Chapter 18: Control of Gene Expression in Bacteria

sections of the lac operon

(Lac I gene (codes for repressor)(not actually part of operon)) promoter operator lac Z-beta galactosidase Lac Y-galactoside permease lac A

A multistep process of converting information that is archived in DNA into molecules that actually do things in the cell is termed ________. gene expression transcriptional control global gene regulation translational control

1

An Escherichia coli cell with a mutation in the catabolite activator protein (CAP) gene such that the CAP is unable to bind to a regulatory sequence upstream of the lac promoter would be expected to __________. have lower levels of transcription of the lac operon genes than a wild-type E. coli cell have the same levels of transcription of the lac operon genes as a wild-type E. coli cell have higher levels of transcription of the lac operon genes than a wild-type E. coli cell have high levels of transcription of the lac operon genes even in the absence of lactose

1

Cotranscription of the lac operon involves which of the following genes? lacZ, lacY, lacA lacZ, lacY, lacI lacZ, lacI, lacY lacI, lacY, lacZ

1

Gene expression is __________. the process of converting information in DNA into molecules that the cell needs to function via the processes of transcription and translation the ability to alter the amount of DNA in a cell necessary for a particular function controlled only at the level of transcription only under positive control in Escherichia coli

1

In a typical bacterial cell, why is the trp operon usually turned "on"? Tryptophan is usually needed for protein synthesis and usually is in low concentrations. Tryptophan is abundant in the diet. Lactose digestion stimulates tryptophan use. Tryptophan is regulated constitutively.

1

In allosteric regulation of an operon, what is not true about the small inducer molecule? It can regulate transcription by binding to the DNA. It can bind to the repressor protein and changes its shape and activity. It can prevent a repressor from binding to the DNA. It can help regulate transcription of the operon.

1

In the lac operon, the inducer ________ binds to the repressor. When it does, the repressor changes shape. The shape change causes the repressor to come off the DNA. This type control over protein function is ______________. lactose; allosteric regulation lactose; constitutive regulation glucose; positive control glucose; negative control

1

The change in the shape of the lac repressor with the binding of lactose is an example of __________. allosteric regulation translational control negative control of transcription positive control of transcription

1

The lactose operon is likely to be transcribed when __________. lactose levels are high within the cell the lactose level in the cell is low there is more glucose than lactose in the environment there is glucose but no lactose in the cell

1

The positive effect of lactose on the expression of the genes required to use lactose is logical because __________. when lactose is present, bacteria need to use it when lactose is absent, bacteria need to make it when lactose is absent, bacteria can use it when lactose is present, bacteria need to make it

1

Transcription of the lac operon is subject to positive control by a catabolite activator protein (CAP). CAP must be bound to which of the following to bind to DNA? cAMP Inducer Activator Repressor

1

Transcriptional control can be negative or positive. ____________ occurs when a regulatory protein prevents _______________. __________ occurs when a regulatory protein increases the frequency of initiating transcription. Negative control; transcription; Positive control Allosteric control; transcription; Positive control Negative control; translation; Positive control Positive control; transcription; Allosteric control

1

What is a potential disadvantage of organizing several genes into an operon Damage or a mutation to the regulatory parts of the operon would prevent the transcription of all of the genes. The structural genes cannot be transcribed individually. All of the enzymes are synthesized in equal amounts. There can only be negative control of the operon's genes.

1

What is the function of the lac operator? To bind the lac repressor, preventing transcription of the lac operon To bind RNA polymerase, initiating transcription of the lac operon To cleave lactose to produce glucose and galactose To transport lactose into the cell, allowing induction of the lac operon

1

What is the function of the lac repressor? To bind the lac operator, preventing transcription of the lac operon To bind the lac promoter, initiating transcription of the lac operon To cleave lactose to produce glucose and galactose To transport lactose into the cell, allowing induction of the lac operon

1

What is the function of the promoter of the lac operon? To bind RNA polymerase, initiating transcription of the lac operon To bind the lac repressor, preventing transcription of the lac operon To cleave lactose to produce glucose and galactose To bind the lac operator, preventing transcription of the lac operon

