Biology 263 Cell Biology
Joel Piperberg March 19, 2010
Second Exam Page # 10
Name ______
I. Multiple Choice. Fill in the circle on the test form corresponding to the correct answer.
For the next six questions you will need to refer to the structures of the amino acid R groups shown at the end of the multiple choice questions.
1. ______typically forms ______bonds between two different protein subunits?
a. Cysteine, covalent c. Cytosine, disulfide e. a and d
b. Glycine, H d. Methionine, disulfide
2. Which of the tripeptides below would be least soluble in a hydrophobic solvent like benzene?
a. N - phenylalanine - cysteine - glycine - C d. N - leucine - aspartate - glycine - C
b. N - proline - phenylalanine - leucine - C e. N - arginine - proline - alanine - C
c. N - glutamate - aspartate - lysine - C
3. Which of the amino acids listed below would be most likely to be found only on the interior of a polypeptide that has already adopted its active conformation and is in contact with the center of a lipid bilayer?
a. phenylalanine b. c and e c. aspartate d. leucine e. glutamate
4. Which amino acid would be likely to have a charge of -1 at physiological pH 7.4?
a. arginine b. lysine c. aspartate d. leucine e. a and b
5. Which amino acid would probably be found in the exterior of a protein in the cytoplasm?
a. aspartate b. methionine c. lysine d. a and c e. all of the other answers
6. Which amino acid has a positive charge at physiological pH?
a. methionine b. glutamate c. arginine d. b and c e. none of the above
7. What protein structure involves interaction between two portions of the same chain in the form of H bonds perpendicular to the axis of the molecule?
a. a-helix b. secondary c. a and b d. b-pleated sheet e. b and d
8. Which of the following may occur if an amino acid in the middle of an a-helix is changed from a helix-indifferent to a helix breaking amino acid?
a. The helix is strengthened. c. The helix ceases to exist. e. c and d
b. The helix becomes a b-pleated sheet. d. The protein's function is lost.
9. Non-denaturing gel electrophoresis has the advantage that it ______.
a. c and e
b. allows the detection of proteins in a gel by their biological activity
c. separates on the basis of more than one property thus to some degree confusing the results
d. separates solely on the basis of molecular weight
e. separates on the basis of molecular weight and charge
10. A protein applied to a gel moves steadily down the gel and stops before reaching the end while the current is still on. Why did the protein stop moving?
a. Its charge became positive. c. It was isometrically affected. e. It is denatured.
b. Its charge became negative. d. Its charge becomes neutral.
11. What kind of polypeptide structure involves interaction within the same chains in the form of H bonds perpendicular to the axis of the molecule?
a. primary b. secondary c. tertiary d. a-helix e. b and d
12. Which technique effectively separates proteins on the basis of their size, shape and density and also on the basis of the medium through which they are moving?
a. ion exchange chromatography c. non-denaturing gels e. SDS-PAGE
b. sucrose density gradient centrifugation d. a and b
13. The final protein conformation (the 3-D shape) is ultimately determined by ______.
a. the interaction between the R groups within the nucleic acid backbone
b. interaction between sphingolipid R groups
c. the interaction between adjacent or nearly adjacent regions of the carbohydrate backbone
d. the primary structure
e. all of the above
14. Which property below is typical of a-helical structure?
a. a high degree of extensibility b. flexibility c. strength d. rigidity e. b and c
15. Nucleation is most closely associated with which phenomenon below?
a. renaturation b. protein folding c. transcription d. translation e. a and b
16. What bonds are involved in holding together tertiary structure in proteins?
a. disulfide linkages c. H bonds e. a and c
b. hydronomic interactions d. peptide bond interactions
17. A protein you wish to study is located in the mitochondria of rat liver cells and is readily extractable from partially purified mitochondria. It has a highly negative charge at pH 7. You propose to use a series of techniques to purify the protein. In what order would you use the techniques after you had homogenized the tissue?
