Biology 263 Cell Biology
Joel Piperberg March 18, 2011
Second Exam Page # 1
Name ______
I. Multiple Choice. Fill in the circle on the test form corresponding to the correct answer.
1. 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
2. Which technique below depends on the ability of a protein like a hormone receptor to bind to its specific hormone?
a. DEAE-cellulose chromatography c. gel filtration e. homogenization
b. selective precipitation d. affinity chromatography
3. Which technique combines the methods 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
4. 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
5. 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
6. 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.
7. What kind of polypeptide structure involves interaction within the same chains in the form of H bonds parallel to the axis of the molecule?
a. primary b. secondary c. tertiary d. a-helix e. b and d
8. 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
9. What bonds are involved in holding together tertiary structure in proteins?
a. glycosidic linkages c. van der Waals interactions e. b, c and d
b. hydrophobic interactions d. ionic bonds
10. The final protein conformation (the 3-D shape) is determined by ______.
a. the interaction between the R groups within the protein's backbone
b. interaction between phospholipid R groups
c. the interaction between adjacent or nearly adjacent regions of the nucleic acid backbone
d. the primary structure
e. all of the above
11. Which property below is typical of a-helical structure?
a. a high degree of extensibility b. strength c. flexibility d. rigidity e. b and c
12. Nucleation is most closely associated with which phenomenon below?
a. renaturation b. protein folding c. transcription d. translation e. a and b
13. Which technique could be used for molecular weight determinations in proteins under all circumstances?
a. gel filtration c. carboxymethyl (CM) cellulose chromatography e. SDS-PAGE
b. isoelectric focusing d. a and e
14. 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
15. Some transport proteins convey molecules through a membrane and up a concentration gradient by binding to the molecules. These transport proteins have some of the properties of enzymes. What type of transport is coordinated by these proteins?
a. active transport c. passive diffusion e. a and d
b. facilitated diffusion d. carrier-mediated transport
16. Some channel proteins will allow things to pass through at all times. Others allow molecules or ions to pass through only at certain times. Such a transport protein is called a ______.
a. rated channel b. gated channel c. gated carrier d. b and e e. integral protein
17. Ouabain is a very specific inhibitor of the active transport of sodium ions out of the cell and is therefore a valuable tool in studies of membrane transport mechanisms. Which of the following processes in your own body would you expect to be sensitive to inhibition by ouabain?
a. passive transport of glucose into a muscle cell
b. active transport of dietary phenylalanine across the intestinal mucosa
c. uptake of potassium ions by liver cells
d. active uptake of lactose by the bacteria living in your intestine
e. none of the above
18. ______is a small, hydrophobic molecule that dissolves in a membrane and increases ion permeability sometimes with disastrous results for a cell.
a. Penicillin b. Valinomycin c. An ionoclast d. a and c e. Stillomycin
19. A type of membrane transport that brings molecules into the cell randomly is ______.
a. receptor-mediated endocytosis c. facilitated diffusion e. fluid-phase endocytosis
b. a and e d. a, c and e
20. You are studying the transport of two molecules through the cell membrane. Their transport appears to be linked and both enter the cell together. If the transport of one is halted so is the other. If an inhibitor of ATP synthesis is added to the cells containing the transport molecule, there is a cessation of transport of the two molecules. What words best describe the transport molecule?
a. active antiport b. active symport c. passive symport d. passive antiport e. active uniport
21. 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
22. 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
23. At times, proteins will denature. When they do, they will refold with the aid of special proteins that provide a "chamber" within which the denatured proteins can refold without interference from the surrounding cytoplasm. What are these proteins called?