1

When _______ levels outside of the cell are low, the catabolite activator protein (CAP) forms a complex with cAMP. The CAP-cAMP complex then binds to ____________. glucose; a regulatory sequence in DNA just upstream of the promoter and interacts with RNA polymerase in a way that allows transcription to begin much more frequently lactose; a regulatory sequence in the operator and interacts with RNA polymerase to inhibit translation of a protein glucose; a regulatory sequence region of the repressor resulting in a conformation change, allowing transcription of lac genes to continue lactose; a regulatory sequence in DNA just upstream of the promoter and interacts with RNA polymerase in a way that allows transcription to begin much more frequently

1

When lactose levels are low, which statement is true about the levels of transcription from the lacI gene? lacI transcription is unaffected. There is no lacI transcription. lacI transcription levels decrease. lacI transcription levels increase.

1

Which molecule acts as an inducer of lac operon transcription? Lactose lacI RNA polymerase β-galactosidase

1

Which of the following statements best summarizes how the lac operon is regulated? Positive and negative control elements regulate the lac operon. The lac operon is only under negative control. Positive and negative control elements induce the lac genes. The lac operon is only under positive control.

1

Which regulator of the lac operon is located at some distance away from the main part of the operon? lacI Promoter Operator lacZ, lacY, and lacA

1

Gene expression can be controlled at which of these levels? Translation All of these are correct Post-translation Transcription

2

If a bacterial cell came in contact with milk with fructose dissolved in it, what would happen to the lac operon? Fructose would bind to a catabolite activator protein (CAP) and induce the lac operon. The lac operon would be induced because fructose does not stop activation of the lac operon. Fructose would stop activation of the lac operon. Fructose would bind the lac operon repressor and prevent it from binding to the operator.

2

Negative control of transcription occurs when a(n) __________, a regulatory protein, binds to DNA and shuts down transcription. operon operator repressor activator

3

What effects will growth in glucose and lactose have on Escherichia coli sugar metabolism and gene expression? The bacteria will use lactose as their primary sugar source until it is used up and then switch to glucose. The bacteria will never produce β-galactosidase. The bacteria will always produce β-galactosidase. The bacteria will use glucose as their primary sugar source until it is used up and then switch to lactose.

4

Which of the following describes post-translational control? Post-translational control is particularly important because of its efficiency; it saves the most energy for the cell,because it controls gene expression before the cell expends many resources. Post-translational control occurs when a regulatory protein called an activator binds to DNA and triggers transcription. Post-translational control allows more rapid changes than transcriptional control in the amounts of different proteins because the mRNA has already been made and is available for translation. Post-translational control provides the most rapid response because only one step is needed to activate or inactivate an existing protein.

4

Which of the following experiments would help determine whether the β-galactosidase gene is regulated by lactose or glucose? Measure the amount of β-galactosidase produced by Escherichia coli grown on a lactose plate. Measure the amount of β-galactosidase produced by Escherichia coli grown on a glucose plate. Measure the amount of β-galactosidase produced by Escherichia coli grown on a glucose + lactose plate. Measure the amount of β-galactosidase produced by Escherichia coli grown on a glucose plate, a lactose plate, and a glucose + lactose plate.

4

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

Cells would expend significantly more energy.

What is the pattern of expression of β-galactosidase in lacI— cells and why? View Available Hint(s) No expression, because lactose is absent. Constitutive expression, because the galactoside permease gene is defective Constitutive expression, because there is no repressor No expression, because the β-galactosidase gene is defective

Constitutive expression, because there is no repressor

What is the primary benefit of organizing a group of genes into an operon? The ability to turn genes "on" and "off" Reducing the number of RNA polymerase molecules that are needed Having a group of genes near each other Coordinated and simplified regulation of a group of genes with a common function

Coordinated and simplified regulation of a group of genes with a common function

Which aspect of normal lac operon function is an example of post-translational control? View Available Hint(s) Control of repressor protein synthesis Interaction of lactose with galactoside permease Binding of repressor to the operator Interaction of lactose with the repressor

Interaction of lactose with the repressor

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? It makes molecules that bind to one another. It cannot make a functional repressor. It cannot bind to the inducer. It cannot bind to the operator. It makes a repressor that binds CAP.

