Chapter 14

How many binding sites are there in the lac operon for the lac repressor?

3

In the trpL mRNA, ------- stem-loops are possible.

3

Studies indicate that the lac operon has ______ operator site(s) for the lac repressor.

3

In the trpL gene, which stem-loop together with the U-rich attenuator sequence acts as an intrinsic terminator?

3-4

Why is a merozygote better at complementing a mutation in a trans-acting factor than in a cis-acting element?

A cis-acting element must be adjacent to the gene it is regulating.

What happens when levels of allolactose rise inside an E. coli cell?

Allolactose binds to the lac repressor and prevents it from binding to the operator.

How can antisense RNA inhibit translation?

An antisense RNA binds to a transcript and inhibits translation.

T/F: An inducer binds to an activator protein and inhibits transcription.

False

T/F: An inhibitor regulates an inducible gene.

False

T/F: The CAP protein is an activator that binds to the operator.

False

T/F: The structural proteins encoded by the lac operon are involved in lactose synthesis.

False

T/F: When both glucose and lactose are absent, transcription of the lac operon occurs.

False

If a cell has a mutation in the lacY gene that produces a non-functional product, how is regulation of the lac operon affected?

The lac operon cannot be induced, because lactose cannot enter the cell. (lacY gene encodes lactose pernease which is required for active transport of lactose into the cytoplasm of the bacterium)

T/F: The presence of a small effector molecule may inhibit transcription.

True

T/F: The product of LacI is an allosteric protein that can undergo a conformational change when allolactose binds to it.

True

Cyclic-AMP is a small effector molecule produced by the enzyme

adenylyl cyclase

When bound to operator, the lac repressor ______

allows very small amounts of the lac enzymes to be made

In the thi operon, when levels of TPP are low, the 5' end of the mRNA forms an --------- stem-loop structure that allows transcription to continue.

antiterminator

When the lac repressor is bound to the operator, RNA polymerase ______ the lacZ, lacY, or lacA genes.

cannot transcribe

Inducible operons usually encode ______ enzymes, and repressible operons usually encode ______ enzymes.

catabolic; anabolic

The genes in the trp operon encode ______.

enzymes used in tryptophan biosynthesis

A strain of bacteria containing F' factor genes is called a---------- or a partial diploid.

merozygote

A polycistronic mRNA contains the sequence(s) _____

of two or more genes

It has been shown that the lac operon has three ------- sites to which the lac repressor can bind.

operator

When the lac repressor binds to the lac --------site, RNA polymerase cannot transcribe the lacZ, lacY or lacA genes.

operator

A(n)--------- is a group of two or more genes under the transcriptional control of a single promoter.

operon

The research of Jacob and Monod provided ______.

our initial understanding of gene regulation

The mRNA made form the trpL gene contains codons for 14 amino acids that form ______.

the trp leader peptide

Riboswitches can regulate ______.

transcription or translation

A regulatory protein that inhibits translation is called a

translational repressor

Select the genes in the trp operon

trpC trpA trpD trpE trpB

In an E. coli cell, when tryptophan levels are low ______

- trpE, trpD, trpC, trpB, and trp A genes will be transcribed - trp repressor cannot bind to the operator site

Transcription of the lac operon results in the production of how many different mRNA transcripts?

1

How is the lac operon regulated?

It is inducible under negative and positive control

Which combination of two operator sites have the lowest amount of repression?

O2 and O3

Determine if it describes regulation at the transcription, translation or post-translation level: A protein is covalently modified.

Posttranslation

Determine if it describes regulation at the transcription, translation or post-translation level: The product of a metabolic pathway inhibits the first enzyme in a pathway.

Posttranslation

How would the interpretation of the Jacob, Monod, and Pardee experimental results change if lacO was mutated instead of lacI?

The lac operon has constitutive expression and O has a cis-effect

How will transcription of the lac operon be affected by a mutation in the lacI gene that results in an inability to synthesize any repressor protein or produces a repressor protein that is unable to bind to the operator?

The operon cannot be repressed.

You identify a strain of bacteria that has a mutated trp operator that cannot bind the repressor. Under what circumstances will the trp operon be transcribed?

The trp operon will be transcribed when levels of tryptophan in the cell are low.

What type of regulatory element does not need to be adjacent to the gene(s) it is regulating?

Trans-acting factor

Determine if it describes regulation at the transcription, translation or post-translation level: A transcription terminator forms in the RNA.

Transcription

Determine if it describes regulation at the transcription, translation or post-translation level: Genetic regulatory proteins bind to the DNA.

Transcription

In Bacilus subtilis, a riboswitch controls the ___ of the thi operon involved in thiamin pyrophosphate synthesis.

Transcription

T/F: The LacI gene makes a repressor protein.

True

T/F: The lac repressor protein is active in the absence of lactose within the cell.

True

True or false: The lac repressor does not completely inhibit transcription of the lacZ, lacY, and lacA genes.

True

Attenuation of the trp operon requires which conditions to be met?

Tryptophan levels must be high, and regions 3 and 4 must pair.

An operon is a group of two or more genes under the transcriptional control of ______.

a single promoter

The transport of glucose into a bacterial cell causes the intracellular level of cyclic-AMP to fall because the enzyme ------- is inhibited

adenylyl cyclase

The intracellular concentration of the inducer remains high as long as lactose is available in the environment.

allolactose

The lac repressor is inactivated by binding to which of the following?

allolactose

The small effector molecule ------- prevents the lac repressor from binding to the operator site.

allolactose

When only lactose is present in bacterial cells, levels of the effector molecules ---- and ---- are high

allolactose; cAMP

The binding of a small effector molecule to a regulatory molecule alters the regulatory protein's conformation, and that ______.

alters the protein's ability to bind to DNA

LacIS mutations would result in a lac operon that is _______

always repressed

The absence of lactose results in the lac repressor protein ____.

binding to the DNA

The lac repressor

binds to the operator and prevents transcription of the lactose operon.

