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LESSON - 37
GENE REGULATION
TRANSCRIPTIONAL CONTROL IN PROKARYOTES.
A.
Objectives.
Describe the general structure of an operon; define promotor, operator, regulator,
repressor, activator, structural gene;
Explain how substrate availability regulates transcription of genes of catabolic
enzymes and product accumulation regulates transcription of genes of anabolic
enzymes
Diferentiate between positive and negative regulation and between regulation by
induction and repression of transcription; Explain 4 different types of regulation of
transcription; Explain the two control mechanisms of the Lac operon.
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B.
Lecture Outline.
Read:
1.
ORGANIZATION OF AN OPERON.
a.
b.
c.
2.
the promotor binds RNA polymerase.
the operator binds the regulator: repressor or activator/inducer
the transcription unit is transcribed:
EXAMPLES OF GENE EXPRESSION.
a.
b.
3.
Gene regulation in bacteria (SBM p306-312)
The lactose breakdown: substrate induces transcription of the genes of catabolic
enzymes. [Figure 14-2 (SBM p307)]
The tryptophan synthesis: product represses transcription of genes of anabolic
enzymes. [Figure 14-4 (SBM p310)]
GENERALIZATION.
a.
b.
c.
positive and negative control.
induction and repression.
4 different types of regulation of transcription.
negative control with induction of transcription.
negative control with repression of transcription.
positive control with induction of transcription.
negative control with repression of enzyme control.
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—
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—
4.
COMBINATION OF SWITCHES: THE Lac OPERON.
Read: Figure 14-5 (SBM p311)
C.
Study Questions.
LESSON - 38
GENE REGULAUTION
EUKARYOTES
A. Objectives.
Explain how eukaryotic gene expression is regulated at multiple levels; describe the
structure of the eukaryotic operon, define its elements; explain how different
transcription factors cooperate to regulate gene expression.
Explain how proteins can bind to specific DNA sequences; define the major and minor
groove of DNA; define helix—turn-helix, homeodomain, zinc finger and leucine
zipper domains;
Explain how gene function is controlled by RNA splicing, regulation of translation,
degradation of proteins, and regulation of enzyme activity.
—
B.
Lecture Outline.
1.
MULTIPLE LEVELS REGULATION OF EUKARYOTIC GENE EXPRESSION.
READ: Gene regulation in eukaryotic cells (SBM p312-319)
2.
TRANSCRIPTIONAL CONTROL OF THE EUKARYOTIC GENE
a.
b.
c.
d.
Core promotor: TATAAA—box.
basal transcription factors allow PNA polymerase to bind to the core promotor.
proximal control elements bind regulatory transcription factors.
distal control elements:
activators bind to enhancers.
repressors bind to silencers.
coactivators link enhancers to basal or regulatory
transcription factors.
—
—
—
3.
HOW TRANSCRIPTION FACTORS BIND SPECIFIC DNA SEQUENCES
a.
b.
c.
d.
4.
the helix-turn-helix motif.
the homeodomain motif.
the zinc finger motif.
the leucine zipper motif.
POST-TRANSCRIPTIONAL CONTROL IN EUKARYOTES.
a.
b.
c.
d.
e.
RNA processing and RNA splicing.
translational control: selecting which mRNAS are translated.
posttranslational control: e.g., glycosylation, targeting
ubiquitin-dependeflt protein degradation
regulation of enzyme activity.
C. Study Questions.
1.
Control of gene expression allows bacterial cells to
A.
be more beautiful.
B.
participate in regulating the multicellular body.
C.
take advantage of a changing environment.
D. separate catabolic and anabolic reactions.
E.
separate replication, transcription, and translation.
2.
The primary function of gene regulation in multicellular organisms is
A.
be more beautiful.
B.
participate in regulating the multicellular body.
C.
take advantage of a changing environment.
D. separate catabolic and anabolic reactions.
E.
separate replication, transcription, and translation.
