Deck 18: Control of Gene Expression in Bacteria

Question 1

Although the expression of most genes is tightly regulated, some genes are expressed at roughly constant rates i.e., constitutively). Which of the following genes would you predict to be constitutively expressed?

A) genes involved in the biosynthesis of the amino acid tryptophan
B) genes involved in the transport of the sugar maltose
C) genes that code for ribosomal RNAs
D) genes involved in the degradation of arabinose, a sugar
E) genes involved in the degradation of tryptophan

Answer 1

C

Question 2

Full induction of the lac operon occurs when

A) lactose levels are high and glucose levels are low.
B) lactose levels are low and glucose levels are high.
C) lactose levels are high and glucose levels are high.
D) lactose levels are low and glucose levels are low.

Answer 2

A

Question 3

Imagine that you've set up a genetic screen to identify E. coli mutants that cannot metabolize the amino acid tryptophan. Beginning with a master plate containing many colonies, you prepare replica plates on medium with glucose or tryptophan as the only energy source. You would look for colonies that

A) can grow only on the plates with tryptophan.
B) cannot grow on either type of media.
C) can grow on both types of media.
D) can grow only on the plates with glucose.

Answer 3

D

Question 4

The product of the lacI gene is most like a car's

A) parking brake.
B) engine.
C) accelerator pedal.
D) wheels.
E) steering wheel.

Question 5

Which of the following levels of gene expression allows the most rapid response to environmental change?

A) translational control
B) transcriptional control
C) post- translational control

Question 6

A compound known as X- Gal is widely used in molecular genetic research. When wild- type normal) E. coli is grown on medium containing X- Gal, the bacterial colonies turn blue. In contrast, when lacZ mutants are grown on medium containing X- Gal, the bacterial colonies remain their normal white colour. What is X- Gal likely to be?

A) a compound chemically similar to glucose
B) a compound chemically similar to lactose
C) a compound chemically similar to galactose
D) a compound that cannot be transported into lacZ mutants
E) a compound that can only be transported into lacA mutants

Question 7

In gene expression, when does negative control occur? When

A) lactose is transported into the cell.
B) a kinase adds a phosphate to DNA.
C) an activator is removed from DNA and shuts down transcription.
D) DNA is coiled too tightly for genes to be transcribed.
E) a repressor binds to DNA and shuts down transcription.

Question 8

In negative control of transcription, a gene is activated when

A) lactose is transported into the cell.
B) a regulatory protein is removed from DNA.
C) a kinase adds a phosphate to DNA.
D) a regulatory protein binds to DNA.

Question 9

E. coli and many other bacteria of the human gut need to have fine- tuned regulation of gene expression in order to

A) grow.
B) metabolize any nutrient.
C) evolve.
D) replicate their DNA.
E) effectively compete for space and nutrients.

Question 10

Imagine that you've added the same indicator used by Monod to E. coli colonies growing on a plate with glucose and no lactose. One colony is yellow and the remainders are white. This result suggests that cells of the yellow colony

A) cannot metabolize lactose.
B) cannot transport lactose into the cell.
C) have constitutively active lacZ and lacY genes.
D) cannot activate either the lacZ or lacY gene.
E) can activate the lacY gene but cannot active the lacZ gene.

Question 11

According to the lac operon model proposed by Jacob and Monod, what is predicted to occur if the operator is removed from the operon?

A) Galactosidase permease would be produced, but would be incapable of transporting lactose.
B) The lac operon would be transcribed constitutively.
C) Only lacZ would be transcribed.
D) Only lacY would be transcribed.

Question 12

An E. coli cell without a functional lacI gene is expected to

A) be unable to metabolize lactose within the cell.
B) always produce fi- galactosidase.
C) never produce fi- galactosidase.
D) be unable to transport lactose into the cell.

Question 13

Recall that cyclin- dependent kinases are activated when they bind to a cyclin protein. This form of regulation is

A) post- translational control.
B) transcriptional control.
C) constitutive control.
D) translational control.

Question 14

In the first step of their experiments, Jacob and Monod treated E. coli cells with UV light or X- rays in order to

A) decrease the number of viable cells.
B) increase the frequency of mutations in all genes.
C) selectively mutate the lac operon, leaving all other genes unmutated.
D) induce DNA repair enzymes.

Question 15

Catabolite activator protein CAP) activity is controlled by cAMP at the level.

