Multiple Choice Questions 1. The purity of an enzyme at various stages of purification is best measured by: a. Total protein b. Total enzyme activity c. Specific activity of the enzyme d. Percent recovery of protein e. Percent recovery of the enzyme 2. Which would be best to separate a protein that binds strongly to its substrate? a. Gel filtration b. Affinity chromatography c. Cation exchange d. Anion exchange e. Cation or anion exchange 3. How many hydrogen bonds can a water molecule potentially take in liquid form? a. one b. two c. three d. four e. none of the above 4. How does the hydrophobic effect influence the structures of large molecules? a. Nonpolar molecules are not easily solubilized in water and aggregate b. Polar groups are oriented on the surface, interacting with the water c. Nonpolar molecules can mask the polar characteristics of the hydrophilic molecules d. a) and b) e. a) and c) 5. The most important buffering system for maintaining proper blood pH is: a. the charges on the amino acids b. the bicarbonate buffer system of CO2, carbonic acid, and bicarbonate c. phosphate groups of serum phosphoproteins d. none of the above e. all of the above 6. Myoglobin binding of oxygen depends on: a. the oxygen concentration (pO2) b. the hemoglobin concentration c. the affinity of myoglobin for the O2 (K) d. a) and c) e. a), b) and c)7. In the α 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 8. In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as: a. hyperbolic b. linear with a negative slope c. linear with a positive slope d. random e. sigmoidal 9. Which of the following is true about the properties of aqueous solutions? a. A pH change from 5.0 to 6.0 reflects an increase in the hydroxide ion concentration ([OH-]) of 20%. b. A pH change from 8.0 to 6.0 reflects a decrease in the proton concentration ([H+]) by a factor of 100. c. Charged molecules are generally insoluble in water. d. Hydrogen bonds form readily in aqueous solutions. e. The pH can be calculated by adding 7 to the value of the pOH. 10 The Henderson-Hasselbalch equation: a. allows the graphic determination of the molecular weight of a weak acid from its pH alone. b. does not explain the behavior of di- or tri-basic weak acids c. employs the same value for pKa for all weak acids d. is equally useful with solutions of acetic acid and hydrochloric acid e. relates the pH of a solution to the pKa and the concentrations of acid and conjugate base 11. Two amino acids of the standard 20 contain sulfur atoms. They are: a. cysteine and serine b. cysteine and threonine c. methionine and cysteine d. methionine and serine e. threonine and serine12. An octapeptide composed of four repeating glycylalanyl units has: a. one free amino group on an alanyl residue b. one free amino group on an alanyl residue and one free carboxyl group on a glycyl residue c. one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue d. two free amino and two free carboxyl groups e. two free carboxyl groups, both on glycyl residues 13. In a mixture of the five proteins listed below, which should elute second in size-exclusion (gel filtration) chromatography? a. cytochrome c Mr = 13,000 b. immunoglobulin G Mr = 145,000 c. ribonuclease A Mr = 13,700 d. RNA polymerase Mr = 450,000 e. serum albumin Mr = 68,500 14. The enzyme fumarase catalyzes the reversible hydration of fumaric acid to l-malate, but it will not catalyze the hydration of maleic acid, the cis isomer of fumaric acid. This is an example of: a. biological activity b. chiral activity c. racemization d. stereoisomerization e. stereospecificity 15. The first step in two-dimensional gel electrophoresis generates a series of protein bands by isoelectric focusing. In a second step, a strip of this gel is turned 90 degrees, placed on another gel containing SDS, and electric current is again applied. In this second step: a. proteins with similar isoelectrip points become further separated according to their molecular weights. b. the individual bands become stained so that the isoelectric focus pattern can be visualized c. the individual bands become visualized by interacting with protein-specific antibodies in the second gel d. the individual bands undergo a second, more intense isoelectric focusing e. the proteins in the bands separate more completely because the second electric current is in the opposite polarity to the first current16. 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 Cα-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 17. The major reason that antiparallel β-stranded protein structures are more stable than parallel β-stranded structures is that the latter a. are in a slightly less extended configuration than antiparallel strands b. do not have as many disulfide crosslinks between adjacent strands c. do not stack in sheets as well as antiparallel strands d. have fewer lateral hydrogen bonds than antiparallel strands e. have weaker hydrogen bonds laterally between adjacent strands 18. Experiments on denaturation and renaturation after the reduction and reoxidation of the –S-S- bonds in the enzyme ribonuclease (RNase) have shown that: a. folding of denatured RNase into the native, active conformation requires the input of energy in the form of heat b. native ribonuclease does not have a unique secondary and tertiary structure c. the completely unfolded enzyme, with all –S-S- bonds broken, is still enzymatically active d.