Deck 17: Control of Gene Expression in Bacteria

Question 1

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

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

Answer 1

C

Question 2

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

Answer 2

D

Question 3

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

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

Answer 3

B

Question 4

Full induction of the lac operon occurs when

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

Question 5

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

Question 6

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

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

Question 7

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

Question 8

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 color.What is X-Gal likely to be?

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

Question 9

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

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

Question 10

The product of the lacI gene is

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

Question 11

The trp repressor blocks transcription of the trp operon when the repressor

A)binds to inducer.
B)is not bound to inducer.
C)binds to tryptophan.
D)is not bound to tryptophan.
E)is not bound to the operator.

Question 12

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

Question 13

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

Question 14

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

Question 15

In negative control of transcription,a gene is activated when

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

Question 16

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

Question 17

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

A)transcriptional
B)translational
C)post-translational

Question 18

Recall from Chapter 11 that cyclin-dependent kinases are activated when they bind to a cyclin protein.This form of regulation is

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

Question 19

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

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

Question 20

Jacob and Monod were intellectually primed to draw the conclusions they did concerning regulation of the lac operon.In part,this was due to their fascination with mechanisms of enzyme regulation.They knew that the activity of some enzymes is regulated when their reaction product binds to the enzyme,changing its shape and,therefore,its activity.This knowledge allowed them to easily make the intellectual leap to propose

A)the existence of the CAP binding site.
B)allosteric regulation of the repressor.
C)positive regulation of the lac operon.
D)the existence of the operator.
E)co-transcribed and co-regulated genes of bacterial operons.

Question 21

How did Cronin et al.activate expression of tyrosinase to change the color of a white (albino)mouse to brown?

A)They exercised the mice vigorously.
B)They fed the mice a diet rich in glucose.
C)They added IPTG,a lactose analogue,to the drinking water.
D)They added cAMP to the drinking water.

Question 22

How does a regulatory protein that binds to a specific DNA sequence recognize this sequence?

A)The regulatory protein opens up the two strands of DNA and detects the bases on one of the strands.
B)The regulatory protein opens up the two strands of DNA and detects the bases on both strands.
C)The regulatory protein detects the portions of the base pairs that project into the grooves of double-stranded DNA.
D)The regulatory protein detects specific sequences in the sugar-phosphate backbone of one of the DNA strands.
E)The regulatory protein detects specific sequences in the sugar-phosphate backbone of both of the DNA strands.

Question 23

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

Question 24

E.coli adenylyl cyclase is most active when

A)extracellular glucose levels are low.
B)intracellular levels of lactose are low.
C)intracellular levels of lactose are high.
D)intracellular levels of cAMP are high.

Question 25

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

Question 26

Imagine that you've run a DNA footprinting analysis.Many closely spaced bands (DNA fragments)are seen in the lane of the gel prepared from DNA without protein.In the adjacent lane prepared from DNA mixed with protein,a subset of the bands is seen,but there is a large region where no bands are observed.This empty region represents

A)the region where protein did not bind to DNA.
B)the region where protein bound to DNA.
C)a region where there was no DNA for protein binding.
D)a region where protein was digested by the enzyme.

Question 27

The particular amino acid sequence in the helix-turn-helix domain of a regulatory protein

A)determines which DNA sequence is recognized by this protein.
B)determines which RNA polymerase will bind to the promoter.
C)controls the catalytic activity of an enzyme.
D)allows this protein to change shape when it binds cAMP.

Question 28

How does the inducer change the repressor's affinity for DNA?

A)Inducer binding changes the repressor's shape so that the promoter is bent from a rectangular to a loop-like shape.
B)Inducer binding changes the repressor's shape to alter the positioning of the repressor's DNA binding domains so they no longer interact with DNA.
C)Inducer binding makes the repressor's DNA binding domains more positively charged,so they can no longer bind the operator.
D)Inducer binding makes the repressor's DNA binding domains more negatively charged,so they can no longer bind the operator.

Question 29

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 β-galactosidase gene.
C)Cells are unable to cleave an indicator molecule even if lactose is available as an inducer.
D)Cells are able to cleave an indicator molecule even if lactose is absent as an inducer.

Question 30

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)lacZ⁻
B)lacY⁻
C)lacI⁻

Question 31

Use the following information when answering the corresponding question(s).
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 lacZ gene
B)the lacY gene
C)the lacI gene
D)the lac operator
E)CAP

Question 32

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

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

Question 33

Negative control occurs when

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

Question 34

A distinct part of a protein that often has a distinct function is a

A)substrate.
B)domain.
C)primary structure.
D)footprint.

Question 35

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

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

Question 36

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

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

Question 37

Extracellular glucose inhibits transcription of the lac operon by

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

Question 38

What is an inducer?

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