It cannot bind to the inducer.

What is the role of lactose in regulating lac operon expression? View Available Hint(s) It represses transcription by binding to the repressor. It induces translation by binding to the repressor and removing it from the mRNA. It induces transcription by binding to the repressor and causing its release from the operator. It induces transcription by binding directly to the promoter and attracting RNA Polymerase.

It induces transcription by binding to the repressor and causing its release from the operator.

High glucose levels decrease activity of the galactoside permease transporter. When lactose and glucose levels are high outside the cell, what will be the effect on lactose transport? See Section 18.3 (Page) . View Available Hint(s) Lactose transport will decrease. Lactose transport will not change. Lactose will not enter the cell, but it will be metabolized outside the cell. Lactose transport will increase.

Lactose transport will decrease.

Which of the following conditions would result in the highest levels of transcription of the lac operon? Low levels of both lactose and glucose in the cell Low levels of glucose and high levels of lactose in the cell High levels of both lactose and glucose in the cell High levels of glucose and low levels of lactose in the cell

Low levels of glucose and high levels of lactose in the cell

On what sequence of DNA does the lac repressor bind? See Section 18.1 (Page) . View Available Hint(s) Operator of lac operon Lac I sequence Promoter of lac operon Lac I promoter

Operator of lac operon

Which mechanism of gene expression regulation is the fastest but most energy demanding of the cell? View Available Hint(s) Post-translational control of the protein activity Translational control Transcriptional control Production of multiple proteins by a single mRNA

Post-translational control of the protein activity

For an operon under negative control to be transcribed, which of the following must occur? RNA polymerase cannot be present, and the repressor must be inactive. RNA polymerase must not occupy the promoter, and the repressor must be inactive. RNA polymerase and the active repressor must be present. RNA polymerase must bind to the promoter, and the repressor must be inactive.

RNA polymerase must bind to the promoter, and the repressor must be inactive.

Which of the following is true when mutant cells containing a mutation that eliminates lacI transcription are grown in high lactose and high glucose? The lac operon will be transcribed at low levels despite the presence of glucose. The lac repressor is constantly bound to the lac operator. Levels of transcription of the lac operon will be very high. Expression from the lac operon will be completely eliminated.

The lac operon will be transcribed at low levels despite the presence of glucose.

According to the lac operon model proposed by Jacob and Monod, what is predicted to occur if the operator is removed from the operon? Galactosidase permease would be produced, but would be incapable of transporting lactose. Only lacZ would be transcribed .Only lacY would be transcribed. The lac operon would be transcribed continuously.

The lac operon would be transcribed continuously.

Why is the lacI mutant a constitutive mutant? The mutant cells require lactose and glucose to induce transcription of lacZ, lacY, and lacA. The mutant cells require glucose to induce transcription of lacZ, lacY, and lacA. The mutant cells require lactose to induce transcription of lacZ, lacY, and lacA. The mutant cells do not need an inducer to express β-galactosidase.

The mutant cells do not need an inducer to express β-galactosidase.

What is the mutant phenotype of bacteria that lack a functional lacY gene? They cleave lactose because there is an abundance in the cell. They do not accumulate lactose inside the cell. They cannot cleave lactose into glucose and galactose. They rapidly cleave lactose in the presence of glucose.

They do not accumulate lactose inside the cell.

Of the three modes of gene regulation shown in Figure 18.1, which is the most efficient in resource use? Post-translational control Transcriptional control Translational control. All three are equally efficient.

