Chapter 14 Gene Regulation in Bacteria

In the trpL mRNA,______stem-loops are possible.

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.

Would using a merozygote better indicate regulation of a gene by a trans-acting factor or a cis-acting element?

A trans-acting factor

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.

What do you call an RNA strand that is complementary to an mRNA molecule?

Antisense RNA

Who discovered attenuation by studying the trp operon?

Charles Yanofsky

What type of genes encode proteins the bacterial cell needs all the time?

Constitutive genes

True or false: Effector molecules influence gene expression by binding to DNA.

False

True or false: Gene expression is always the same.

False

True or false: Gene regulation is constant.

False

True or false: The rate of transcription initiation rarely influences overall gene expression.

False

The enzyme β-galactosidase is encoded by which gene?

LacZ

What is the name for a strain of bacteria containing an F' factor?

Merozygote

Can a particular segment of mRNA from the trp operon participate in the formation of more than one stem loop at the same time?

No

How does an effector molecule influence gene expression?

The effector molecule binds to a regulatory protein and affects its ability to bind DNA.

Why does transcription of the trp operon continue when tryptophan levels are low?

The ribosome pauses in region 1, preventing the 3-4 stem-loop from forming.

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

Trans-acting factor

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

True

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

a single promoter

A regulatory protein that increases the rate of transcription is a(n)

activator

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

adenylyl cyclase

Constitutive genes encode proteins the cell needs ______.

all the time

A conformational change that prevents the lac repressor from binding to the lac operator occurs when_____binds to the lac repressor.

allolactose

The binding of ______ to the lac repressor promotes a conformational change that prevents the repressor from binding to the lac operator.

allolactose

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

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

cAMP

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

cannot transcribe

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 ______________-_____________element.

cis acting

Antisense RNA is an RNA strand that is_____to an mRNA molecule.

complementary

Unregulated genes have ______

constant levels of expression.

Unregulated genes are also called ____ genes.

constitutive

Posttranslational regulation refers to ______.

control of proteins already in the cell

Many bacterial species use sugars sequentially. This is called ______

diauxic growth

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 research of Monod and Jacob that led to the initial understanding of gene regulation stemmed from an interest in ______.

enzyme adaptation

In catabolite repression, transcription is influenced by the presence of _____.

glucose

The enzyme beta-galactosidase cleaves the sugar lactose into

glucose galactose

The transport of ______ into a cell causes a _______ in the concentration of cyclic-AMP by inhibiting adenylate cyclase.

glucose; decrease

When both lactose and glucose are absent, concentrations of cAMP are ______.

high

When four molecules of allolactose are bound to lac repressor, and repressor can no longer bind to operator, and RNA polymerase is free to transcribe the operon, the operon has been

induced

When lactose is depleted from the environment, the ______.

intracellular concentration of allolactose falls

In the trpL sequence, the 3-4 stem-loop together with the U-rich attenuator sequence acts as a(n)

intrinsic, sequence

In attenuation, transcription ______.

is stopped prematurely

Select all of the following that are protein-encoding genes in the lac operon.

lacA lacZ lacY

The ______ gene encodes a repressor protein.

lacI

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 lacY gene encodes lactose_______ a membrane protein.

permease

An operon encodes a mRNA, an RNA that contains the sequences of two or more genes.

polycistronic

Transcription regulation by an activator protein is considered to be ______ control.

positive

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

regulation

Anabolic enzymes are usually encoded by ______ operons, and ______ operons usually encode catabolic enzymes

repressible; inducible

A regulatory protein that binds to DNA and inhibits transcription is a(n)

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

The conversion of a riboswitch form one conformation to another is due to ______.

the binding of a small molecule

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

the rate of transcription initiation

When only lactose is present in bacterial cells, levels of the effector molecules______and___________

allolactose,cAMP

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

Constitutive genes ______.

are unregulated.

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

attenuation

The trp operon is regulated by a repressor protein and by_____in which transcription is stopped prematurely.

attenuation

Transcription begins but terminates before the entire mRNA is made during

attenuation

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 genes in the trp operon encode ______.

enzymes used in tryptophan biosynthesis

When the product of a gene produced in a metabolic pathway inhibits an enzyme that acts early on in the pathway it is called

feedback inhibition

The mRNA made from the trpL gene has four regions that can ______.

form stem-loops

The three protein-encoding genes in the lac operon are

lacZ, lacY, lacA

When only ______ is present, allolactose and cAMP levels are high.

lactose

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

A translational repressor recognizes sequences within ______ and ______ translation.

mRNA; inhibits

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

merozygote

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

negative

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

negative

A polycistronic mRNA contains the sequence(s) ______.

of two or more genes

In the thi operon, when levels of TPP are low, the mRNA folds into a stem-loop structure that ______.

prevents formation of the terminator stem-loop

Allolactose is a small effector molecule that binds to the lac repressor and ______.

prevents repressor from binding to DNA

In an operon, the ______ signals the beginning of transcription.

promoter

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

promoter, terminator

The product of the lacY gene is required for ______.

the transport of lactose into the bacterial cell

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

the trp leader peptide

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

three

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

transcribes the operon

Riboswitches can regulate ______.

transcription or translation

The TPP riboswitch in E. coli controls____whereas the TPP riboswitch in B. subtilis controls

translation transcription

A regulatory protein that inhibits translation is called a

translational repressor

Select the genes in the trp operon.

trpD trpB trpC trpA trpE

The mRNA made from the ______ gene contains codons for 14 amino acids that form the trp leader peptide.

trpL

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

trpL