a. sucrose density gradient centrifugation (SDGF)- extraction - isoelectric focussing (IEF) -
precipitation by ammonium sulfate
b. differential centrifugation - SDGF - extraction - ammonium sulfate precipitation - CM
(carboxymethyl) cellulose chromatography - affinity chromatography
c. ammonium sulfate precipitation - SDGF - extraction - CM cellulose chromatography - IEF - SDGF
d. IEF - affinity chromatography - differential centrifugation - extraction
e. differential centrifugation- SDGF - extraction - ammonium sulfate precipitation - DEAE
(diethylaminoethyl) cellulose chromatography - affinity chromatography
18. The Unit Membrane model was shown to be inaccurate because ______.
a. all membranes were not exactly alike d. membranes vary in cholesterol content
b. membranes are made up of phospholipids e. a, c and d
c. membranes have different protein and lipid content
19. A protein is associated with the cell membrane and fully exposed to the extracellular environment of the cell. It can, however, be freed from the membrane by washing the cell with a low ionic strength salt solution. It is a ______protein.
a. peripheral b. extrinsic c. lipid-anchored d. transmembrane e. a and b
20. Resonance explains the ______of the ______bond that restricts the ability of a polypeptide to coil?
a. extensibility, peptide c. high rotational freedom, peptide e. a and d
b. rigidity, phosphate ester d. rigidity, peptide
21. If there are only different 20 amino acids inserted into proteins, how do amino acids, which are not among the twenty (like hydroxylysine and hydroxyproline), get into proteins?
a. They are added after synthesis. d. There really are 22 amino acids.
b. They are present before synthesis. e. none of the above
c. Amino acids inserted during synthesis are altered later.
22. Which technique could be used for molecular weight determinations in proteins under all circumstances?
a. gel filtration d. a and e
b. isoelectric focusing e. SDS-PAGE
c. carboxymethyl (CM) cellulose chromatography
23. What is the lowest level of polypeptide structure in a protein exhibiting subunit structure?
a. quaternary b. secondary c. tertiary d. a-helix e. primary
24. You are purifying a protein. Before you have employed any procedures to purify it, its specific activity is 300 units/mg protein. After 5 successive purification procedures, the specific activity is 12,000,000 units/mg protein How much have you purified the protein?
a. 40,000 times b. 4,000 times c. 400,000 times d. 0.00004 times e. .0004 times
25. What property of a protein can be determined directly with gel filtration chromatography if the protein is an oblate spheroid (cigar-shaped)?
a. molecular charge b. molecular weight c. molecular shape d. Stokes' radius e. b and d
26. If a solution containing the following tripeptides were passed through a column packed with CM-cellulose at pH 7, which of them would bind most effectively to the CM-cellulose column? (see drawing at end of Multiple Choice section for R groups)
a. N - arginine - lysine - proline - C d. N - leucine - alanine - glycine - C
b. N - aspartate - glutamate - aspartate - C e. N - aspartate - phenylalanine - leucine - C
c. N - phenylalanine - aspartate - glycine - C
27. Which technique would be least likely to result in a high degree of purification?
a. differential centrifugation c. precipitation e. affinity chromatography
b. ion exchange chromatography d. homogenization
28. Which technique would be used to detect the differences in conformation seen in DNAs placed in different chemical environments?
a. X-ray diffraction d. isoelectric focussing
b. SDS - polyacrylamide gel electrophoresis e. DEAE- cellulose chromatography
c. spectrophotometry
29. The effect of ______on eukaryotic cell membranes is to abolish transition temperature.
a. phospholipids b. cholesterol c. gangliosides d. lipid-anchored proteins e. a and b
30. ______are specialized proteins that provide an environment in which proteins that have denatured can renature without interference.
a. Foldases b. Chaperonins c. Molecular chaperones d. Ubiquitins e. b and c
31. Red blood cells with a surface area of ______are lysed and the lipids of their membranes are totally extracted. These lipids are then spread over the surface of a water tank and the surface area covered is found to be 450 µ2.
