Question 1

In positive control of several sugar-metabolism-related operons, the catabolite activator protein (CAP)binds to DNA to stimulate transcription. What causes an increase in CAP?
A) increase in glucose and increase in cAMP
B) decrease in glucose and increase in cAMP
C) increase in glucose and decrease in cAMP
D) decrease in glucose and increase in repressor
E) decrease in glucose and decrease in repressor

Accepted Answer

When glucose levels are low, cAMP levels increase. CAP requires cAMP to bind to DNA and stimulate transcription. Therefore, a decrease in glucose and an increase in cAMP lead to an increase in CAP activity.

Question 2

Which of the following is a protein produced by a regulatory gene?
A) operon
B) inducer
C) promoter
D) repressor
E) corepressor

Accepted Answer

A repressor is a protein produced by a regulatory gene that binds to the operator region of DNA, preventing RNA polymerase from transcribing the genes.

Question 3

Which of the following mechanisms is (are)used to coordinate the expression of multiple, related genes in eukaryotic cells?
A) Genes are organized into clusters, with local chromatin structures influencing the expression of all the genes at once.
B) The genes share a common intragenic sequence, and allow several activators to turn on their transcription, regardless of location.
C) The genes are organized into large operons, allowing them to be transcribed as a single unit.
D) A single repressor is able to turn off several related genes.
E) Environmental signals enter the cell and bind directly to promoters.

Accepted Answer

Genes that are related in function or involved in the same pathway are often organized into clusters in the genome. These clusters allow for coordinated regulation of gene expression through shared chromatin structure and regulation by common transcription factors. This is known as "gene clustering" or "gene co-regulation".

Question 4

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.

Accepted Answer

A super-repressor mutation typically results in a repressor that cannot bind to the inducer (such as allolactose in the lac operon), thus remaining permanently bound to the operator and repressing the operon continuously.

Question 5

When DNA is compacted by histones into 10-nm and 30-nm fibers, the DNA is unable to interact with proteins required for gene expression. Therefore, to allow for these proteins to act, the chromatin must constantly alter its structure. Which processes contribute to this dynamic activity?
A) DNA supercoiling at or around H1
B) methylation and phosphorylation of histone tails
C) hydrolysis of DNA molecules where they are wrapped around the nucleosome core
D) accessibility of heterochromatin to phosphorylating enzymes
E) nucleotide excision and reconstruction

Accepted Answer

Methylation and phosphorylation of histone tails contribute to dynamic activity of chromatin by altering the charge and structure of the histone tail, which ultimately affects the overall structure of chromatin. This modification can either activate or repress gene expression by creating or blocking binding sites for transcription factors. The other options listed (A, C, D, and E) are not correct as DNA supercoiling, hydrolysis of DNA molecules, accessibility of heterochromatin, and nucleotide excision and reconstruction do not directly contribute to the dynamic activity of chromatin.

Question 6

The lactose operon is likely to be transcribed when
A) there is more glucose in the cell than lactose.
B) the cyclic AMP levels are low.
C) there is glucose but no lactose in the cell.
D) the cyclic AMP and lactose levels are both high within the cell.
E) the cAMP level is high and the lactose level is low.

Accepted Answer

The lactose operon is regulated by both lactose and glucose levels. When glucose levels are high, transcription of the lactose operon is inhibited. However, when glucose levels are low, cyclic AMP (cAMP) levels are high and can bind to the CAP protein, allowing it to bind to the upstream promoter region in the lactose operon, thus enhancing transcription. Additionally, when lactose is present, it binds to the lac repressor protein and prevents it from binding to the operator region, allowing RNA polymerase to transcribe the genes in the operon. Therefore, the lactose operon is likely to be transcribed when both cyclic AMP and lactose levels are high within the cell. Choice D is the only option that accurately describes this scenario.

Question 7

For a repressible operon to be transcribed, which of the following must occur?
A) A corepressor must be present.
B) RNA polymerase and the active repressor must be present.
C) RNA polymerase must bind to the promoter, and the repressor must be inactive.
D) RNA polymerase cannot be present, and the repressor must be inactive.
E) RNA polymerase must not occupy the promoter, and the repressor must be inactive.