Transcriptional control

An operon is ______. View Available Hint(s) a form of operator that is under negative regulation a DNA sequence that is recognized by the repressor protein a form of operator that is under positive regulation a set of bacterial genes that are regulated together and transcribed into a single RNA a bacterial gene that is controlled by a promoter

a set of bacterial genes that are regulated together and transcribed into a single RNA

Which of the following statements is true of regulons? All statements are true. Regulons allow bacteria to respond to challenges that include shortages of nutrients, sudden changes in temperature, exposure to radiation, and shifts in habitat. A regulon is a set of separate genes or operons that contain the same regulatory sequences and that are controlled by a single type of regulatory protein. A regulon can be under negative control by a repressor protein or positive control by an activator protein.

all true

X-gal is a colorless molecule cleaved by β-galactosidase into two products, one of which is blue. Cells with a mutation in the promoter of the lac operon that makes this sequence nonfunctional were plated onto a medium that contains X-gal. What color or colors would the colonies from these cells be? All white All blue Some blue and some white Yellow

all white

An E. coli cell without a functional lacI gene is expected to _____. be unable to transport lactose into the cell always produce β-galactosidase never produce β-galactosidase be unable to metabolize lactose within the cell

always produce β-galactosidase

what does beta galactosidase and galactoside permease do?

beta galactosidase- cleaves lactose into glucose and galactose galactoside permease- allows lactose to get into the cell

Why does the binding of the repressor protein to the operator in an operon stop transcription? The repressor blocks RNA polymerase. The repressor alters the DNA sequence. The RNA polymerase binds to the repressor instead of the promoter. The repressor blocks the RNA polymerase's active site.

block RNA polymerase

inhibition of cap activity

cap activity- positive control glucose levels low outside cell the cAMP is high inside the cell CAP bound to CAP site. stabilizes RNA polymerase. can only bound when they are bound to cAMP cAMP only high when glucose levels low transcription of lac operon high glucose this means low cAMP which means formation of cAMP is inhibited infrequent transcription of lac operon

What is the function of β-galactosidase? To cleave lactose into glucose and galactose To bind the lac repressor and induce the lac operon To bind the lac promoter and initiate transcription of the lac operon To be transported by the galactoside permease out of the cell

cleave lactose

E coli using glucose vs using lactose

glucose: easier to use as a carbon source lactose: harder bc needs more processing (needs to be cleaved into subunits, requires more energy) like to use glucose over lactose. if had a choice, will use glucose every time

The greatest expression of the lac operon occurs when lactose levels are _____. low and glucose levels are low low and glucose levels are high high and glucose levels are high high and glucose levels are low

high and glucose levels are low

inducer exclusion

high concentration of glucose outside the cell means low concentration of lactose inside the cell bc glucose will not let lactose enter. protein binds to operator and no inducer present so stays there preventing transcription low conc glucose and high conc of lactose means lactose can act as inducer

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

inducer

glucose affects lac operon

inducer exclusion and inhibition of cap activator

does E coli produce beta galactosidase when both glucose and lactose present?

just glucose: no glucose and lactose: no lactose: yes

different mutants

lac I mutant- not a functional repressor or no repssor. cannot bind to operon. transcription of lac opern all the time regardless of the carbon source (glucose, lactose, glucose and lactose) lac Z mutant- no beta galactosidase meaning no lactose can be cleaved (regardless is lactose is present) lac Y mutant- no lactose is let into the cell (cannot use lactose as energy source)

In the lac operon, the repressor protein is encoded by which of the following? lacZ lacY lacR lacI

lac i

Which of the following mutants would be predicted to produce β-galactosidase even in the absence of lactose? lacI- lacY- lacZ- lacA-

lacI-

regulation of gene expression most efficient? fastest?

most efficeint: transcriptional control (do not waste all the energy making a protein that is not needed) fastest: post translational control: protein already made, just need a little modification before it's ready to be used

