Deck 14: Regulation of Gene Expression in Bacteria and Bacteriophages

Question 1

Which of the following can be mutated to result in constitutive expression from the lac operon?

A)lacZ and lacP
B)lacZ and lacI
C)lacO and lacI
D)lacO and lacZ
E)lacI and lacY

Answer 1

C

Question 2

During the attenuation of the trp operon, which stem loop leads to polycistronic mRNA synthesis during tryptophan starvation?

A)1-3 (antitermination)stem loop
B)3-4 (termination)stem loop
C)1-2 (pause)stem loop
D)2-3 (antitermination)stem loop
E)2-4 (termination)stem loop

Answer 2

D

Question 3

The enzyme β-galactosidase catalyzes what reaction?

A)allolactose → glucose + lactose
B)lactose → glucose + fructose
C)lactose → galactose + glucose
D)glucose → galactose + lactose
E)galactose → glucose + lactose

Answer 3

C

Question 4

You want to design a repressor protein mutant. Which protein domain is the best target for preventing binding of the corepressor?

A)DNA-binding domain
B)allosteric domain
C)promoter domain
D)helix-turn-helix domain
E)activator binding site

Question 5

Which region of the lac operon would you target if you want to disrupt the -10 and -35 consensus sequences?

A)lacZ
B)lacY
C)lacI
D)lacP
E)lacO

Question 6

In the absence of tryptophan, __________.

A)the inactive repressor cannot bind trpO, so operon gene transcription occurs
B)the active repressor binds trpP, so operon gene transcription is repressed
C)the inducer cannot bind trpO, so operon gene transcription occurs
D)the active repressor cannot bind trpO, so operon gene transcription is attenuated
E)the repressor binds the corepressor, and operon gene transcription occurs

Question 7

Which structural gene of the lac operon can be mutated without affecting the cell's ability to break down lactose?

A)lacZ
B)lacY
C)lacA
D)lacP
E)lacO

Question 8

Which of these haploid strains produces permease but does not produce β-galactosidase?

A)I ^- P⁺ O⁺ Z⁺ Y⁺
B)I⁺ P⁺ O⁺ Z ^- Y⁺
C)I ^- P⁺ O⁺ Z ^- Y ^-
D)I⁺ P⁺ O ^- Z⁺ Y⁺
E)I ^- P⁺ O⁺ Z⁺ Y ^-

Question 9

The presence of which combination of molecules would lead to active transcription of an operon?

A)activator + corepressor
B)activator + repressor
C)inducer + corepressor
D)repressor + corepressor
E)activator + inducer

Question 10

A bacterium is unable to transport lactose into the cell to be broken down. Which gene is likely mutated in this bacterium?

A)lacZ
B)lacY
C)lacI
D)lacP
E)lacO

Question 11

In the presence of glucose, where is the lac repressor bound?

A)lacZ
B)lacO
C)lacP
D)lacI
E)The lac repressor is not bound to the operon.

Question 12

If you wanted to prevent a cell from entering the lysogenic pathway, which gene controlled by P_RM would you target for inactivation?

A)cro
B)Q
C)cI
D)cII
E)O

Question 13

Which region of the λ phage genome enables the linear chromosome to circularize when it enters a host cell?

A)cohesive (cos)site
B)IS10
C)early operators
D)integrase (int)gene
E)excisionase (xis)gene

Question 14

Which of these haploid strains produces β-galactosidase constitutively but does not produce permease?

A)I ^- P⁺ O⁺ Z⁺ Y⁺
B)I⁺ P⁺ O⁺ Z ^- Y ^-
C)I ^- P⁺ O⁺ Z ^- Y⁺
D)I⁺ P⁺ O ^- Z⁺ Y⁺
E)I ^- P⁺ O⁺ Z⁺ Y ^-

Question 15

In negative control, what molecule would you expect to find bound to the operator if there is no transcription?

A)activator
B)repressor
C)inducer
D)corepressor
E)RNA polymerase

Question 16

Which of the following mutants are noninducible?

A)lacI^S
B)lacI ^-
C)lacI⁺
D)lacO^C
E)lacO⁺

Question 17

Which sigma factor, encoded by the rpoH gene, is active at high temperatures?

A)σ⁷⁰
B)σ³²
C)σ⁴⁵
D)σ³⁷
E)σ⁵⁰

Question 18

In λ phage, which protein, the product of the cI gene, blocks the transcription required to initiate the lytic cycle?

A)cro
B)repressor
C)enhancer
D)integrase
E)operator

Question 19

Which enzyme is responsible for integration of a temperate phage into a host genome?

A)β-galactosidase
B)transposase
C)integrase
D)transacetylase
E)permease

Question 20

In the lac operon, what acts as the inducer?