A) post- translational
B) translational
C) transcriptional

Question 16

The product of the lacI gene is

A) fi- galactosidase.
B) an enzyme.
C) a transport protein embedded within the membrane.
D) the repressor.

Question 17

Bacterial and eukaryotic cells primarily control gene expression at the level of transcription. If instead cells exerted control of gene expression primarily at the post- translational level, what would be different?

A) Genes would no longer be transcribed.
B) The ability to rapidly respond to environmental change would be reduced.
C) Cells would expend significantly more energy.
D) Translation of mRNA into protein would not occur.

Question 18

A group of genes that are regulated together and transcribed into a single mRNA is

A) an inducer.
B) an intron.
C) an activator.
D) a repressor.
E) an operon.

Question 19

Which of the following, when taken up by a cell, binds to a repressor so that the repressor no longer binds to the operator?

A) inducer
B) corepressor
C) promoter
D) ubiquitin
E) repressor

Question 20

Imagine that you discover a bacterial operon involved in the synthesis of vitamin B₁₂. This operon is regulated by a repressor protein that binds to an operator sequence. Vitamin B₁₂ is the allosteric effector of the repressor
-the molecule that binds to the repressor to affect its activity. Predict how vitamin B₁₂ will influence repressor activity.

A) When vitamin B₁₂ binds to the repressor, the repressor binds to the operator.
B) When vitamin B₁₂ binds to the repressor, the repressor can bind to RNA polymerase.
C) When vitamin B₁₂ binds to the repressor, the repressor cannot bind to RNA polymerase.
D) When vitamin B₁₂ binds to the repressor, the repressor cannot bind to the operator.

Question 21

What is an inducer?

A) A product that stimulates gene expression in a reaction.
B) A substrate that inhibits gene expression in a reaction.
C) A substrate that stimulates gene expression in a reaction.
D) A product that inhibits gene expression in a reaction.

Question 22

What proteins) is/are responsible for the dual positive and negative control of the ara operon?

A) AraD
B) AraC
C) RNA polymerase
D) AraBAD
E) DNA polymerase

Question 23

CAP is said to be responsible for positive regulation of the lac operon because

A) Extracellular glucose levels influence the ability of CAP to bind to the CAP binding site.
B) CAP prevents binding of the repressor to the operator.
C) CAP bound to the CAP binding site increases the frequency of transcription initiation.
D) CAP binds the CAP binding site.
E) CAP binds cAMP.

Question 24

Which of the following environments would most likely lead to the transcription of the lactose operon?

A) The cyclic AMP level is high, and the lactose level is low.
B) The cyclic AMP and lactose levels are both high within the cell.
C) There is glucose but no lactose in the cell.
D) There is more glucose in the cell than lactose.
E) The cyclic AMP levels are low.

Question 25

To date, several lactose metabolism mutants have been found in Escherichia coli. One of these mutants has a phenotype in which the cell cannot accumulate lactose because no lactose permease protein is present. What genotype would be associated with this mutation?

A) lacI^-
B) lacZ^-
C) lacY^-

Question 26

Negative control occurs when

A) a regulatory protein binds to RNA polymerase and shuts down the process of transcription.
B) a regulatory protein binds to RNA and shuts down the process of transcription.
C) a regulatory protein binds to DNA and shuts down the process of transcription.
D) a regulatory protein binds to DNA polymerase and shuts down the process of transcription.

Question 27

What is the common theme of global gene regulation?

A) Genes of regulons are less stable than nonregulon genes.
B) Genes of regulons are transcribed independently of regulation.
C) Genes of regulons are more stable than nonregulon genes.
D) Genes of regulons are controlled by a single type of regulatory protein.
E) Each gene of a regulons is regulated independently.

Question 28

Extracellular glucose inhibits transcription of the lac operon by

A) weakening the binding of repressor to the operator.
B) inhibiting RNA polymerase from opening the strands of DNA to initiate transcription.
C) reducing the levels of intracellular cAMP.
D) strengthening the binding of repressor to the operator.
E) activating adenylyl cyclase.