Accepted Answer

In a repressible operon, the repressor is normally bound to the operator, preventing RNA polymerase from binding to the promoter and transcribing the genes. However, if the substrate for the pathway controlled by the operon is present, it can bind to the repressor, causing a change in its conformation that allows it to no longer bind to the operator. This allows RNA polymerase to bind to the promoter and transcribe the genes. Therefore, for a repressible operon to be transcribed, RNA polymerase must bind to the promoter, and the repressor must be inactive.

Question 8

The role of a metabolite that controls a repressible operon is to
A) bind to the promoter region and decrease the affinity of RNA polymerase for the promoter.
B) bind to the operator region and block the attachment of RNA polymerase to the promoter.
C) increase the production of inactive repressor proteins.
D) bind to the repressor protein and inactivate it.
E) bind to the repressor protein and activate it.

Accepted Answer

The role of a metabolite in a repressible operon is to bind to the repressor protein and activate it. This activated repressor can then bind to the operator region, preventing RNA polymerase from transcribing the genes in the operon.

Question 9

The tryptophan operon is a repressible operon that is
A) permanently turned on.
B) turned on only when tryptophan is present in the growth medium.
C) turned off only when glucose is present in the growth medium.
D) turned on only when glucose is present in the growth medium.
E) turned off whenever tryptophan is added to the growth medium.

Accepted Answer

The tryptophan operon is a repressible operon that is turned off (repressed) when tryptophan is present in sufficient quantities. This is because tryptophan acts as a corepressor, binding to the repressor protein and enabling it to bind to the operator, shutting off the operon.

Question 10

Genomic imprinting, DNA methylation, and histone acetylation are all examples of
A) genetic mutation.
B) chromosomal rearrangements.
C) karyotypes.
D) epigenetic phenomena.
E) translocation.

Accepted Answer

Genomic imprinting, DNA methylation, and histone acetylation are all examples of epigenetic phenomena - changes in gene expression without changing the DNA sequence itself. Epigenetic modifications affect how genes are read by the cellular machinery, and can be influenced by a variety of environmental and developmental factors.

Question 11

If glucose is available in the environment of E. coli, the cell responds with a very low concentration of cAMP. When the cAMP increases in concentration, it binds to CAP. Which of the following would you expect to be a measurable effect?
A) decreased concentration of the lac enzymes
B) increased concentration of the trp enzymes
C) decreased binding of the RNA polymerase to sugar metabolism-related promoters
D) decreased concentration of alternative sugars in the cell
E) increased concentrations of sugars such as arabinose in the cell

Accepted Answer

The answer of If glucose is available in the environment...

Question 12

Altering patterns of gene expression in prokaryotes would most likely serve the organism's survival in which of the following ways?
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 the organism to adjust to changes in environmental conditions
D) allowing young organisms to respond differently from more mature organisms
E) allowing environmental changes to alter the prokaryote's genome

Accepted Answer

Altering patterns of gene expression allows prokaryotes to adjust to changes in environmental conditions, increasing their chances of survival. By changing which genes are expressed and at what levels, the organism can produce proteins and enzymes that help it adapt to its changing surroundings.

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

Accepted Answer

Inducer molecules bind to repressor proteins and cause a conformational change that prevents the repressor from binding to the operator region. This allows RNA polymerase to bind to the promoter and initiate transcription of the gene.

Question 14

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 the 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.

Accepted Answer

Allolactose binds to the repressor protein, causing a conformational change that releases the repressor protein from the operator region of the DNA. This allows RNA polymerase to access the structural genes and initiate transcription to produce the necessary enzymes for lactose metabolism.

Question 15

A lack of which molecule would result in the cell's inability to "turn off" genes?
A) operon
B) inducer
C) promoter
D) ubiquitin
E) corepressor

Accepted Answer

A corepressor is a molecule that binds to a repressor protein, converting it into its active form and causing repression of gene expression. Without a corepressor, the repressor cannot bind to the operon and the genes cannot be turned off.

