Genetics Ch14

The lac repressor is composed of how many identical subunits?

4

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.

Monod and Jacob studies lactose metabolism in ____ _______

E. coli

Unregulated genes are also called _______ genes

constitutive

The lac repressor functions as a homotetramer, a protein composed of ________ subunits.

four identical

The locA gene encodes the enzyme ________

galactoside transacetylase

Monod, Jacob, and Pardee identified rare E. coli mutants that ________

had abnormal lactose adaptations

A regulatory protein that inhibits translation is called a __________ _________

translational repressor

What genes are in the trp operon?

trpA, trpB, trpC, trpD, 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

When the lac repressor binds to the operator region, it must bind to _______________ sites (a number) within the operator to inhibit transcription of the lac operon genes.

two

When both lactose and glucose are absent ... (select all that apply) -lac operon transcription rate is very high -CAP is bound to the DNA -lac repressor does not bind to the operator -lac repressor is bound to the operator -CAP does not bind to DNA -lac operon transcription rate is very low

-CAP is bound to the DNA -lac repressor is bound to the operator -lac operon transcription rate is very low

Which two hypotheses regarding constitutive synthesis of the lac operon did Jacob, Monod and Pardee test by using merozygotes? (select all that apply) -The lacI- mutation resulted in the synthesis of an internal activator. -The lacI- mutation eliminated the function of the lac repressor. -The lacI- mutation eliminated repressor-binding sequences on the operator. -The lacI- mutation removed sequences in the lac operon promoter.

-The lacI- mutation resulted in the synthesis of an internal activator. -The lacI- mutation eliminated the function of the lac repressor.

Exposure of bacterial cells to lactose increases levels of lactose-utilizing enzymes ______.

1,000- to 10,000-fold

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

3

Why is the transcription rate of the lac operon low when both glucose and lactose are absent?

Lac repressor blocks transcription by binding to the operator region.

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

a single promoter

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

a trans-acting factor

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

activator

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

allolactose

LacIS mutations would result in a lac operon that is ______

always repressed

When tryptophan levels are high, tryptophan binds to trp repressor protein causing a conformational change that in turn causes the trp repressor to ___________

bind to the operator site

T/F: The rate of transcription initiation rarely influences overall gene expression

false

The term ___________ regulation refers to control of proteins already present in the cell.

posttranslational

The corepressor for a repressible operon may be _________

the product of that operon

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

the rate at which transcription is initiated

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

three

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

tran-acting factor

Genetic control of the production of specific proteins at specific times would occur in which of the following situations? (select all that apply) -When a bacterial cell encounters a toxin in the environment -Producing enzymes to metabolize specific sugars when those sugars are found in the environment -When bacterial cells are getting ready to divide -When bacteria are subject to heat stress -Producing the proteins needed to assemble ribosomes

-Producing enzymes to metabolize specific sugars when those sugars are found in the environment -When bacterial cells are getting ready to divide -When bacteria are subject to heat stress

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.

How do a corepressor and an inhibitor differ?

A corepressor binds to a repressor protein, while an inhibitor binds to an activator protein.

T/F: Gene expression is always the same

False

How does the product of the micF gene regulate the expression of the ompF gene?

The binding of the micF RNA prevents translation of the ompF mRNA.

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.

An enzyme may contain two sites: a catalytic site, and a regulatory or ______________ site.

allosteric

When bound to operator, the lac repressor ______.

allows very small amounts of the lac enzymes to be made

The RNA transcribed from the micF gene is complementary to the ompF mRNA and acts as a(n) ________________strand.

antisense

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

cannot transcribe

High levels of ______ allow(s) transcription of the trpL mRNA to progress to its stop codon.

charged tRNA^(Trp) molecules

In the coupling of transcription and translation, the ribosome pauses at specific codons in the trpL mRNA because the amounts of ______.

charged tRNA^(Trp) molecules are low

Antisense RNA is an RNA strand that is ________________ to an mRNA molecule.

complementary

In the trp operon, tryptophan acts as a(n) ______.

corepressor

In the trp operon, the attenuator DNA ________

does not encode an enzyme

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 product of the biosynthetic activities of the enzymes from an operon may act as a(n) ______________ if the operon is repressible.

inhibitor/corepressor

In feedback inhibition, the final product in a metabolic pathway _____________

inhibits an enzyme that acts early in the pathway

In the attenuation process, formation of the 3-4 stem loop from the trpL gene transcript in combination with a U-rich region results in ________________ termination, also known as ______________-dependent termination.

intrinsic; rho

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 protein binds to _________

mRNA near the start codon

A translational repressor recognizes sequences within __________ and __________ translation.

mRNA; inhibits

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

Certain proteins help a bacterium survive environmental stress such as heat shock. These proteins are required _______

only when confronted with the stress

Certain proteins help a bacterium survive environmental stress such as heat shock. These proteins are required ________

only when confronted with the stress

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

Phosphorylation, acetylation, and methylation are all types of _________

posttranslational covalent modifications

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

promoter

During attenuation, intrinsic termination of the trpL gene transcript occurs due to a U-rich region combined with a stem-loop structure formed between ______.

region 3 and region 4

In postranslational regulation, the final product of a metabolic pathway may bind to the ____________ site of an enzyme and inhibit its catalytic ability.

