Question 1

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

Accepted Answer

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

Question 2

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

Accepted Answer

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

Question 3

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?

Accepted Answer

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. A

Question 4

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 ________.

Accepted Answer

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 5

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

Accepted Answer

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

Question 6

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

Accepted Answer

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

Question 7

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?

Accepted Answer

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 8

Under what condition is the AraC protein an activator?

Accepted Answer

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 9

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

Accepted Answer

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

Question 10

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?

Accepted Answer

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 11

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

Accepted Answer

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 12

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

Accepted Answer

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 13

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?

Accepted Answer

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 14

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 ________.

Accepted Answer

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

Question 15

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

Accepted Answer

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 16

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

Accepted Answer

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 17

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 ________.

Accepted Answer

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 18

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

Accepted Answer

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

Question 19

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

Accepted Answer

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

Question 20

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?

Accepted Answer

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.

Exam 18: Control of Gene Expression in Bacteria