QUIZ 2, BICH 410( MWF 1:50 PM), Friday, Oct. 6, 1995
Clearly circle the letter corresponding to your answer for each problem. There are seven problems, six of which count 3 points, and one is worth 2 points. No partial credit given for multiple-choice questions.
1) Experiments on denaturation and renaturation after reduction and reoxidation of the disulfide bonds in the enzyme ribonuclease (RNase) have shown that:
- A) the primary sequence of RNase is sufficient to determine the formation of a specific secondary and tertiary structure.
- B) the enzyme, dissolved in water, is thermodynamically stable relative to the mixture of amino acids whose residues are contained in RNase.
- C) native ribonuclease does not have a unique secondary and tertiary structure.
- D) the completely unfolded enzyme, with all disulfide bonds broken, is still enzymatically active.
- E) the folding of denatured RNase into the native, active conformation, requires the input of energy in the form of heat.
2) Which sequence of amino acids listed below is most likely to be in the middle of a collagen chain?
- A) -hydroxyproline-hydroxyproline-hydroxyproline-hydroxyproline-hydroxyproline-
- B) -hydroxyproline-glutamic acid- proline-proline-hydroxyproline-
- C) -proline-hydroxyproline-cysteine-glycine-proline-
- D) -hydroxyproline-glycine-proline-hydroxyproline-glycine-
- E) -glycine-leucine-proline-hydroxyproline-glycine-
3) Which of the following statements is true about alpha helices in proteins?
- A) The phi and psi angles for every amino acid subunit along the polypeptide chain are relatively constant.
- B) Every carbonyl carbon in the polypeptide backbone is involved in a hydrogen bond with the R- group of an amino acid subunit spaced four residues away.
- C) An electric dipole exists along the helix axis such that the carboxyl-terminal end is relatively more positively charged than the amino-terminal end.
- D) Proline residues stabilize the helix.
- E) Parallel alpha helices are aligned in an all right-handed sense, while antiparallel alpha helices are aligned in an alternating right- and left-handed sense.
4) How many hydrogen bonds connect the two ß strands given below when they exist in a parallel beta sheet?
5) (2 pts) Which substance is not chemically related to the heme group?
- A) bilirubin
- B) protoporphyrin IX
- C) lysinonorleucine
- D) biliverdin
- E) a heterocyclic compound containing iron
6) Positive cooperative binding of a ligand to a protein is always characterized by:
- A) the presence of a prosthetic group on the protein
- B) a Hill coefficient equal to 3
- C) a hyperbolic binding curve
- D) the decrease in binding affinity of a second ligand after binding of a first ligand
- E) a sigmoidal binding curve
7) Given the octapeptide sequence below, which statement is not true?
- A) Treatment with cyanogen bromide gives an octapeptide.
- B) The only derivative formed after reaction with fluorodinitrobenzene is DNP-cysteine.
- C) Treatment with trypsin results in three separate peptides.
- D) Treatment with chymotrypsin results in two peptides.
- E) The first round of Edman degradation gives PTH-cysteine