regulatory/allosteric

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

repressible; inducible

A translational repressor protein may bind to the mRNA and ____________

stabilize a secondary structure that prevents translation

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

attenuation

T/F: Gene regulation is constant

false

Constitutive genes ____

are unregulated

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

cis-acting

Genetic control of the production of specific proteins at specific times would occur in which of the following situations? (select all that apply) -Producing the proteins needed to assemble ribosomes -Producing enzymes to metabolize specific sugars when those sugars are found in the environment -When bacteria are subject to heat stress -When bacterial cells are getting ready to divide -When a bacterial cell encounters a toxin in the environment

-Producing enzymes to metabolize specific sugars when those sugars are found in the environment -When bacteria are subject to heat stress -When bacterial cells are getting ready to divide

Why is transcription of the lac operon low when both lactose and glucose are present?

The low levels of cAMP result in CAP not binding to the CAP site.

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

allactose; cAMP

Unregulated genes have ______

constant levels of expression

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

decrease

The genes in the trp operon encode ______.

enzymes used in tryptophan biosynthesis

Monod, Jacob, and Pardee studied an E. coli strain with a lacI- mutation in which the lac operon was expressed ________

even in the absence of glucose

T/F: Effector molecules influence gene expression by binding to DNA

false

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

glucose; galactose

When the repressor is not bound to allolactose, the cAMP-CAP complex helps form a DNA __________ to which repressor protein binds.

loop

In the absence of allolactose, the cAMP-CAP complex assists lac repressor by forming a ______.

loop including O1 and O3

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

merozygote (partial diploid)

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

negative

In an E. coli cell, when tryptophan levels are low ______ (select all that apply) -products of the trpE, trpD, trpC, trpB, and trpA genes will not be made -attenuation will occur -trp repressor cannot bind to the operator site -trpE, trpD, trpC, trpB, and trp A genes will be transcribed -trp repressor binds to the operator site

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

T/F: The lac repressor does not completely inhibit transcription of the lacZ, lacY, and lacA genes.

True

The product of the lacY gene is required for ______.

active transport of lactose into the bacteria cell

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

adenylyl cyclase

constitutive genes encode proteins the cell needs __________

all the time

The Lac repressor protein binds to the operator and ______.

blocks transcription

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

catabolite repression

The sequential use of sugars by a bacterial cell is called__________

diauxic growth

Examples of a(n) ______________ stress that might require a bacterium to produce a specific protein include osmotic shock or heat shock.

environmental

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

enzyme adaption

When both lactose and glucose are absent, concentrations of cAMP 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

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 attenuation, transcription ________

is stopped prematurely

The ______ gene encodes a repressor protein.

lacI

The enzyme β-galactosidase is encoded by which gene?

lacZ

The three protein-encoding genes in the lac operon are ___________, ___________, and ___________.

lacZ, lacY, and lacA

Monod and Jacob studied _______________ metabolism in E. coli.

lactose

The exposure of bacterial cells to _____________ increases the levels of lactose-utilizing enzymes 100- to 10,000-fold.

lactose

Control of gene expression leads to the production of specific proteins to assist bacterial cells in responses to environmental stressors, preparation for cell division, and _________

metabolism

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

repressor

A corepressor is a small molecule that binds to a _________________ protein, thereby causing the protein to bind to the DNA, while an inhibitor binds to an _________ protein and prevents it from binding to the DNA.

repressor; activator

An inducer could bind to a(n) ______ and prevent it from binding to the DNA, or it could bind to a(n) ______ and cause it to bind to the DNA.

repressor; activator

Jacob, Monod and Pardee formulated alternative hypotheses to explain the constitutive synthesis caused by the lacI- mutation. They proposed that the mutation either eliminated the function of the ________________ or that an internal ________________ was produced.

repressor; activator

The CAP site and the operator site are __________ that function in gene regulation

short DNA segments

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

The lacA gene encodes galactoside transacetylase, an enzyme that covalently modifies ______.

lactose

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

Transcription begins but terminates before the entire mRNA is made during __________

attenuation

Who discovered attenuation by studying the trp operon? Specifically, studying the lack of transcription of the trp operon in the absence of the trp repressor

Charles Yanofsky

A conformational change that prevents the lac repressor from binding to the lac operator occurs when ______________ binds to the lac repressor.

allolactose

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

allolactose

Control of gene expression leads to the production of specific proteins to assist bacterial cells in responses to environmental stressors, preparation for cell division, and ________

metabolism

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

prevents the cell from wasting energy

Transcription regulation by an activator protein is considered to be __________ control

positive

The binding of a small effector molecule to a regulatory protein changes the _______ , of the regulatory protein, which alters its DNA-binding ability

conformation

T/F: A benefit of gene regulation is that encoded proteins will not be produces when they are not needed

True

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

lac

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

positive

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

constitutive genes

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

regulation

Allolactose molecules bind to regulatory sites on the lac repressor protein called _______________ sites that differ from the region of the repressor that binds the operator.

allosteric

β-ONPG can be used to detect levels of β-galactosidase, because β-galactosidase cleaves β-ONPG into a substance with a _________ color.

yellow

The binding of the allolactose inducer to the lac repressor occurs at a(n) ______ site.

allosteric

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