Microbiology chapter 14

14. In attenuation regulation of the trp operon, which stem loop forms when tryptophan is readily available to the cell?

A. 3:4

54. The standard or housekeeping sigma factor used most often by E. coli RNA polymerase under normal growth conditions is called sigma ___.

A. 70

34. Which statement best describes the mechanism(s) of posttranslational regulation of gene expression? odification.

A. Allosteric regulation following transcription of mRNA occurs in many biosynthetic pathways.

36. Which of the following is an example of gene regulation at the posttranslational level?

A. Alteration of protein structure

8. ______________ is used to control transcription of some anabolic pathways involved in amino acid biosynthesis.

A. Attenuation

35. Which of the following statements best explains why microbial geneticists initially focused on regulation of gene expression at the transcriptional, rather than the translational, level?

A. By regulating the first step of protein synthesis, cells conserve the greatest amount of energy.

75. In catabolite repression systems of some Gram-positive bacteria, such as Bacillus subtilis, transcription of catabolic operons is regulated by CcpaA (catabolite control protein A) rather than cAMP. Propose a hypothesis to explain the preferential use of glucose in the presence of a second sugar such as sucrose by Bacillus subtilis.

A. CcpaA acts as a repressor of sucrose operon genes in Bacillus subtilis when both sugars are present.

71. Which of the following events occurs initially when Escherichia coli cells are in a gradient of a chemorepellent?

A. CheA autophosphorylates

5. An sRNA is isolated from a bacterial cell. What would you do to determine whether it is a cis-encoded or a trans-encoded sequence?

A. Identify whether or not the sRNA sequence is complementary to the coding strand of mRNA gene target.

28. __________ alter repressor proteins thereby increasing the rate of transcription initiation.

A. Inducers

74. What is the function of cyclic dimeric GMP in bacterial global regulation systems?

A. It acts as a secondary nucleotide messenger.

68. In which situation might methylation of membrane proteins in Escherichia coli initiate a phosphorelay system that evokes clockwise rotation of flagella?

A. Presence of a chemorepellent in the extracellular environment.

38. When does a cell regulate gene expression?

A. Pretranscription through postranslation

58. During sporulation in Bacillus subtilis, inactive precursor forms of new sigma factors are activated at the appropriate time by which mechanism?

A. Proteolysis

20. Serratia marcescens bacteria has a gene that regulates red pigment production by cells. A student inoculates two nutrient agar plates of Serratia and incubates one at 25oC and the other at 37oC. Following incubation, the student observes that colonies on the 25oC plate are red while those on the 37oC plate are nonpigmented. Which of the following statements is a logical conclusion based on these results?

A. Serratia genes for pigment production are induced at certain temperatures.

2. How do translational riboswitches and transcriptional riboswitches differ?

A. Translational riboswitches are mainly observed in Gram-negative bacteria while transcriptional riboswitches are associated with Gram-positive bacteria.

66. Bioluminescence in Vibrio harveyi is due to an alternate sigma factor that prevents from binding to Lux mRNA, thus allowing translation of bioluminescent genes.

A. antisense

70. If flagellar rotation of Escherichia coli cells is , then CheA is .

A. counterclockwise; unphosphorylated

69. If autophosphorylation of CheA protein does not occur, then Escherichia coli cells must be

A. in a gradient of a chemoattractant.

29. When a repressor binds to the operator site on the DNA it normally

A. inhibits the initiation of transcription.

72. In terms of global gene regulation, which of the following molecules is most similar to c-di-GMP and cAMP?

A. ppGpp

12. The terminator versus anti-terminator function of the T box-based riboswitch used by Gram-positive bacteria to regulate amino acid-related genes is determined by

A. the binding of the appropriate uncharged tRNA.

53. The activity of adenyl cyclase is influenced by

A. the phosphotransferase system.

50. If Escherichia coli is cultured in broth containing both glucose and lactose, it

A. uses glucose preferentially until the supply is exhausted, then uses lactose.

22. In terms of transcription regulation, the role of a helix-turn-helix is most similar to that of a(n) .

A. zinc finger

17. Which of the following is not a regulatory mechanism used to control the tryptophan operon in Escherichia coli?

B. Catabolite repression

27. __________ activate repressor proteins, thereby decreasing the synthesis of certain enzymes.

B. Corepressors

51. What term describes a set of genes that is controlled by a common regulatory protein?

B. Regulon

56. During sporulation in Bacillus subtilis, the response regulator that positively controls many genes needed for sporulation and negatively controls genes not needed during sporulation is

B. SpoOA.

67. Which of the following is not a mechanism of quorum sensing in Vibrio?

B. Stringent response

9. Which is a false statement regarding riboswitches?

B. The effector molecules that bind to riboswitches are proteins.

49. Which is false regarding the two-component regulatory system in bacteria?

B. The sensor kinase is phosphorylated by the response regulator when the extracellular environment changes.

61. When the Catabolite Activator Protein binds to its binding site in DNA, it

B. bends the DNA.

32. The site on the DNA to which a repressor protein binds is the __________.

B. operator

45. In two component regulatory systems, the response regulator typically receives a ____________ from the sensor kinase when it has been activated.

B. phosphoryl group

46. While standard two-component regulatory systems typically act to control gene transcription, phosphorelay systems can act either to control gene transcription or to control .

