Chapter 18: Gene Regulation in Prokaryotes
Each subunit of the Lac repressor protein contains _______domains.
3
The RNA leader sequence is a region at the _______.
5' end of the mRNA which is untranslated
The lac operon genes are transcribed together in what order?
5'-lacZ-lacY-lacA-3'
When purified, the Lac repressor is ______.
A dimer or tetramer
The product of the lacA gene adds groups to lactose and other sugars.
Acetyl
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 inducer of the genes for lactose utilization is a molecule called
Allolactose
In the trp operon, the interaction between the translation machinery and a portion of the RNA leader called _________the determines whether or not transcription will terminate prematurely.
Attenuators
The lac operon contains three genes; lacZ, which encodes ______-,_______ lacY, which encodes Lac ________, and lacA, which encodes an enzyme called .
Beta-galactosidase; permease; transacetylace
What effect would either a loss-of-function mutation in the lacI gene or a mutation in the operator that prevents repressor binding have?
Both result in constitutive expression of the lac operon.
Breakdown of sugars occurs via ______ pathways, whereas the synthesis of amino acids occurs via ______ pathways.
Catabolic; anabolic
A strain of E. coli that has a mutation in the lacI gene such that the lac operon is expressed even in the absence of lactose, is a(n) _____________mutant.
Constitutive
An cis-acting element is typically a ______.
DNA segment that can influence only the expression of adjacent genes
The lacIs allele is ______ to lacI+ in ______.
Dominant; trans
What happens when tryptophan is removed from the medium in which a trpR— mutant is growing?
Expression of the trp genes increases about three-fold.
In order to use lacZ as a reporter gene, scientists use recombinant DNA technology to create a __________gene which contains the coding region of lacZ and the cis-acting regulatory regions of a different gene.
Fusion
If given a choice of sugars, E. coli prefers
Glucose
The DNA-binding domain of the Lac repressor protein has a characteristic three dimensional structure known as the __________-_________- ________motif.
Helix turn helix
The addition of lactose to a bacterial medium causes a 1000-fold increase in the synthesis of the two proteins Lac permease and β-galactosidase. This phenomenon is termed _______.
Induction
What is the function of the operator site in the lac operon?
It serves as a binding site for the repressor.
Which of the following proteins may function as a dimer or tetramer?
Lac repressor
The product of which gene is not required for the breakdown of lactose?
LacA
The lacA gene encodes a transacetylase, enzyme that covalently modifies _____.
Lactose
Bacterial mRNAs always begin with a region that is not translated. This 5' untranslated region (5' UTR) is also referred to as the RNA
Leader sequence
The inhibition of RNA polymerase activity is termed __________regulation, whereas the enhancement of RNA polymerase activity is known as _________regulation.
Negative; Positive
In the lac operon, the repressor binds to a DNA sequence called the __________site. This site is near the lac promoter.
Operator
A loss-of-function mutation in the lacI gene can have the same effect as a mutation in the _______.
Operator site
Because there is an overlap between the sequences of the lac _______and lac _________ binding of the repressor to the DNA will inhibit RNA polymerase from binding. As a result, the expression of the lac operon genes is blocked.
Operator; promoter
A(n) ________is a group of two or more genes under the transcriptional control of a single promoter.
Operon
Which of the following are regulatory DNA elements of the lac operon?
Promoter and Operator
The DNase I footprinting technique is used to show ________where bind to ______
Protein; DNA/RNA
Bacteria can adjust their behavior according to their population density by using a communication system called
Quorum sensing
______ is a bacterial communication system that allows them to adjust their behavior according to their population density.
Quorum sensing
The enzyme that transcribes a gene's DNA into RNA is called
RNA polymerase
Transcription is the work of ______.
RNA polymerase
To initiate translation, ribosomes attach to the mRNA at a site called the
Ribosome binding site
An RNA leader whose secondary structure, and thus its effect on gene expression, is determined by whether or not it's bound to a small molecule effector is called a(n)
Riboswitch
In attenuation, the level of an amino acid governs the conformation of the leader indirectly. However, leaders that act as _________ change conformation by binding a particular effector directly.
Riboswitches
In the trp RNA leader sequence, the 3-4 stem-loop configuration is called ________ a because it leads to the production of a short, "attenuated" RNA.
Terminator
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. Reason: The ribosome stops at the trp codons in the trp mRNA because it is waiting for charged tRNATrp.
What determines the DNA binding specificity of a protein with a helix-turn-helix motif?
The sequences of amino acids in the helices
A protein that can diffuse through the cytoplasm and act at DNA target sites elsewhere in the genome is called a _________ -acting element
Trans
The product of the lacI gene is a(n) _____________-acting protein that can bind to the __________of a lac operon regardless of its chromosomal location.
Trans; operator
Of the three proteins encoded by genes of the lac operon, the enzyme ___________is not required for the breakdown of lactose.
Transacetylase
During gene expression, the information in DNA is _________ into RNA, and then the mRNA message is ___________ into a polypeptide.