3.
In multicellular organisms, regulation of gene expression is critical for directing
A.
cell size.
B.
uptake of nutrients.
C.
catabolism.
D. development.
E.
DNA replication.
4.
The most common form of regulation of gene function in both prokaryotes and eukaryotes is
A.
translational control.
B.
posttranslationaJ. control.
C.
ubiquitin-dependent protein degradation.
D. regulation of enzyme activity. E. transcriptional control.
5.
Proteins that regulate transcription bind to
A.
base pairs exposed in the major groove of DNA.
B.
base pairs exposed in the minor groove of DNA.
C.
repeating ribosyl residues in the backbone of DNA.
D. DNA polymerase.
E.
ribosomes.
Eukaryotic transcription factors bind to
A.
base pairs exposed in the major groove of DNA.
B.
base pairs exposed in the minor groove of DNA.
C.
repeating ribosy]. residues in the backbone of DNA.
D. DNA polymerase.
E.
ribosomes.
6.
7.
A common structural motif of a transcription factor is
A.
a alpha-helix.
B.
anti—parallel helices.
C.
beta-pleated sheets.
D. zinc finger.
E.
branching polymers.
7.
A common structural motif of a transcription factor is
A.
a alpha-helix.
B.
anti—parallel helices.
C.
beta—pleated sheets.
D. helix—turn—helix.
E.
branching polymers.
8.
A common structural motif of a transcription factor is
A.
a alpha—helix.
B.
anti—parallel helices.
C.
beta—pleated sheets.
D. leucine zipper.
E.
branching polymers.
8.
particular bends of a protein chain that permits it to interlock with the major groove of the DNA helix is
called a
A.
active center.
B.
structural motif.
C.
enhancer site.
D. operator..
E.
promotor.
9.
A structural motif of a transcription factor that consists of two alpha- helical segments linked with a short
nonhelical segment at right angles from each other is called a
A.
beta-pleated sheet motif.
B.
helix—turn-helix motif.
C.
zinc finger motif.
D.
leuzine zipper motif.
E.
homeodomain motif.
10.
A structural motif of a transcription factor that consists of a zinc atom that links an alpha —helical segment to
a beta-pleated sheet segment in such a way that the helical segment fits in the major groove of DNA is called
a
A.
beta—pleated sheet motif.
B.
helix—turn—helix motif.
C.
zinc finger motif.
D.
leuzine zipper motif.
E.
homeodomain motif.
11.
A structural motif of a transcription factor that consists of Y-shaped structure in which an alpha-helix with
regularly arranged leucine residues in one subunit interacts with a similar region in a second polypeptide
called a
A.
beta—pleated sheet motif.
B.
helix—turn-helix motif.
C.
zinc finger motif.
D.
leuzine zipper motif.
E.
homeodomain motif.
12.
The strength with which a zinc finger transcription factor binds to DNA is determined by the number of
A.
number of zinc atoms.
B.
length of the alpha-helix.
C.
length of the beta-sheet.
D.
number of zinc fingers.
E.
leucine residues.
13.
The promotor of a gene/operon is the site of binding of the
A.
ribosomes.
B.
operator.
C.
RNA polymerase.
D.
DNA polymerase.
E.
proteasome.
14.
The operator of a bacterial operon binds the
A.
regulator.
B.
C.
D.
E.
RNA polymerase.
DNA polymerase.
aminoacyl tRNA.
3’ poly(A) tail.
15.
Bacteria use activators and repressors to regulate gene expression
A.
replicationally.
B.
translationally.
C.
transcriptionally.
D.
post—translationally.
E.
enzymatically.
16.
In contrast to the mRNA of prokaryotes, mRNA of multicellular organisms is much
A.
thicker.
B.
longer.
C.
labile.
D.
more stable.
E.
double-stranded.
17.
mRNA of bacteria is unstable because bacteria
A.
have a high metabolism.