An Escherichia coli cell contains a mutation in the lacI gene such that the encoded protein is able to bind the lac operator but is unable to bind lactose, the inducer. Would the expected transcription of the lacZ and lacY genes increase or decrease or have no change when this cell is exposed to high levels of lactose? No change in transcription of both genes Increase in transcription of both genes Decrease in transcription of both genes Increase in transcription for lacZ but no change of transcription for lacY

no change

The presence of a mutant lac repressor that could not bind lactose would result in _______ transcription even when lactose was present because the mutant repressor would remain bound to the lac __________ See Section 18.3 (Page) . View Available Hint(s) no; promoter no; operator lots of; promoter lots of; operator

no; operator

The lac repressor protein binds to the operator when it is ______. View Available Hint(s) bound to arabinose bound to glucose not bound to lactose not bound to glucose bound to lactose

not bound to lactose

A(n) _______________ is a piece of DNA with a group of genes that are transcribed together as a unit. operon promoter repressor operator

operon

The lac operon contains three structural genes that are transcribed and translated: lacZ, lacY, and lacA. Two of the proteins are directly tied to lactose metabolism: galactoside permease and β-galactosidase. What do these two enzymes do?

permease-transport lactose into cell beta-cleaves lactose

During transcription of the lac operon, the catabolite activator protein (CAP) provides what type of control? Positive control Negative control Allosteric regulation Global gene regulation

pos control

In bacteria, the flow of information from DNA to a final active protein product occurs in three steps, represented by arrows in the following pathway: DNA → mRNA → protein → activated protein Gene expression can be controlled at any of these steps: transcriptional control, translation control, or post-translational control. Among these mechanisms of gene regulation, there is a clear trade-off among the speed of response and the conservation of nucleotides, amino acids, energy, and other resources. __________ provides the fastest response, whereas ___________ conserves resources the most.

post trans; transcriptional

negative control of the lac operon

regulated using the Lac I gene. usually codes for a regulatory protein which binds to the promoter and prevents transcription

In negative control, a gene is switched off when _____. a kinase adds a phosphate to DNA lactose is transported into the cell a regulatory protein binds to DNA and shuts down transcription a regulatory protein is removed from DNA and shuts down transcription

regulatory protein binds to DNA and shuts down transcription

positive control

regulatory protein stabilizes RNA polymerase at promoter and enables it to engage with promoter more consistnelty, increasing transcription of the gene

Regulons can work through negative control using __________ and positive control using __________. activators; inducers repressors; activators activators; repressors inducers; activators

repressors; activators

operon

series of genes close together. transcribed together and also involve in same process

Suppose you analyze the protein-coding sequence of the lacZ and lacY genes of cells from the three mutant colonies and find that these sequences are wild type (normal). What other region of the lac operon might be altered to account for the mutant phenotype of these colonies? the lac promoter the repressor the inducer the lacI gene

the lac promoter

The product of the lacI gene is _____. β-galactosidase a transport protein embedded within the membrane the repressor an enzyme

the repressor

Which type of regulation is not involved in normal induction of the lac operon by lactose? Translational control Negative control of transcription Allosteric regulation Positive control of transcription

trans control

Genes that are transcribed constitutively are said to be __________. transcribed at overexpressed levels transcribed only as needed transcribed at basal levels transcribed all the time

transcribed all the time

What is the co-repressor in the trp operon? Lactose Tryptophan Glucose cAMP

trp

The trp operon regulates the synthesis of the amino acid tryptophan. When tryptophan concentrations are high, __________ binds to the repressor protein and activates it. The repressor attaches to the operator and blocks transcription of the trp genes. This regulation is a type of ______________, a form of control in which the final product of a pathway inhibits the production of the product. tryptophan; negative feedback glucose; allosteric regulation tryptophan, positive feedback glucose; negative feedback

trp; neg feedback

trp operon (negative control0

tryptophan is present, transcription is blocked. acts as a corepressor allowing for the repressor protein to stay bound to the operator (no transcription) trp not present, repressor cannot bind to operator so transcription ensues feedback inhibition cells do not want to produce enzymes needed to make trp if it is already present in the cell to prevent the cell from constantly producing enzymes it does not need as trp levels decrease, does not bind to repressor as frequently so transcription ensues (cell needs more trp) high levels means trp can act as the co repressor to prevent transcription bc cells already has all the trp it needs

negative control (more in depth)

when lactose not present, protein binds to operator and stops transcription when lactose is present, acts as an inducer and causes the operator to change shape and fall off the operator, which allows for transcription of the lac operon