Deck 18: Control of Gene Expression in Bacteria

Question 1

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

Answer 1

C

Question 2

Which of the following is a protein produced by a regulatory gene?

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

Answer 2

D

Question 3

The greatest expression of the lac operon occurs when lactose levels are ________.

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

Answer 3

C

Question 4

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. X-gal is likely to be a compound ________.

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

Question 5

Allolactose, an isomer of lactose, is formed in small amounts from lactose. An E. coli cell is presented for the first time with the sugar lactose (containing allolactose) as a potential food source. Which of the following occurs when lactose enters the cell?

A) The repressor protein attaches to the regulator.
B) Allolactose binds to the repressor protein.
C) Allolactose binds to the regulator gene.
D) The repressor protein and allolactose bind to RNA polymerase.
E) RNA polymerase attaches to the regulator.

Question 6

Suppose several genes are grouped together in a bacterial genome and the group results in a single enzyme. If one of these genes is mutated and the enzyme is no longer active, this gene must be part of ________.

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

Question 7

If you wanted to prevent a regulatory protein from changing gene expression, you would have to prevent physical contact between the protein and ________.

A) ribosomes
B) DNA
C) ribozymes
D) mRNA

Question 8

In negative control, a gene is switched off when ________.

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

Question 9

Imagine that you have set up a genetic screen to identify E. coli mutants that cannot metabolize the amino acid tryptophan for energy. 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 10

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

A) decrease the rate of gene expression
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 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) The lac operon would be transcribed continuously.
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 12

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 13

Most repressor proteins are allosteric. Which of the following binds with the repressor to alter its conformation?

A) inducer
B) promoter
C) RNA polymerase
D) transcription factor
E) cAMP

Question 14

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

Question 15

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 16

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 17

Altering patterns of gene expression in prokaryotes would most likely serve an organism's survival by ________.

A) organizing gene expression so that genes are expressed in a given order
B) allowing each gene to be expressed an equal number of times
C) allowing an organism to adjust to changes in environmental conditions
D) allowing young organisms to respond differently than more mature organisms
E) allowing environmental changes to alter a prokaryote's genome

Question 18

Although the expression of most genes is tightly regulated, some genes are expressed at roughly constant rates. Which of the following genes would you predict to be constitutively (constantly) 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 regulatory proteins

Question 19

The product of the lacI gene functions most like a car's ________.

A) parking brake
B) accelerator pedal
C) steering wheel
D) engine
E) gear shift

Question 20

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 21

Use this information to answer the question(s) below.
If she moves the promoter for the lac operon to the region between the beta galactosidase (lacZ) gene and the permease (lacY) gene, which of the following would be likely?

A) The three structural genes will be expressed normally.
B) RNA polymerase will no longer transcribe permease.
C) The operon will still transcribe the lacZ and lacY genes, but the mRNA will not be translated.
D) Beta galactosidase will not be produced.
E) The cell will continue to metabolize but more slowly.

Question 22

One interesting and surprising finding regarding the regulation of the ara operon is that it is under both positive and negative control. What protein is responsible for the dual action of this operon?

A) AraC is responsible for both the positive and negative control of the ara operon.
B) RNA polymerase is responsible for both the positive and negative control of the ara operon.
C) AraD is responsible for both the positive and negative control of the ara operon.
D) DNA polymerase is responsible for both the positive and negative control of the ara operon.
E) AraBAD is responsible for both the positive and negative control of the ara operon.

Question 23

In what general way are regulons regulated?

A) Regulons can be under either positive or negative control.
B) Regulons are under negative control exclusively.
C) Regulons are under positive control exclusively.
D) Global regulation of regulons depends on the regulatory guidance of RNA polymerase II.
E) Regulons are regulated by feedback translation loops.

Question 24

There is a mutation in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of these would characterize such a mutant?

A) It cannot bind to the operator.
B) It cannot make a functional repressor.
C) It cannot bind to the inducer.
D) It makes molecules that bind to one another.
E) It makes a repressor that binds CAP.

Question 25

Under what condition is the AraC protein an activator?

A) The AraC protein is an activator when it is bound to glucose.
B) The AraC protein is an activator when it is bound to lactose.
C) The AraC protein is an activator when it is bound to arabinose.
D) The AraC protein is an activator when it is bound to cyclic AMP.
E) The AraC protein is an activator when it is bound to any sugar molecule.

Question 26

Use this information to answer the question(s) below.
If she moves the repressor gene (lacI), along with its promoter, to a position at some several thousand base pairs away from its normal position, we would expect the ________.

A) repressor will no longer be made
B) repressor will no longer bind to the operator
C) repressor will no longer bind to the inducer
D) lac operon will be expressed continuously
E) lac operon will function normally

Question 27

The arabinose operon (ara) provides a particularly interesting example of ________ in that when arabinose is present in the environment, the operon is transcribed.

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

Question 28

When many genes of an organism are globally regulated, those genes are considered as regulon genes. What is the common theme of such genetic regulation?

A) Genes of regulons are silenced by a common repressor.
B) Genes of regulons are able to transcribe mRNA independent of regulation.
C) Genes of regulons are much more stable than non-regulon genes.
D) Genes of regulons are much less stable than non-regulon genes.
E) Individual genes of regulons are regulated independently of each other.

Question 29

Use this information to answer the question(s) below.
If she moves the operator to the far end of the operon, past the transacetylase (lacA) gene, which of the following would likely occur when the cell is exposed to lactose?

A) The inducer will no longer bind to the repressor.
B) The repressor will no longer bind to the operator.
C) The operon will never be transcribed.
D) The structural genes will be transcribed continuously.
E) The repressor protein will no longer be produced.