a. ubiquitins b. chaperonins c. molecular chaperones d. b and c e. refoldases
24. Active transport is characterized by ______.
a. transport against a concentration gradient d. a and c
b. transport down a concentration gradient e. b and c
c. the requirement for energy often in the form of ATP hydrolysis
25. What is an electrochemical gradient?
a. a gradient in charge and molecular weight d. a gradient in molecular weight & concentration
b. a gradient in molecular weight alone e. a gradient in charge and concentration
c. a gradient in concentration
26. The process by which molecules are secreted from a cell is called ______.
a. exocytosis b. endocytosis c. phagocytosis d. sarcosis e. meiosis
27. A membrane transport molecule that transports two molecules in the same direction can be called a(n) ______.
a. uniport b. antiport c. symport d. cotransport system e. c and d
28. The protein that aids in the formation of the vesicles during receptor-mediated endocytosis is ______.
a. classrin b. ankyrin c. trifskelturin d. clathrin e. glycophorin
29. The Na+ - K+ pump makes the cell interior ___ because it pumps ____ Na+ out for every ____ K+ pumped in.
a. neutral; 3; 3 b. negative; 2; 3 c. positive; 2; 3 d. negative; 3; 2 e. positive; 3; 2
30. 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
31. You are studying a membrane transport molecule. You have discovered that it transports Cl- and glucose. You have prepared inside-out and right-side out vesicles. If both of the above substances are found on the same side of either type of vesicle transport is not seen to occur. If, on the other hand, glucose is placed inside and Cl- is placed outside the inside-out vesicles, transport takes place. Which of the following statements about the transport molecule is true?
a. it is an antiport which would work if Cl- were placed inside and glucose were placed outside the right-side-out vesicles
b. it is a symport that would work if Cl- and glucose were placed outside the right-side-out vesicles
c. it is a symport that would work if Cl- and glucose were placed inside the right-side-out vesicles
d. it is an antiport which would work if Cl- were placed outside and glucose were placed inside the right-side-out vesicles
e. none of the above
32. What might the cellular basis of a disease called familial hypercholesterolemia (an inherited disease in which blood cholesterol levels are very high) be?
a. none of the other answers c. Receptors for LDL bind it too tightly. e. c and d
b. Receptors for HDL do not bind it. d. Receptors for LDL are not made.
33. Some membrane transport proteins allow molecules to leave or enter cells by moving down the concentration gradient by binding to the transport protein. This can occur as long as the molecule to be transported can bind specifically to the transport molecule. Such a molecule is called a(n) _____ protein.
a. channel b. a, c and e c. intermembrane d. a and e e. carrier
34. 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
35. 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 - lysine - histidine - arginine - C d. N - leucine - alanine - glycine - C
b. N - aspartate - glutamate - aspartate - C e. N - aspartate - phenylalanine - histidine - C
c. N - phenylalanine - aspartate - glycine - C
36. 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
37. 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
38. Which molecular component of the lipid bilayer is at least to a small degree amphipathic?
a. extrinsic proteins b. phospholipids c. cerebrosides d. b, c and e e. gangliosides
39. A protein you wish to study is located in the mitochondria of rat liver cells and is readily extractable from partially purified peroxisomes. 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
40. 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
41. 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
42. 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
43. 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
44. 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
45. 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 900 µ2.
a. 112.5 µ2 b. 1800 µ2 c. 450 µ2 d. 225 µ2 e. 900 µ2
II. Short Answer. Please be as brief as possible.
1. What is the highest level of structure exhibited by a protein having 12 subunits? (1 point)
2. Why was the Unit Membrane Model of membrane structure eventually rejected? (1 point)
3. Briefly name and define the levels of structure in proteins. What types of bonds are instrumental in holding each level of structure together? (8 points)
Level of Structure /Definition
/ Bond(s) InvolvedBONUS QUESTIONS - LECTURE-SHORT ANSWER
1. JEOPARDY BONUS QUESTION (Your answer must be in the form of a question). (2 points)
This "giant" ocean dweller has the largest eyes of any creature.
2. What is responsible for breaking disulfide linkages in proteins being subjected to the type of electrophoresis that allows the direct determination of molecular weight? In that same technique, another reagent denatures the proteins and coats them with negative charges that will cause them to be attracted to the positive electrode. What is the name of that reagent? (2 points)