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