1. 15
Regulation of Gene Expression

2. What does the operon model attempt to explain?
the coordinated control of gene expression in bacteria
bacterial resistance to antibiotics
how genes move between homologous regions of DNA
the mechanism of viral attachment to a host cell
horizontal transmission of plant viruses
Answer: A.
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3. What does the operon model attempt to explain?
the coordinated control of gene expression in bacteria
bacterial resistance to antibiotics
how genes move between homologous regions of DNA
the mechanism of viral attachment to a host cell
horizontal transmission of plant viruses
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4. When tryptophan (an amino acid) is present in the external medium, the E. coli bacterium brings in the tryptophan and does not need to make this amino acid. Which is true when there is no tryptophan in the medium?
The repressor is active and binds to the operator.
The repressor is inactive, and RNA polymerase moves through the operator.
The operator is bound, and mRNA is made.
Genes are inactive.
The corepressor binds to the repressor.
Answer: B.
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5. When tryptophan (an amino acid) is present in the external medium, the E. coli bacterium brings in the tryptophan and does not need to make this amino acid. Which is true when there is no tryptophan in the medium?
The repressor is active and binds to the operator.
The repressor is inactive, and RNA polymerase moves through the operator.
The operator is bound, and mRNA is made.
Genes are inactive.
The corepressor binds to the repressor.
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6. Each of a group of E. coli bacterial cells has a mutation in its lac operon. Which of these will make it impossible for the cell to metabolize lactose?
mutation in lac (-galactosidase gene)
mutation in lac (cannot bind to operator)
mutation in operator (cannot bind to repressor)
mutation in lac (cannot bind to inducer)
Answer: A. See Figure 15.4.
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7. Each of a group of E. coli bacterial cells has a mutation in its lac operon. Which of these will make it impossible for the cell to metabolize lactose?
mutation in lac (-galactosidase gene)
mutation in lac (cannot bind to operator)
mutation in operator (cannot bind to repressor)
mutation in lac (cannot bind to inducer)
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8. A specific gene is known to code for three different but related proteins. This could be due to which of the following?
premature mRNA degradation
alternative RNA splicing
use of different enhancers
protein degradation
differential transport
Answer: B.
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9. A specific gene is known to code for three different but related proteins. This could be due to which of the following?
premature mRNA degradation
alternative RNA splicing
use of different enhancers
protein degradation
differential transport
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10. Which methods would determine which genes are turned on in a certain cell in an organism? (Choose more than one answer.)
Use RT-PCR to identify what mRNAs are present.
Use RT-PCR to measure what proteins are present.
Use a radioactive probe that binds only to certain mRNAs.
Use a fluorescent probe that records DNA replication.
Use a fluorescent probe that binds to only certain mRNAs.
Answer: A, C, E.
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11. Which methods would determine which genes are turned on in a certain cell in an organism? (Choose more than one answer.)
Use RT-PCR to identify what mRNAs are present.
Use RT-PCR to measure what proteins are present.
Use a radioactive probe that binds only to certain mRNAs.
Use a fluorescent probe that records DNA replication.
Use a fluorescent probe that binds to only certain mRNAs.
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12. Pair the following terms by their physical binding with each other: promoter, operator, RNA polymerase, repressor protein.
RNA polymerase with repressor protein, promoter with operator
RNA polymerase with promoter; repressor protein with operator
RNA polymerase with operator; repressor protein with promoter
Answer: B.
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13. Pair the following terms by their physical binding with each other: promoter, operator, RNA polymerase, repressor protein.
RNA polymerase with repressor protein, promoter with operator
RNA polymerase with promoter; repressor protein with operator
RNA polymerase with operator; repressor protein with promoter
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14. Imagine an E. coli cell with a mutation that renders its trp repressor protein completely inactive. Which of the following would be true of that cell?
It synthesizes tryptophan only when tryptophan is absent.
It never synthesizes tryptophan.
It always synthesizes tryptophan.
It synthesizes tryptophan only when tryptophan is present.
Answer: C. Without an active repressor, the operon would always be active.
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15. Imagine an E. coli cell with a mutation that renders its trp repressor protein completely inactive. Which of the following would be true of that cell?
It synthesizes tryptophan only when tryptophan is absent.
It never synthesizes tryptophan.
It always synthesizes tryptophan.
It synthesizes tryptophan only when tryptophan is present.
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16. In normal E. coli cells, under which of the following conditions is the lac operon “ON”?
glucose present, lactose present
glucose absent, lactose absent
glucose present, lactose absent
glucose absent, lactose present
Answer: D. This questions highlights the dual control of the lac operon.