Question 16

Which of the following, when taken up by the cell, binds to the repressor so that the repressor no longer binds to the operator?
A) ubiquitin
B) inducer
C) promoter
D) repressor
E) corepressor

Accepted Answer

An inducer is a molecule that when taken up by the cell, binds to the repressor so that the repressor no longer binds to the operator. This allows RNA polymerase to bind to the promoter and initiate transcription of the genes under the control of the operator. Ubiquitin is not involved in gene regulation, it is involved in protein degradation. The promoter is a DNA sequence where RNA polymerase binds to initiate transcription. The repressor is a protein that binds to the operator and inhibits transcription. A corepressor is a molecule that binds to the repressor and enhances its binding to the operator.

Question 17

Transcription of the structural genes in an inducible operon
A) occurs continuously in the cell.
B) starts when the pathway's substrate is present.
C) starts when the pathway's product is present.
D) stops when the pathway's product is present.
E) does not result in the production of enzymes.

Accepted Answer

Transcription of the structural genes in an inducible operon starts when the pathway's substrate is present. This is because inducible operons are normally turned off and need to be induced by specific molecules, called inducers, which are usually the substrate of the pathway. Only then can the transcription of the structural genes occur and result in the production of enzymes.

Question 18

In response to chemical signals, prokaryotes can do which of the following?
A) turn off translation of their mRNA
B) alter the level of production of various enzymes
C) increase the number and responsiveness of their ribosomes
D) inactivate their mRNA molecules
E) alter the sequence of amino acids in certain proteins

Accepted Answer

Prokaryotes can alter the level of production of various enzymes in response to chemical signals. This is done by regulating gene expression, either by increasing or decreasing the transcription of specific genes. This allows prokaryotes to adapt to changes in their environment and is a form of gene regulation known as inducible gene expression. The other options are not characteristics of prokaryotic response to chemical signals.

Question 19

If you were to observe the activity of methylated DNA, you would expect it to
A) be replicating nearly continuously.
B) be unwinding in preparation for protein synthesis.
C) have turned off or slowed down the process of transcription.
D) be very actively transcribed and translated.
E) induce protein synthesis by not allowing repressors to bind to it.

Accepted Answer

Methylation of DNA is known to be associated with gene silencing or turning off certain genes. The presence of methyl groups on DNA can prevent the binding of transcription factors and RNA polymerase, which are necessary for transcription to occur. Therefore, observing the activity of methylated DNA would lead you to expect a slowing down or turning off of transcription.

Question 20

A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would result in
A) continuous transcription of the structural gene controlled by that regulator.
B) complete inhibition of transcription of the structural gene controlled by that regulator.
C) irreversible binding of the repressor to the operator.
D) inactivation of RNA polymerase by alteration of its active site.
E) continuous translation of the mRNA because of alteration of its structure.

Accepted Answer

The regulatory gene in a repressible operon codes for the repressor protein which inhibits the transcription of structural genes when a specific molecule is present in the cell. If the regulatory gene is mutated and becomes inactive, then the repressor protein will not be produced, leading to the continuous transcription of the structural gene controlled by that regulator.

Quiz 18: Regulation of Gene Expression

In positive control of several sugar-metabolism-related operons, the catabolite activator protein (CAP) binds to DNA to stimulate transcription. What causes an increase in CAP?

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

Which of the following mechanisms is (are) used to coordinate the expression of multiple, related genes in eukaryotic cells?

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?

When DNA is compacted by histones into 10-nm and 30-nm fibers, the DNA is unable to interact with proteins required for gene expression. Therefore, to allow for these proteins to act, the chromatin must constantly alter its structure. Which processes contribute to this dynamic activity?

The lactose operon is likely to be transcribed when

For a repressible operon to be transcribed, which of the following must occur?

The role of a metabolite that controls a repressible operon is to

The tryptophan operon is a repressible operon that is

Genomic imprinting, DNA methylation, and histone acetylation are all examples of

If glucose is available in the environment of E. coli, the cell responds with a very low concentration of cAMP. When the cAMP increases in concentration, it binds to CAP. Which of the following would you expect to be a measurable effect?

Altering patterns of gene expression in prokaryotes would most likely serve the organism's survival in which of the following ways?

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

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 the lactose enters the cell?

A lack of which molecule would result in the cell's inability to "turn off" genes?

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

Transcription of the structural genes in an inducible operon

In response to chemical signals, prokaryotes can do which of the following?

If you were to observe the activity of methylated DNA, you would expect it to

A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would result in