The Lac repressor protein binds to the operator and ______.

blocks transcription

During attenuation, transcription begins, ______.

but it is terminated before the entire mRNA is made

The small effector molecule produced by the enzyme adenylyl cyclase is ______

cAMP

The somewhat imprecise term that describes how transcriptional regulation is influenced by glucose is

catabolite repression

A DNA segment that must be adjacent to the gene(s) it regulates is a

cis acting

Unregulated genes have ______

constant levels of expression.

Posttranslational regulation refers to ______.

control of proteins already in the cell

The enzyme beta-galactosidase cleaves the sugar lactose into ----- and ------

galactose, and glucose

The repressor is bound to the operator when tryptophan levels are ...

high

When tryptophan levels are low, the transcription of the trp operon will occur at a ______ rate because ______.

high; the trp repressor cannot bind to the operator site.

An inducer is a small effector molecule that causes transcription to ______.

increase

he attenuator is similar to rho ___ termination.

independent

In feedback inhibition, the final product in a metabolic pathway ______.

inhibits an enzyme that acts early in the pathway

When lactose is depleted from the environment, the ______.

intracellular concentration of allolactose falls

In attenuation, transcription ______.

is stopped prematurely

Jacob, Monod, and Pardee isolated bacteria with mutations that resulted in the constitutive expression of the ------- operon even in the absence of lactose.

lac

Which gene is responsible for producing the protein that converts lactose to allolactose?

lacZ

The three protein-encoding genes in the lac operon are

lacZ, lacY, lacA

When the tryptophan level in the cell is ______, the ribosome pauses in region one of the trpL mRNA, causing region 2 to to bind to region 3 and transcription to continue.

low

The cAMP-CAP binding site is between operators O1 and O3. When cAMP-CAP is bound it facilitates binding of the repressor. Under what conditions would this occur?

low glucose and low lactose

What combination of glucose and lactose would result in high levels of gene transcription from the lac operon?

low glucose, high lactose

The operon is flanked by a(n) ----------that signals the beginning of transcription and a(n) --------- that signals the end of transcription.

promoter, terminator

Which of the following would not be considered a reversible posttranslational modification?

proteolytic processing

The phenomenon in which the level of gene expression can vary under different conditions is gene

regulation

The trpR gene encodes a ...

repressor

As levels of allolactose increase within an E. coli cell, allolactose binds to the lac ---------, promoting a conformational change that prevents binding to the -------site on the DNA.

repressor, operator

An RNA molecule that can exist in two different secondary conformations and thereby affect gene regulation is known as a(n

riboswitch

One form of gene expression control found frequently in prokaryotes involves a ___, which occurs when an RNA can exist in two different secondary conformations.

riboswitch

One conformation of the RNA requires a small molecule binding which stabilizes the ____ structure.

secondary

In bacteria, the most common way to regulate gene expression is by influencing ______.

the rate of transcription initiation

The RNA forms stem loops as it is being...

transcribed

When four molecules of allolactose are bound to the lac repressor, the lac operon is induced, and RNA polymerase ______.

transcribes the operon

Determine if it describes regulation at the transcription, translation or post-translation level:Antisense RNA binds to the mRNA.

Translation

Determine if it describes regulation at the transcription, translation or post-translation level:Repressor proteins bind to an mRNA and prevent ribosome binding.

Translation

Determine if it describes regulation at the transcription, translation or post-translation level:Riboswitches produce an RNA conformation that prevents ribosome binding.

Translation

The trp operon is also regulated by ___ attenuation.

transcription

When both glucose and lactose are present

transcription of the lactose operon is turned off.

Riboswitches can regulate transcription, ___ , and RNA stability.

translation

Translation of mRNA transcribed from the trp operon can be regulated by formation of a secondary structure within the mRNA. The mRNA that forms this secondary structure is transcribed from which gene in the trp operon?

trpL

When attenuation occurs, the mRNA from the trp operon is made as a short piece that terminates shortly past the _____ gene

trpL

The lac repressor is composed of how many identical subunits?

4

Bacteria use riboswitches extensively; about ___ of bacterial genes are regulated this way.

4%

Put the following in order: 1-CAP site, 2-lacZ, 3-lacY, 4-lac operon, 5-lacI, 6-i promoter, 7-lacO, 8-lac promoter, 9-lacA

6,9,1,8,7,4,2,3,9

Which of the following is not part of the lac operon?

lacI

A protein such as a repressor that inhibits transcription is exerting ---------- control of transcription.

negative

By studying the lack of transcription of the trp operon in the absence of the trp repressor, Charles Yanofsky discovered

attenuation

The sequential use of sugars by a bacterial cell is called

diauxic growth

In the trp operon, the attenuator DNA ______.

does not encode an enzyme

The lac repressor binds to what site within the lac operon?

lacO

T/F: CAP binding causes the DNA to bend facilitating RNA polymerase binding.

True

T/F: In the absence of glucose and presence of lactose, allolactose combines with the repressor and allows RNA polymerase to proceed with transcription.

True

T/F: Polycistronic mRNA is transcribed from the lac operon when lactose is present in the cell.

True

When glucose is present ...

cyclic AMP is low, CAP does not bind to the activator binding site, and transcription of the lactose operon is turned off.

A benefit of gene regulation is that encoded proteins are not made when they are not needed. This ______.

prevents the cell from wasting energy