1. 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

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 3

4. When tryptophan (an amino acid) is present in the external medium, the bacterium brings in the tryptophan and does not need to make this amino acid. Which of the following 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 4

5. When tryptophan (an amino acid) is present in the external medium, the bacterium brings in the tryptophan and does not need to make this amino acid. Which of the following 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. 5

6. Each of a group of bacterial cells has a mutation in its lac operon
Each of a group of bacterial cells has a mutation in its lac operon. Which of the following 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
Figure 18.4 6

7. Each of a group of bacterial cells has a mutation in its lac operon
Each of a group of bacterial cells has a mutation in its lac operon. Which of the following 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) 7

8. Which element(s) from the following list constitute(s) a bacterial operon?
repressor gene
promoter
inducer
repressor protein
all of the above
Answer: B 8

9. Which element(s) from the following list constitute(s) a bacterial operon?
repressor gene
promoter
inducer
repressor protein
all of the above 9

10. Which of the following statements about specific transcription factors is false?
The binding of specific transcription factors to the control elements of enhancers influences the rate of gene expression.
Specific transcription factors include activators and repressors.
MyoD is one.
Some act indirectly by affecting chromatin structure.
Interaction of specific transcription factors and RNA polymerase II with a promoter leads to a low rate of initiation and production of a few RNA transcripts.
Answer: E 10

11. Which of the following statements about specific transcription factors is false?
The binding of specific transcription factors to the control elements of enhancers influences the rate of gene expression.
Specific transcription factors include activators and repressors.
MyoD is one.
Some act indirectly by affecting chromatin structure.
Interaction of specific transcription factors and RNA polymerase II with a promoter leads to a low rate of initiation and production of a few RNA transcripts. 11

12. Approximately what proportion of the DNA in the human genome codes for proteins or functional RNA?
83%
46%
32%
13%
1.5%
Answer: E
Concept 18.3 12

13. Approximately what proportion of the DNA in the human genome codes for proteins or functional RNA?
83%
46%
32%
13%
1.5% 13

14. 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 14

15. 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 15

16. RNA is cut up into small 22-nucleotide fragments to regulate another “target” mRNA. Which of the following is/are true?
The target mRNA is degraded, and its protein is not made.
The RNA fragments enhance protein synthesis by the mRNA.
The RNA fragments bind the ribosome to enhance use of the mRNA and protein synthesis.
The target mRNA is blocked from being used in translation.
The RNA fragments act on the ribosome to shut down translation of all mRNAs.
Answer: A or D
Figure 18.14 16

17. RNA is cut up into small 22-nucleotide fragments to regulate another “target” mRNA. Which of the following is/are true?
The target mRNA is degraded, and its protein is not made.
The RNA fragments enhance protein synthesis by the mRNA.
The RNA fragments bind the ribosome to enhance use of the mRNA and protein synthesis.
The target mRNA is blocked from being used in translation.
The RNA fragments act on the ribosome to shut down translation of all mRNAs. 17

18. Even though the two cells have numerous transcription factors and many are present in both cells, the lens cell makes the crystallin protein (not albumin), whereas the liver cell makes albumin (not crystallin). Which of the following explains this cell specificity?
Specific transcription factors made in the cell determine which genes are expressed.
At fertilization, specific cells are destined for certain functions.
The activators needed for expression of the crystallin gene are present in all cells.
The promoters are different for the different genes.
Answer: A
See Figure 18.11, although different combinations of transcription factors are present. 18

19. Even though the two cells have numerous transcription factors and many are present in both cells, the lens cell makes the crystallin protein (not albumin), whereas the liver cell makes albumin (not crystallin). Which of the following explains this cell specificity?
Specific transcription factors made in the cell determine which genes are expressed.
At fertilization, specific cells are destined for certain functions.
The activators needed for expression of the crystallin gene are present in all cells.
The promoters are different for the different genes.
Answer: A
See Figure 18.11, although different combinations of transcription factors are present. 19

20. Differential gene expression (different genes turned on in different cells) leads to different tissues developing in the embryo. Which of the following is not a cause of differential gene expression?
cytoplasmic determinants
induction
the environment around a particular cell
corepressor proteins
Answer: (1) Cytoplasmic determinants. Molecules that are localized within the zygote get put into different cells during cleavage of the embryo and regulate transcription, mRNA usage, or protein activity to cause differentiation of the embryonic cell. (2) Induction. A hormone (or inducer, signaling molecule) will be released by one cell of the embryo and bind to another cell to induce changes in the other cell.