B. protein activity

59. The sensing of starvation that leads to sporulation in Bacillus subtilis is accomplished by a .

B. sensor kinase

47. The sensor kinase for the OmpF: OmpC two-component regulatory system is

B. the EnvZ protein.

13. In general, riboswitches regulate in Gram-negative bacteria such as Escherichia and in Gram-positive bacteria such as Bacillus.

B. translation; transcription

65. During the stringent response, ppGpp-regulated genes for amino acid biosynthesis have a(n) -rich promoter, thus forming a open initiation complex.

C. AT-rich; more stable

30. Which of the following is not a regulatory mechanism used to control the lactose operon in Escherichia coli?

C. Attenuation

4. Most E. coli antisense RNAs work with a protein called ______ to regulate their target mRNAs.

C. Hfq

64. Guanine tetraphosphate (ppGpp) is particularly associated with which process?

C. Stringent response in Escherichia

7. The __________ is a factor-independent termination site found in the leader region of certain operons, which, under the influence of ribosome behavior, controls the continued transcription of that operon.

C. attenuator

31. Enzymes that are expressed at a constant level all the time are said to be .

C. constitutive

52. In some circumstances, when two different carbon sources are available, growth will occur first using one carbon source, then after a short lag period, growth will resume using the second carbon source. This process is called __________ growth.

C. diauxic

10. With the E. coli trp operon where both repression and attenuation occur, the extent of regulation achieved by repression is _____________ the extent of regulation achieved by attenuation.

C. greater than

33. When bound to the DNA, the repressor protein usually prevents attachment of the RNA polymerase to the __________.

C. promoter

48. The E. coli lac operon has ________ operator sequences.

C. three

60. Cell-to-cell communication by quorum sensing has been shown to be important in the regulation of genes needed for A. virulence. B. biofilm production. C. plasmid transfer. D. All of the choices are correct.

D. All of the choices are correct.

76. It has been observed that when the sugar source changes in a growth medium, the growth rate of yeast vary widely in response. Some strains of yeast are slow to induce catabolic operons while other strains quickly synthesize proteins to process the new sugar. What might be one explanation for this difference in the growth rate of the strains?

D. Catabolic repression strategies of operons for using different sugars may vary among strains, thereby favoring initiation of transcription in one strain over another depending on the sugar.

6. What is the key factor determining whether or not attenuation will occur when transcription of the E. coli trp operon has been initiated?

D. The level of trp-tRNA that is charged with tryptophan

55. Acylhomoserine lactones used in quorum sensing regulate their own synthesis by a(n) ____________ system.

D. autoinduction

57. During the early stages of sporulation in Bacillus subtilis, ________ is active in the forespore and ________ is active in the mother cell.

D. σF; σE

11. Riboswitches regulate transcription, rather than translation, in cells.

FALSE

18. When tryptophan levels in a cell are low, a cell will stall transcription but continue translation of the tryptophan operon.

FALSE

21. Helix-turn-helix and zinc fingers are secondary structural motifs in DNA and RNA, respectively.

FALSE

26. The binding of arabinose to the AraC protein allows it to form a loop in the DNA upstream of the ara operon promoter.

FALSE

3. The THI-element is part of the operon that controls synthesis of thymine in mRNA.

FALSE

37. Scientists first focused on gene regulation at the level of translation, rather than transcription, because more was known about protein than nucleic acids at the time.

FALSE

39. The inducer for the E. coli lac operon is allolactose produced by the action of permease on lactose.

FALSE

40. In the presence of both glucose and lactose, the lactose repressor is not bound to the operator and the genes of the lactose operon are expressed.

FALSE

63. Two-component signal transduction systems are found in the Bacteria, but not in Archaea.

FALSE

73. During regulation of biofilm formation in Pseudomonas, cells leave the biofilm when levels of cyclic dimeric GMP are high.

FALSE

41. ____________ is used to measure the amount of a chemoattractant encountered over time.

Methylation

1. Small RNAs that regulate translation by binding to the leader region of mRNAs are called antisense RNAs.

TRUE

15. During tryptophan synthesis in Escherichia coli, the 1:2 attenuator sequence of mRNA is called the pause loop.

TRUE

16. During regulation by attenuation in the trp operon, if the pause and terminator loops form in mRNA, transcription is uncoupled to translation and protein synthesis is not occurring.

TRUE

42. One way to regulate gene expression is through the production of different sigma factors. These cause RNA polymerase to bind to different sets of promoters, thereby altering the pattern of gene expression.

TRUE

43. Gene regulation during sporulation in Bacillus subtilis involves BOTH temporal and spatial control.

TRUE

19. When arabinose is present in the environment, the AraC protein acts as a(n) ______________ for the E. coli ara operon.

activator or inducer

62. In order for high level expression of the E. coli lac operon to occur, a complex of catabolite activator protein and __________ must be bound to the DNA near the promoter.

cAMP or cyclic AMP

24. If a set of genes is repressed in the presence of the controlling substance, it is referred to as __________ control.

negative

25. If a set of genes is induced in the presence of the controlling substance, it is referred to as __________ control.

positive

44. A collection of genes or operons controlled by a common regulatory protein is called a(n) ___________ .

regulon

23. When there is no arabinose available in the environment, the AraC protein acts as a(n) ______________ for the E. coli ara operon.

repressor