e) None of the above

E

9. Which of these characteristics does not describe the sheet? a) Amino acid side chains are located both above and below the sheet. b) sheets have a pleated edge-on appearance. c) They can exist in either parallel or antiparallel configurations. d) The sheets contain as few as two and as many as 22 polypeptide chains. e) Parallel sheets are more stable than anti-parallel sheets.

E