21. Differential gene expression (different genes turned on in different cells) leads to different tissues developing in the embryo. Which of the following is not a cause of differential gene expression?
cytoplasmic determinants
induction
the environment around a particular cell
corepressor proteins
Answer: (1) Cytoplasmic determinants. Molecules that are localized within the zygote get put into different cells during cleavage of the embryo and regulate transcription, mRNA usage, or protein activity to cause differentiation of the embryonic cell. (2) Induction. A hormone (or inducer, signaling molecule) will be released by one cell of the embryo and bind to another cell to induce changes in the other cell.

22. Initially, cytoplasmic determinants are localized in one part of a zygote and could be which of the following? (Choose more than one answer.)
gene
mRNA
transcription factor
ribosome
myoblast
Answer: B, C 22

23. Initially, cytoplasmic determinants are localized in one part of a zygote and could be which of the following? (Choose more than one answer.)
gene
mRNA
transcription factor
ribosome
myoblast 23

24. Scientists showed that bicoid mRNA, and then its Bicoid protein, is normally found in highest concentrations in the fly’s anterior. What would happen if Bicoid were injected at the posterior end?
Anterior structures would form at both ends.
Posterior structures would form at both ends.
The embryo would have no dorsal-ventral axis.
Bicoid mRNA wouldn’t be translated into protein.
Answer: A. Figure Anterior structures would form at both ends. 24

25. Scientists showed that bicoid mRNA, and then its Bicoid protein, is normally found in highest concentrations in the fly’s anterior. What would happen if Bicoid were injected at the posterior end?
Anterior structures would form at both ends.
Posterior structures would form at both ends.
The embryo would have no dorsal-ventral axis.
Bicoid mRNA wouldn’t be translated into protein.
Answer: A. Figure Anterior structures would form at both ends. 25

26. Mutations in _______ genes caused the development of legs in the place of antennae.
homeotic
embryonic lethal
myoD
Ras
wild-type
Wild type
Eye
Mutant
Answer: A. homeotic Figure 18.20 26

27. Mutations in _______ genes caused the development of legs in the place of antennae.
homeotic
embryonic lethal
myoD
Ras
wild-type
Wild type
Eye
Mutant
Answer: A. homeotic Figure 18.20 27

28. The shape of an organ, the number of brain cells in an embryonic brain, the removal of mutated cells, and the webbing cells between the toes of a human embryo are all regulated by which of the following?
certain cells becoming much larger
certain cells shrinking
certain cells dying
formation of embryonic cells
concentration of Bicoid protein
Answer: C 28

29. The shape of an organ, the number of brain cells in an embryonic brain, the removal of mutated cells, and the webbing cells between the toes of a human embryo are all regulated by which of the following?
certain cells becoming much larger
certain cells shrinking
certain cells dying
formation of embryonic cells
concentration of Bicoid protein
Answer: C 29

30. Which of the following would not typically cause a proto-oncogene to become an oncogene?
gene suppression
translocation
amplification
point mutation
retroviral activation
Answer: A 30

31. Which of the following would not typically cause a proto-oncogene to become an oncogene?
gene suppression
translocation
amplification
point mutation
retroviral activation 31

32. Which of the following statements about the APC gene is false?
It is a tumor-suppressor gene.
It is mutated in 60% of colorectal cancers.
It regulates cell migration and adhesion.
It may be deleted in colon cancer.
Mutations in one allele are enough to lose the gene’s function.
Answer: E. Figure 18.26 32

33. Which of the following statements about the APC gene is false?
It is a tumor-suppressor gene.
It is mutated in 60% of colorectal cancers.
It regulates cell migration and adhesion.
It may be deleted in colon cancer.
Mutations in one allele are enough to lose the gene’s function.
Answer: E. Figure 18.26 33

34. Scientific Skills Exercise
The diagrams on the next slide show an intact DNA sequence (top) and three experimental DNA sequences. A red X indicates the possible control element (1, 2, or 3) that was deleted in each experimental DNA sequence. The area between the slashes represents the approximately 8 kilobases of DNA located between the promoter and the enhancer region. The horizontal bar graph shows the amount of reporter gene mRNA that was present in each cell culture after 48 hours relative to the amount that was in the culture containing the intact enhancer region (top bar = 100%).

