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
