Molecular Genetics 447:482
Exam 2, Fall 2000
November 7, 2000
Name
Short Essays
Describe what nonsense suppressors are.
Imagine your working for a biotech company that is focused on commercial production of
vitamins from bacteria. Expression of a single gene (vitZ) causes E. coli to produce large
amounts of vitamin Z. The goal for the company is to “turn-on” production of vitamin Z at the
optimum point in the production process and your job is to create the necessary E. coli strain.
Explain your genetic engineering strategy to achieve the company’s goal?
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Molecular Genetics 447:482
Exam 2, Fall 2000
November 7, 2000
1. Which gene component is found at the very end of an operon?
A. RNA polymerase binding site
B. Translational termination site
C. Transcriptional termination site
D. Ribosome binding site
E. The coding sequence
2. Why are there 3 operator sites to which lacI binds?
A. Only O1 is functional in repression, the others are cryptic sites
B. LacI binding is most stable when O1 and a O2 or O3 are bound at once
C. LacI binding is most stable when all 3 operators are bound at once
D. Redundancy, just in case one operator is mutated there are other functional copies
E. Binding to one operator represses translation while another represses transcription
3. Which gene component is located upstream of the transcriptional initiation site?
A. RNA polymerase binding site
B. Translational termination site
C. Transcriptional termination site
D. Ribosome binding site
E. The coding sequence
4. Which gene component is likely to be found in the intergenic region of an operon?
A. RNA polymerase binding site
B. Translational termination site
C. Transcriptional termination site
D. Ribosome binding site
E. The coding sequence
5. What is a helix-turn-helix motif?
A. Domain responsible for association of subunits in some transcription factors.
B. DNA operator site where a transcription factor binds
C. DNA binding domain found in some DNA binding proteins
D. DNA region surrounding the transcription initiation site
E. Domain of LacI that binds the inducer
6. What is the function of the N protein?
A. Transcription termination
B. Transcription antitermination
C. Translation termination
D. Translational antitermination
E. None of the above
7. How does Rho function?
A. By preventing intramolecular base pairing within RNA
B. By binding to the terminator
C. By phosphorylating RNA polymerase
D. By causing the unwinding of the RNA-DNA hybrid
E. By dissociating ribosomal subunits
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Molecular Genetics 447:482
Exam 2, Fall 2000
November 7, 2000
8. Which RNA polymerase subunit binds the –35 promoter sequence?
A. (alpha)
B.  (beta)
C. ' (beta prime)
D.  (sigma)
E. NusA
9. Which of the following compounds is an adenylate cyclase null mutant unable to produce?
A. Lactose
B. cAMP
C. Glucose
D. pppGpp
E. ATP
10. Which of the following describes the "Stringent Response"?
A. Recombination is induced when DNA damaged
B. Expression of some genes is induced when bacteria are starved for an essential nutrient
C. The ability to undergo autolysis when nutrients are unavailable
D. Expression of some genes is repressed when bacteria are starved for an essential nutrient
E. Expression of some genes is induced in response to alterations in osmotic pressure
11. At what position in an operon would an attenuator function most effectively?
A. 5' of the transcriptional start site
B. 3' of the last gene in the operon
C. Between the transcriptional start site and the translational initiation site of the first gene
D. Between the -10 and -35 sequences
E. In the coding region of any gene in the operon
12. What is antisense RNA?
A. RNA that makes up the structural component of ribosomes
B. mRNA transcribed from a gene with a nonsense mutation
C. RNA transcript base paired with DNA during transcription elongation
D. RNA transcript that is complementary to an mRNA
E. The DNA strand complementary to the template strand
13. Why are DNA operator sites a palindrome?
A. They interact with a protein that is a symmetrical dimmer
B. They serve as the recognition site for a restriction endonuclease
C. RNA polymerase initiates transcription at these sites
D. Palindromes make excellent protein binding sites