Question 29

Use the following information when answering the corresponding questions).
The lac operon is used in countless ways for genetics research and biotechnology. One important use of the lac operon is to regulate the expression of cloned genes. In this application, some regulatory elements of the operon are fused to the cloned gene that is to be regulated. One application of such technology was reported by Cronin et al., The lac operator- repressor system is functional in the mouse, Genes and Development 15 2001):1506-17. These investigators fused a portion of the lac operon to the mouse tyrosinase gene, a gene required for pigment production. This recombinant DNA, composed of E. coli lac operon sequences and the mouse tyrosinase gene, was introduced into albino mice using techniques described in Chapter 19. Using the lac operon regulatory sequences, the investigators were able to regulate tyrosinase gene expression. In fact, they were able to convert albino white) mice into brown mice. The following questions ask you to use your knowledge of the lac operon to deduce how Cronin et al. were able to regulate tyrosinase gene expression in mice.
Introducing the recombinant lac operon/mouse tyrosinase DNA into mice is only half of the equation for regulating tyrosinase. In addition to lac operon/mouse tyrosinase DNA, what other gene must be added to mice to regulate tyrosinase expression?

A) the lacY gene
B) the lacI gene
C) the lac operator
D) the lacZ gene

Question 30

When arabinose is present in the environment, the arabinose operon is transcribed. What is this an example of?

A) negative control
B) positive control
C) push forward control
D) reverse transcription
E) positive translation

Question 31

The situation in which an active regulatory protein "turns on" gene expression is an example of which of the following?

A) negative control
B) constitutive gene elements
C) positive control
D) a mutation
E) feedback inhibition

Question 32

What type of control is the SOS response regulon under?

A) only positive control
B) feedback transcription
C) only negative control
D) feedback inhibition
E) both positive and negative control

Question 33

If the genetically engineered albino mice were given no special treatment, how would the tyrosinase gene be expressed?

A) It would be transcribed to a high level.
B) It would not be transcribed.
C) It would be transcribed to a moderate level.

Question 34

Controlling the production of a pigment is interesting, but in itself seems more a stunt than a valuable research endeavor. What is the broader significance of the results of Cronin et al.?

A) This same genetic system potentially can be used to control the expression of genes involved in weight control.
B) The same genetic system can be used to create black as well as brown mice.
C) This same genetic system potentially can be used to control the expression of almost any gene.
D) This same genetic system potentially can be used to treat hair loss in mice and humans.

Question 35

A technique that can be used to identify mutant bacterial cells is called

A) replica plating.
B) master plating.
C) indicator plating.
D) comparison plating.

Question 36

Under what condition is the AraC protein an activator? When AraC is bound to

A) cyclic AMP.
B) any sugar molecule.
C) lactose.
D) arabinose.
E) glucose.

Question 37

Which phenotype would be observed in an E. coli cell with the lacY- genotype?

A) Cells would not be able to accumulate lactose due to the absence of the lactose permease membrane protein.
B) Cells would not be able to accumulate lactose due to the presence of a defect in the fi- galactosidase gene.
C) Cells are able to cleave an indicator molecule even if lactose is absent as an inducer.
D) Cells are unable to cleave an indicator molecule even if lactose is available as an inducer.

Question 38

Use the following information when answering the corresponding questions).
The lac operon is used in countless ways for genetics research and biotechnology. One important use of the lac operon is to regulate the expression of cloned genes. In this application, some regulatory elements of the operon are fused to the cloned gene that is to be regulated. One application of such technology was reported by Cronin et al., The lac operator- repressor system is functional in the mouse, Genes and Development 15 2001):1506-17. These investigators fused a portion of the lac operon to the mouse tyrosinase gene, a gene required for pigment production. This recombinant DNA, composed of E. coli lac operon sequences and the mouse tyrosinase gene, was introduced into albino mice using techniques described in Chapter 19. Using the lac operon regulatory sequences, the investigators were able to regulate tyrosinase gene expression. In fact, they were able to convert albino white) mice into brown mice. The following questions ask you to use your knowledge of the lac operon to deduce how Cronin et al. were able to regulate tyrosinase gene expression in mice.
The tyrosinase gene used by Cronin et al. contained the protein- coding sequence and the normal mouse regulatory sequences. These regulatory sequences provide positive control of tyrosinase transcription. If nothing else is done to this DNA and it is introduced into a mouse, tyrosinase will always be expressed. Because the goal was to regulate expression of tyrosinase, what portion of the lac operon do you think was added to this mouse gene?

A) the lacI gene
B) the lacZ gene
C) CAP
D) the lacY gene
E) the lac operator