a. 90 µ2 b. 45 µ2 c. 150 µ2 d. 225 µ2 e. 900 µ2
32. Artificial membranes ______.
a. do not reseal spontaneously if pierced d. b and c
b. possess many properties in common with natural membranes e. a, b and c
c. lack some properties that natural membranes have
33. Which of the following membrane components is amphipathic at least to a small degree?
a. cholesterol b. gangliosides c. transmembrane proteins d. phospholipids e. all of the above
34. Which of the properties below favor the passage of a molecule through a cell membrane?
a. large MW b. hydrophobic c. b and d d. high negative charge e. hydrophilic
35. Which of the following molecules would pass least easily through a lipid bilayer?
a. water b. carbon dioxide c. oxygen d. sodium chloride e. a, b and c
36. Which one of the following molecules will elute last from a gel filtration column? (Assume that all amino acids have the same molecular weight.)
a. a globular protein composed of 187 amino acids d. a globular protein with 165 amino acids
b. a very low molecular weight dye e. a protein consisting of 120 amino acids
c. a cigar-shaped protein of 188 amino acids
37. Which of the techniques below might be used to effect a rapid purification and would be based on the solubility of the molecule to be purified?
a. sucrose density centrifugation d. selective precipitation
b. sodium hydroxide precipitation e. c and d
c. ammonium sulfate precipitation
38. Which technique below is best for determining the precise quantity of radioactive isotope located in a specimen?
a. c and d c. liquid scintillation counting e. ultracentrifugation
b. atomic force microscopy d. autoradiography
39. Which technique below depends on the ability of a protein like a hormone receptor to bind to a specific molecule like the hormone it normally binds?
a. DEAE-cellulose chromatography c. gel filtration e. homogenization
b. selective precipitation d. affinity chromatography
40. One of the most striking features of membranes is exhibited by the distribution of membrane polysaccharides. This property is called ______.
a. asymmetry b. diffusion c. exocytosis d. asynchrony e. effilosis
41. Which technique combines the effects of isoelectric focusing and SDS-PAGE to purify proteins?
a. ion exchange chromatography d. autoradiography
b. three-dimensional gel electrophoresis e. two-dimensional gel electrophoresis
c. spectrophotometry
42. The b-pleated sheet is stabilized by ______.
a. H bonds between polar amino acid R groups
b. covalent bonds
c. H bonds between amide (peptide) linkages oriented parallel to the molecule's axis
d. acidobasic combinations
e. H bonds between amide linkages, oriented perpendicular to the molecule's axis
43. A protein that can be washed off of a cellular membrane by a moderate concentration of a salt solution is called a(n) ______protein.
a. transmembrane b. lipid-anchored c. a and b d. peripheral e. b and d
44. During the summer, some organisms adjust the fluidity of their membranes by ______.
a. increasing phospholipid tail length d. decreasing phospholipid tail length
b. increasing tail unsaturation e. increasing tail saturation
c. a and e
45. What is the minimum number of consecutive helix-forming and/or helix-indifferent amino acids required to form an a-helix?
a. 10 b. 14 c. 3 d. 7 e. 24.5
46. What bonds may be involved in holding together tertiary structure in proteins?
a. peptide bonds b. ionic bonds c. H bonds d. disulfide linkages e. b, c and d
47. What is the highest level of structure exhibited by a protein consisting of one subunit?
a. primary b. secondary c. tertiary d. quaternary e. pentary
48. What property of a b-pleated sheet region of a protein derives from the extended arrangement of its backbone?
a. strength b. flexibility c. extensibility d. a and b e. hardness
II. Short Answer. Please be as brief as possible.
1. What is the highest level of structure exhibited by a protein having more than one subunit? (1 point)
2. If you are attempting to isolate mitochondria from liver tissue, what is the first step in the procedure? (1 point)
Before starting this procedure, why would you place the liver tissue in a cold, isotonic solution? (2 points)
BONUS QUESTIONS - SHORT ANSWER
1. JEOPARDY BONUS QUESTION (Your answer must be in the form of a question.) Subsequent answers need not be in the form of a question. (1 point)