Transcribes; translates
An operon is a group of two or more genes under the transcriptional control of ______.
a single promoter
An effector is a small molecule that _____.
binds to a protein and changes its conformation
The Lac repressor protein binds to the operator and ______.
blocks transcription
The positive regulator of the lac operon is the ________ __________protein (CRP).
cAMP receptor
Positive control of the lac operon involves a small nucleotide known as _________which binds to a protein called ________. The binding of the nucleotide enables the protein to bind to DNA in the regulatory region of the lac operon. This binding increases the ability of ____________to transcribe lac genes.
cAMP; CRP; RNA polymerase
The somewhat imprecise term that describes how transcriptional regulation is influenced by glucose is
catabolite repression
A mutation in the operator that renders it nonfunctional will cause the ______.
constitutive expression of the lac operon
Cyclic AMP is a(n) ______.
effector molecule that is involved in the positive control of the lac operon
Positive regulation and negative regulation typically refer to mechanisms that _____.
enhance or inhibit RNA polymerase activity, respectively
The genes in the trp operon encode ______.
enzymes used in tryptophan biosynthesis
If the transcription of the trp operon is regulated by the action of the the repressor (TrpR) only, we would expect a trpR— mutant to ______
exhibit constitutive expression of the trp genes at the same level regardless of the presence of tryptophan in the medium
The cAMP receptor protein (CRP) _______ of the lac operon.
functions as an activator
The synthesis of RNAs and proteins according to the instructions encoded in DNA is a process called ______.
gene expression
In catabolite repression, transcription is influenced by the presence of _____.
glucose
If E. coli is grown in a medium containing both glucose and lactose, it will use _____.
glucose first until it is depleted, and then lactose
The transport of ______ into a cell causes a(n) _______ in the concentration of cyclic-AMP by inhibiting adenylate cyclase.
glucose, a decrease
Allolactose is ______ of the lac operon.
inducer
The process by which a specific molecule stimulates synthesis of a given protein is called
induction
In attenuation, transcription ______.
is stopped prematurely
When the tryptophan level in the cell is ______, the ribosome pauses in region 1 of the trp mRNA leader, causing region 2 to bind to region 3 and transcription to continue.
low
A mutation that changes the nucleotide sequence of the _____________, so that the repressor is no longer able to bind to the site, will cause a constitutive synthesis of the lactose-utilizing proteins.
operator
The lac operon structural genes are transcribed as _____.
part of a single polycistronic mRNA with three independent ribosome binding sites
Allolactose is a small effector molecule that binds to the Lac repressor and ______.
prevents repressor from binding to DNA
In the lac operon, some of the nucleotides of the operator are also part of the ______.
promoter
An element that acts in trans is typically a ______.
protein that can diffuse through the cytoplasm and act on any DNA target in the cell
Mutations in trans-acting elements typically occur in ______, while mutations in cis-acting elements occur in ______.
protein-encoding genes; protein-binding sites
Consider a bacterial cell with the genotype: lacI— lacZ+ lacY—/F' (lacI+ lacZ— lacY+). The expression of the genes lacZ+ and lacY+ is _____.
repressible in the absence of lactose and inducible in its presence
Consider a bacterial cell with the genotype lacI+ o+ lacZ+ lacY— that was transformed with an F' plasmid carrying lacIs o+ lacZ— lacY+. The expression of the genes lacZ+ and lacY+ in the merodiploid bacterium is ______.
repressible in the absence or presence of lactose
______ are allosteric RNA leaders that bind small effector molecules to control gene expression.
riboswitches
The conversion of a riboswitch from one conformation to another is due to _____.
the binding of a small molecule
When lactose is depleted from the environment, ______.
the repressor reverts to its DNA-binding shape
What do riboswitches regulate?
transcription and translation
Riboswitches can regulate ______.
transcription or translation
Small RNA (sRNA) molecules regulate _____.
translation in trans by base-pairing with mRNAs
Select the genes in the trp operon.
trpB trpC trpE trpA trpD
The ribosome-binding site is a special initiation site located ______.
upstream (near the 5' end) of the open reading frame
The small effector molecule ________prevents the Lac repressor from binding to the operator site.
Allolactose/inducer
RNA leader sequences are __________in that they can alter their stem-loop structures and thus their function in response to a wide variety of environmental cues.
Allosteric
Regulatory RNAs that are transcribed from the opposite DNA strand to that of the mRNA are called ___________RNAs.
Antisense
Pathways that break down complex molecules into smaller units are termed_______^ , while pathways that construct end product molecules from simpler units are called _______
Catabolic; anabolic
Antisense RNA is an RNA strand that is ___________to an mRNA molecule.
Complementary
The small nucleotide ___________ (cAMP) binds to a protein called CRP, and the complex can positively regulate the lac operon.
Cyclic adenosine monophosphate
The helix-turn-helix motif is commonly found in _____.
DNA-binding proteins
Which of the following techniques is used to study protein-DNA interactions?
DNAseI footprinting
The lacI+ allele is ______ to lacI— in ______.
Dominant; trans
An inducer is a small effector molecule that causes transcription to ______.
increase
Constitutive mutants ______.
synthesize certain proteins all the time
A molecule that can stimulate production of a protein is called a(n)
Inducer
In the absence of lactose, the Lac ____________binds to the operator, and this binding blocks transcription of the lac operon
Repressor
A constitutive mutant of the lac operon will _____.
synthesize Lac permease even in the absence of lactose
The base sequences of all the RNAs that a cell produces under a particular set of conditions is known as the
Transcriptome
The term sRNAs refers to _________RNA molecules that regulate translation by base-pairing with mRNAs in bacteria.
Small
RNA leader sequences can form secondary structures called _______. These can terminate transcription of the rest of the mRNA prematurely.
Stem loops