A)glucose
B)permease
C)allolactose
D)β-galactosidase
E)transacetylase

Question 21

Mutations of trpL decrease the efficiency of transcriptional regulation by disrupting the formation of which stem-loop structure?

Question 22

Antisense control of translation involves the regulation of which enzyme produced by bacterial insertion sequence IS10?

Question 23

For each of the following E. coli partial diploid strains, indicate whether expression of
$\beta$ -galactosidase and permease is inducible (I), constitutive (C), or negative (no product made)(N). Assume glucose levels are very low. Which of the strains are able to use lactose as their sole carbon source?

Question 24

When both glucose and lactose are available in the growth medium, the presence of which molecule is capable of inducing basal transcription of the lac operon?

Question 25

What would be the phenotype of an int⁻ $\lambda$ mutant?

A)The phage would not be able to undergo the lytic cycle, but could lysogenize.
B)Both lytic and lysogenic pathways would be inactivated.
C)The phage would be able to enter the lytic cycle, but would not be able to lysogenize.
D)The phage would be able to lysogenize but would not be able to be induced to resume the lytic cycle.
E)The cell would build up high levels of $\lambda$ repressor, so lysogeny would be maintained.

Question 26

Which molecule functions as the corepressor in the trp operon?

Question 27

Binding of which complex increases the ability of RNA polymerase to transcribe the lac operon?

Question 28

Which enzyme is the product of the lacZ gene?

Question 29

If a corepressor is inhibited, what effect would you expect to see in the operon?

Question 30

Regulation of transcription of bacterial genes takes place at which two levels?

Question 31

What are the names of the three possible alternative stem loops that can form in mRNA?

Question 32

Which part of the lac operon produces a regulatory protein that is trans-acting?

Question 33

Which part of the lac operon is cis-dominant?

Question 34

Bacteria grown at 45°C initiate expression of which two types of proteins?

Question 35

In the trp operon, where is the attenuator region located?

Question 36

What is the process by which a bacterium switches from a lysogenic to lytic cycle?

Question 37

The genetic switch controlling whether a bacterium enters the lytic or lysogenic cycle relies on the binding of which two proteins?

Question 38

What are the two active sites or "domains" on a repressor protein?

Question 39

Which proteins facilitate RNA polymerase binding at promoters?

Question 40

Catabolite repression refers to the repression of the lac operon in the presence of which catabolite?

Question 41

Changing conformation at the active site as a result of binding a substance at a different site is known as ________.

Question 42

Most of the regulation of gene expression in bacteria occurs at the ________ level.

Question 43

Suppose a $\lambda$ phage infected a protease-deficient bacterial cell. Would the lytic or lysogenic life cycle be favored? Why?

Question 44

In λ phage, entry into the ________ cycle requires transcription of late genes.

Question 45

Explain how transcriptional control by the NrpR protein of the archaeon Methanococcus maripaludis is similar to transcriptional control in bacteria.
It is known that 2-oxoglutarate (2OG)is used by cells as an indicator of nitrogen deficiency. Based on what you know about effector molecules in bacterial operons, how would 2OG behave in
M. maripaludis (as an inducer, a corepressor, etc.)and what effect would this molecule have on NrpR binding?

Question 46

What is the purpose of the lac operon, and under what circumstances is it activated? Describe the structure of the lac operon, including the repressor protein, structural genes, and regulatory regions of the operon. What is the role of catabolite repression in the lac operon?

Question 47

What protein cleaves the λ repressor monomers to inactivate the repressor protein, and is activated by DNA-damaging agents?

Question 48

Bacterial translation is inhibited by ________ RNA, which is complementary to a portion of a specific mRNA.

Question 49

What is the role of cis-acting and trans-acting factors in transcription? Explain how these factors play a role in the lac operon, and discuss how complementation can be used to identify where the mutations have occurred (structural genes versus regulatory regions). Which type of mutations
can be complemented by a second gene with normal function? Are I^S and O^C mutants cis- or
trans-acting?

Question 50

What would be the consequences to a $\lambda$ phage that lysogenized in a recA⁻ bacterial cell? Explain why this would occur.

Question 51

In E. coli, the cya gene encodes adenylate cyclase. Will cells that are cya⁻ be able to grow on medium that contains lactose as the sole carbon source? Why or why not?

Question 52

Expression of a(n)________ alters gene transcription in E. coli by activating transcription of specialized heat stress response genes.

Question 53

DNA-binding proteins exert control by binding DNA at specific sequences. Describe how DNA and protein interact at the molecular level. Are proteins able to identify specific DNA sequences, or do they bind to all regions with equal frequency? What motifs are commonly found in DNA-binding proteins?

Question 54

Describe the differences between inducible and repressible operons. How does attenuation differ from inducible or repressible operons?
Which of the two inducible operons you've studied would be active if a cell has the following food sources?
a. only lactose
b. only glucose
c. lactose and glucose