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17. In normal E. coli cells, under which of the following conditions is the lac operon “ON”?
glucose present, lactose present
glucose absent, lactose absent
glucose present, lactose absent
glucose absent, lactose present
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18. In normal E. coli cells, in which the lac operon is “ON,” which combination of CAP and lac repressor proteins is bound to the lac operon?
both cap and lac repressor
neither cap nor lac repressor
only cap
only lac repressor
Answer: C. This questions highlights the dual control of the lac operon.
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19. In normal E. coli cells, in which the lac operon is “ON,” which combination of CAP and lac repressor proteins is bound to the lac operon?
both cap and lac repressor
neither cap nor lac repressor
only cap
only lac repressor
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20. Imagine an E. coli cell in which the lac operator has a mutation that renders it unable to bind the lac repressor. When would its lac operon be “ON”?
always
never
when glucose levels are low
only when glucose levels are low and lactose levels are high
Answer: C. This questions highlights the dual control of the lac operon. The operon will not respond to lactose levels, but will still respond to glucose levels via CAP.
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21. Imagine an E. coli cell in which the lac operator has a mutation that renders it unable to bind the lac repressor. When would its lac operon be “ON”?
always
never
when glucose levels are low
only when glucose levels are low and lactose levels are high
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22. Histone de-acetylases (HDACs) are enzymes that remove acetyl groups from histone proteins. With regard to their effects on transcription, HDACs should do which of the following?
activate transcription by opening chromatin
activate transcription by condensing chromatin
repress transcription by opening chromatin
repress transcription by condensing chromatin
Answer: D.
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23. Histone de-acetylases (HDACs) are enzymes that remove acetyl groups from histone proteins. With regard to their effects on transcription, HDACs should do which of the following?
activate transcription by opening chromatin
activate transcription by condensing chromatin
repress transcription by opening chromatin
repress transcription by condensing chromatin
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24. Why is a myosin gene transcriptionally expressed in muscle cells, but not in neurons?
Neurons lack an enhancer in the myosin gene.
Neurons lack the myosin gene.
Muscle cells have an extra enhancer in the myosin gene.
Muscle cells express an activator protein that binds the myosin enhancer.
Answer: D. The DNA should be the same in all cells. The presence of specific proteins can be different between cell types.
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25. Why is a myosin gene transcriptionally expressed in muscle cells, but not in neurons?
Neurons lack an enhancer in the myosin gene.
Neurons lack the myosin gene.
Muscle cells have an extra enhancer in the myosin gene.
Muscle cells express an activator protein that binds the myosin enhancer.
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26. A eukaryotic gene has a pre-mRNA with five exons (1, 2, 3, 4, 5)
A eukaryotic gene has a pre-mRNA with five exons (1, 2, 3, 4, 5). Which of the following arrangements of exons is not possible in a mature mRNA due to alternative splicing?
1, 2, 5
1, 3, 4, 5
1, 3, 2, 4, 5
1, 3, 3, 5
Answer: C, D. Splicing preserves the relative order of exons. Exons can be skipped, but not rearranged or duplicated. The system does not allow for repeating exons or changing the 5’ → 3’ order.
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27. A eukaryotic gene has a pre-mRNA with five exons (1, 2, 3, 4, 5)
A eukaryotic gene has a pre-mRNA with five exons (1, 2, 3, 4, 5). Which of the following arrangements of exons is not possible in a mature mRNA due to alternative splicing?
1, 2, 5
1, 3, 4, 5
1, 3, 2, 4, 5
1, 3, 3, 5
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28. A mi-RNA binds with perfect complementarity to a target mRNA of gene X
A mi-RNA binds with perfect complementarity to a target mRNA of gene X. What is/are the outcome(s) for gene X in terms of gene regulation?
less gene X
less pre-mRNA of gene X
less mRNA of gene X
less protein of gene X
Answer: C, D. D follows from C.
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29. A mi-RNA binds with perfect complementarity to a target mRNA of gene X
A mi-RNA binds with perfect complementarity to a target mRNA of gene X. What is/are the outcome(s) for gene X in terms of gene regulation?
less gene X
less pre-mRNA of gene X
less mRNA of gene X
less protein of gene X
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30. A particular oncogene with the partial mRNA sequence of 5ʹ AUG GAU GGG is expressed in certain cancer cells. What partial DNA sequence would be part of an effective probe to determine if this oncogene were being expressed in cells?
5ʹ ATG GAT GGG
5ʹ GGG TAG GTA
5ʹ CCC ATC CAT
5ʹ TAC CTA CCC
Answer: C. A probe must be the reverse complement of the target sequence.
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31. A particular oncogene with the partial mRNA sequence of 5ʹ AUG GAU GGG is expressed in certain cancer cells. What partial DNA sequence would be part of an effective probe to determine if this oncogene were being expressed in cells?
5ʹ ATG GAT GGG
5ʹ GGG TAG GTA
5ʹ CCC ATC CAT
5ʹ TAC CTA CCC
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