E. So they can form a stem loop
14. Which of the following enzymes is necessary for the technique of "DNA footprinting”?
A. DNA polymerase
B. RNA polymerase
C. DNA gyrase
D. DNAse I
E. A restriction endonuclease
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Molecular Genetics 447:482
Exam 2, Fall 2000
November 7, 2000
15. What do aminoacyl tRNA synthetases do?
A. Transcribe tRNA genes
B. Modify the nitrogenous bases of tRNAs
C. Link amino acids with tRNAs
D. Synthesize amino acids
E. It is a factor required for translational initiation
16. What does puromycin do?
A. Inhibits transcription
B. Inhibits translation
C. Inhibits replication
D. Induces transcription
E. It is one of the “magic spots”
17. Which of the elongation factors is the target of diphtheria toxin?
A. EF-Tu
B. EF-G
C. eEF1
D. eEF2
E. RF1
18. Which gene encodes the protein that is first bind to the E. coli chromosomal origin?
A. dnaA
B. dnaB
C. dnaC
D. dnaG
E. dnaT
19. Which gene encodes an RNA polymerase?
A. dnaA
B. dnaB
C. dnaC
D. dnaG
E. dnaT
20. What is oriC?
A. The replication origin of the E. coli chromosome
B. The replication terminator of the E. coli chromosome
C. A trans factor required for initiation of replication at the chromosome origin.
D. The gene encoding a factor required for termination of replication.
E. A transcriptional regulator of genes required during oxidative stress.
Mini-Matching (match the protein with the description of its function)
21. RelA
A. Transcriptional repressor requiring a co-repressor
22. LacI
B. Transcriptional repressor requiring an inducer
23. TrpR
C. Transcriptional activator requiring an inducer
24. CAP
D. RNA polymerase subunit that is the target of transactivation
E. Ribosome-associated protein that regulates transcription
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Molecular Genetics 447:482
Exam 2, Fall 2000
November 7, 2000
Mini-Matching (match the lacI mutation with the description of its phenotype)
25. lacI-S
A. Uninducible Lac genes, dominant over wild-type lacI
-q
26. lacI
B. Uninducible Lac genes, recessive to wild-type lacI
27. lacI-d
C. Constitutively expresses Lac genes, dominant over lacI wild-type
28. lacI+
D. Constitutively expressed Lac genes, recessive to wild-type lacI
E. Higher concentrations of inducer are required to induce the Lac operon
Mini-Matching (match the E. coli mutation with the description of its phenotype)
29. sigma32 gene (rpoH-)
A. Unable to grow on tryptophan as a carbon source
ts
30. rpoB
B. Constitutively produces porins in the outer membrane
31. ompRC. Cells die at high temperature
32. nusA
D. All gene expression is blocked at a non-permissive temperature
E. Unable to support growth of lambda phage
True (A) or False (B)
33. DNA loop formation is involved in expression of the Lac operon
34. RNA polymerase core enzyme can initiate transcription at promoters
35. DNA polymarase III core enzyme is unable to initiate replication on its own
36. DNA polymerase I consists of two separate proteins called Klenow and 3’ to 5’ exonuclease
37. Factor-independent transcriptional termination sites do not serve in regulation of gene
expression
38. Transcriptional initiation at the Lac operon requires the sigma70 RNA polymerase
holoenzyme
39. The Trp attenuator causes down-regulation of the Trp operon when tryptophan is limiting
40. A specific termination tRNA is required for translational termination at the UGA codon
41. BglG is a transcriptional antitermination factor
42. Autogenous control means that an enzyme’s activity is regulated by its catalytic product
43. micF is an antisense RNA involved in regulation of the bgl operon
44. The LacI protein is composed of 4 identical subunits
45. The leading strand in DNA replication is synthesized discontinuously
46. Two DNA polymerase core enzymes are held together by the Tau subunits
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Molecular Genetics 447:482
Exam 2, Fall 2000
November 7, 2000
Answer Key
1. C, 2. B, 3. A, 4. D, 5. C, 6. B, 7. D, 8. D, 9. B, 10. D, 11. C, 12. D, 13. A, 14. D, 15. C
16. B, 17. D, 18. A, 19. D, 20. A, 21. E, 22. B, 23. A, 24. C, 25. D, 26. E, 27. C
28. , DISQUALIFIED, 29. C, 30. D, 31. B, 32. E, 33. A, 34. B, 35. A, 36. B, 37. B, 38. A
39. B, 40. B, 41. A, 42. B, 43. B, 44. A, 45. B, 46. A
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