36. What was the independent variable in this experiment?
the length of time that the cells were incubated
the relative level of reporter gene mRNA
the distance between the promoter and the enhancer
the possible control element that was deleted
Answer: D

37. What was the independent variable in this experiment?
the length of time that the cells were incubated
the relative level of reporter gene mRNA
the distance between the promoter and the enhancer
the possible control element that was deleted

38. What was the dependent variable in this experiment?
the length of time that the cells were incubated
how many of the artificial DNA molecules were taken up by the cells
the relative level of reporter gene mRNA
the distance between the promoter and the enhancer
Answer: C

39. What was the dependent variable in this experiment?
the length of time that the cells were incubated
how many of the artificial DNA molecules were taken up by the cells
the relative level of reporter gene mRNA
the distance between the promoter and the enhancer
Answer: C

40. What was the control treatment in this experiment?
the reporter gene
the construct that had no DNA deleted from the enhancer
the temperature, pH, and salt concentration of the incubation medium
the construct that resulted in the lowest amount of reporter mRNA
Answer: B

41. What was the control treatment in this experiment?
the reporter gene
the construct that had no DNA deleted from the enhancer
the temperature, pH, and salt concentration of the incubation medium
the construct that resulted in the lowest amount of reporter mRNA

42. Do the data suggest that any of these possible control elements are actual control elements?
Only control elements 1 and 2 appear to be control elements.
Only control element 3 appears to be a control element.
All three appear to be control elements.
None of the possible control elements appear to be actual control elements.
Answer: C

43. Do the data suggest that any of these possible control elements are actual control elements?
Only control elements 1 and 2 appear to be control elements.
Only control element 3 appears to be a control element.
All three appear to be control elements.
None of the possible control elements appear to be actual control elements.
Answer: C

44. Did deletion of any of the possible control elements cause a reduction in reporter gene expression? How can you tell?
Deletion of element 3 caused a reduction in reporter gene expression; that construct resulted in less than 50% of the control level of mRNA.
Deletion of elements 2 and 3 caused a reduction in reporter gene expression; those constructs resulted in less than the highest level of mRNA.
None of the deletions caused a reduction in reporter gene expression; all of them still resulted in reporter mRNA being made.
Answer: A

45. Did deletion of any of the possible control elements cause a reduction in reporter gene expression? How can you tell?
Deletion of element 3 caused a reduction in reporter gene expression; that construct resulted in less than 50% of the control level of mRNA.
Deletion of elements 2 and 3 caused a reduction in reporter gene expression; those constructs resulted in less than the highest level of mRNA.
None of the deletions caused a reduction in reporter gene expression; all of them still resulted in reporter mRNA being made.

46. If deletion of a control element causes a reduction in gene expression, what must be the normal role of that control element?
To repress gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression decreases.
To activate gene expression; without the control element, activators are not able to bind to the enhancer, and the level of gene expression decreases.
To repress gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression increases.
To activate gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression increases.
Answer: B

47. If deletion of a control element causes a reduction in gene expression, what must be the normal role of that control element?
To repress gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression decreases.
To activate gene expression; without the control element, activators are not able to bind to the enhancer, and the level of gene expression decreases.
To repress gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression increases.
To activate gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression increases.

48. Did deletion of any of the possible control elements cause an increase in reporter gene expression? How can you tell?
Deletion of control element 1 or 2 caused an increase in reporter gene expression; both constructs resulted in over 100% of the control level of mRNA.
Deletion of control element 1 caused an increase in reporter gene expression; that construct resulted in the highest level of mRNA.
Deletion of control element 3 caused an increase in reporter gene expression; that construct resulted in less reporter mRNA than the control.
All of the deletions caused an increase in reporter gene expression; all of them still resulted in reporter mRNA being made.
Answer: A

49. Did deletion of any of the possible control elements cause an increase in reporter gene expression? How can you tell?
Deletion of control element 1 or 2 caused an increase in reporter gene expression; both constructs resulted in over 100% of the control level of mRNA.
Deletion of control element 1 caused an increase in reporter gene expression; that construct resulted in the highest level of mRNA.
Deletion of control element 3 caused an increase in reporter gene expression; that construct resulted in less reporter mRNA than the control.
All of the deletions caused an increase in reporter gene expression; all of them still resulted in reporter mRNA being made.

50. If deletion of a control element causes an increase in gene expression, what must be the normal role of that control element?
To activate gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression increases.
To repress gene expression; without the control element, activators are not able to bind to the enhancer, and the level of gene expression decreases.
To repress gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression increases.
To activate gene expression; without the control element, activators are not able to bind to the enhancer, and the level of gene expression decreases.
Answer: C

51. If deletion of a control element causes an increase in gene expression, what must be the normal role of that control element?
To activate gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression increases.
To repress gene expression; without the control element, activators are not able to bind to the enhancer, and the level of gene expression decreases.
To repress gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression increases.
To activate gene expression; without the control element, activators are not able to bind to the enhancer, and the level of gene expression decreases.