Lab 6: Biotechnology Multiple Choice Questions

Transcription

1 Lab 6: Biotechnology Multiple Choice Questions 1. The enzyme that is found in retroviruses and that is required for the synthesis of DNA from RNA is DNA polymerase III RNA polymerase restriction endonuclease reverse transcriptase dehydrogenase (1990 #52) 2. A tobacco plant can be made to express a gene from fireflies, resulting in the emission of light. Which of the following is the basis for this phenomenon? (A.) Chloroplasts can be made to produce light if firefly proteins are injected into plant cells. (B.) Fireflies and tobacco plants share a recent common ancestor. (C.) Fireflies and tobacco plants are infected by the same kinds of bacteria (D.) Transcription and translation are fundamentally similar in both fireflies and tobacco plants. (E.) Most enzymes in fireflies have the same amino acid sequence as the enzymes in tobacco plants. (1999 # 38)

2 Directions: Each group of questions below concerns an experimental or laboratory situation or data. In each case, first study the description of the situation or data. Then choose the one best answer to each question following it and fill in the corresponding oval on the answer sheet. Questions 3-6 A scientist is using an ampicillin-sensitive strain of bacteria that cannot use lactose because it has a nonfunctional gene in the lac operation. She has two plasmids. One contains a functional copy of the affected gene of the lac operon, and the other contains the gene for ampicillin resistance. Using restriction enzymes and DNA ligase, she forms a recombinant plasmid containing both genes. She then adds a high concentration of the plasmid to a tube of the bacteria in a medium for bacterial growth that contains glucose as the only energy source. This tube (+) and a control tube (-) with similar bacteria but no plasmid are both incubated under the appropriate conditions for growth and plasmid uptake. The scientist then spreads a sample of each bacterial culture (+ and -) on each of the three types of plates indicated below. 3. If no new mutations occur, it would be most reasonable to expect bacterial growth on which of the following plates? (1999 #96) 1 and 2 only 3 and 4 only 5 and 6 only 4, 5, and 6 only 1, 2, 3, and 4 only

3 4. The scientist used restriction enzymes for what purpose in the experiment? (1999 #97) To make the plasmid small enough to transform cells To make cuts in the plasmid DNA To make the plasmid enter the cells To enable to fragments of DNA to form covalent bonds To enable the plasmid to recognize the bacterial cells 5. If the scientist had forgotten to use DNA ligase during the preparation of the recombinant plasmid, bacterial growth would most likely have occurred on which of the following? (1999 #98) 1 and 2 only 1 and 4 only 4 and 5 only 1, 2, and 3 only 4, 5, and 6 only 6. If the scientist used the cultures to perform another experiment as shown above, using medium that contained lactose as the only energy source, growth would most likely occur on which of the following plates? (1999 #99) 10 only 7 and 8 only 7 and 9 only 8 and 10 only 9 and 10 only

4 Questions 7-9 refer to an experiment that was performed to separate DNA fragments from four samples radioactively labeled with 32 P. The fragments were separated by gel electrophoresis. The visualized bands are illustrated in the figure below. 7. The electrophoretic separation of the pieces of DNA in each of the four samples was achieved because of differential migration of the DNA fragments in an electric field. This differential migration was caused by the relative amounts of radioactivity in the DNA number of cleavage points per fragment size of each fragment overall positive charge of each fragment solubility of each fragment (1999 # 111) 8. The DNA was labeled with 32 P in order to stimulate DNA replication inhibit the uptake of unlabeled ATP show which fragments included the 5 end and which fragments included the 3 end visualize the fragments speed up the rate of separation by electrophoresis (1999 # 112)

5 9. Which of the following is an additional use of the gel electrophoresis technique? To express a gene To separate proteins in a mixture To ligate DNA fragments To transform E. coli To amplify genes (1999 # 113) Questions A student uses restriction enzymes to cut a DNA molecule into fragments. The digested DNA is loaded into the wells of an agarose gel and the gel is subjected to an electric current. Upon completion of the run, the gel is stained. 10. The rate of migration of the DNA fragments through the agarose gel is determined by the ratio of adenine to cytosine in the fragment presence of hydrogen bonds between base pairs length of time the electrophoresis unit is allowed to operate number of nucleotides in the fragment volume of the starting sample 11. Which of the following is true of the dye used to stain the fragments? It increases the contrast between the agar and the DNA fragments. It must be accounted for when calculating the molecular weight of the fragments. Its charged areas interfere with the migration of the DNA. It is bonded only to the sticky ends of the fragments and can directly determine the sequence of the DNA fragments. It gives a three-dimensional view of the structure of the DNA fragments. 12. The type and density of the gel are important because they influence the rate of migration of the fragments they may cause some DNA molecules to replicate some DNA nucleotides may be lost due to chemical reactions with the gel some DNA molecules may sink to the bottom and not migrate some DNA molecules may cross-link 13. The procedures described can be used to do all of the following EXCEPT isolate and purify certain DNA fragments synthesize novel DNA molecules study the activity of restriction enzymes calculate the size of DNA fragments identify the source of DNA material

6 Questions are based on the following. In the 1940 s, Avery, MacCleod, and McCarty transformed nonencapsulated bacteria into encapsulated forms by growing the nonencapsulated cells in a culture containing an extract made from dead encapsulated cells. The transformed cells produced colonies of encapsulated bacteria. Three different procedures and their results are outlined below. Procedure I: Exact made from dead encapsulated cells added to culture medium. Nonencapsulated bacteria added to culture medium. Results: Both nonencapsulated and encapsulated bacteria grow. Procedure II: Extract made from dead encapsulated cells treated with protein-degrading enzymes before adding exact to culture medium. Nonencapsulated bacteria added to culture medium. Results: Both nonencapsulated and encapsulated bacteria grow. Procedure III: Extract made from dead encapsulated cells treated with DNAse (an enzyme that selectively destroys DNA) before adding extract to culture medium. Nonencapsulated bacteria added to culture medium. Results: Only nonencapsulated bacteria grow. 14. A reasonable conclusion to draw from the results of the experiment is that DNA is the genetic material DNA replication is semiconservative DNA is a double helix DNA is translated into protein Mutation is a change in the genetic material 15. What was the purpose of treating the extract with protein-degrading enzymes in Procedure II? To demonstrate that the transforming factor is an enzyme To demonstrate that the transforming factor is not a protein To destroy nucleic acids in the exact To destroy any capsules in the exact To prevent the extract from being contaminated by nonencapsulated bacteria

7 16. What was the purpose of treating the extract with DNAse in Procedure III? To remove the encapsulated bacteria from the extract To serve as a positive control by demonstrating that a protein in the extract is the transforming factor To serve as a negative control by demonstrating that transformation does not occur without DNA To destroy any enzymes in the extract To destroy any capsules that might be in the extract