B.
need to respond quickly to a changing environment.
C.
live in a rather stable environment.
D.
have nucleic acids that are inherently very labile.
E.
have many different nucleases.
18.
mRNA of cells of multicellular organisms is very stable because
A.
B.
C.
D.
E.
the cells reside in a very stable, predictable tissue/body environment.
most cells of multicellular eukaryotes are committed to the synthesis of a relatively small collection
of gene products.
the cells need to respond quickly to a changing environment.
Both A and B are correct.
Both A, B, and C are correct.
19.
Unlike the normal stable mRNAs, the mRNA of regulatory proteins and growth factors of multicellular
organisms are unstable because they are the targets of
A.
DNAses.
B.
RNAses.
C.
proteinases.
D. ribosomea.
E.
transcription factors.
20.
Which of the following is the hallmark of multicellular organisms?
A.
grow and divide rapidly.
B.
cells adjust quickly to outside environments.
C.
homeostasis.
D. quickly synthesize enzymes according to available nutrients.
E.
respond by gene action to oxygen availability.
21.
Prokaryotes and eukaryotes both use the following ways to control gene expression except
A.
RNA processing control.
B.
translational control.
C.
protein phosphorylation control.
D. transcriptional control.
E.
mRNA degradation control.
22.
The basic tool of gene regulation is the ability of certain proteins to bind to specific
A.
B.
C.
D.
E.
regulatory RNA sequences.
regulatory DNA sequences.
repressor parts of the gene.
promotor part of the gene.
enzymes of the cell.
23.
Which oif the following is NOT true about control of gene expression?
A.
It allows bacteria to adapt to changing environments.
B.
It is a critical aspect of development of multicellular organisms.
C.
It allows bacteria to replicate without control.
D. It allows multicellular organisms to maintain homeostasis.
E.
It allows multicellular organisms to divide different tasks among different cells.
24.
For controlling transcription,
A.
DNA polymerase must have access to the DNA double helix.
B.
RNA must be capable to bind to the gene’s promotor.
C.
proteins binding at other regions on DNA affect the binding of .RNA polymerase to its promotor.
D. only B and C are required.
E.
A, B, and C are required.
25.
RNA polymerase binds to a site on DNA called the
A.
operator.
B.
repressor.
C.
footprint.
D. promotor.
E.
operon.
26.
Transcriptional controls are exerted by means of
A.
DNA sequences that are translated.
B.
short DNA sequences that are not translated.
C.
specific amino acids.
D. RNA sequences that are not spliced.
E.
RNA sequences that are spliced.
27.
Proteins that bind to regulatory sequences have shapes that fit into the
A.
major groove of ribosomes.
B.
minor groove of RNA.
C.
major groove of RNA.
D. minor groove of DNA.
E.
major groove of DNA.
28.
All of the following are structural motifs employed by the regulatory proteins except the
A.
zinc finger.
B.
helix—turn—helix.
C.
homeodomain.
D. TATAAP1 box.
E.
leucine finger.
29.
In gene regulation, negatiove control is exerted by a(n)
A.
activator.
B.
operon.
C.
repressor.
D.
regulator.
E.
promotor.
30.
In gene regulation, a gene is “turned on” by a(n)
A.
activator.
B.
C.
D.
E.
operon.
repressor.
regulator.
promotor.
31.
A bacterial gene regulatory system is likely to have all of the following except
A.
a coding sequence.
B.
an operator.
C.
a promotor.
D.
a regulator.
E.
one or more introns.
32.
The lac regulatory system of bacteria consists of three structural genes plus a regulatory sequence; taken
together this complex makes up
A.
an encoded gene.
B.
an operator.
C.
an operon.
D.
a regulator.
E.
a translational unit.
33.
Synthesis of catabolic enzymes in bacteria is usually
A.
induced by their product.
B.
induced by their substrate.
C.
repressed by their product.
D.
repressed by their substrate.
34.
Synthesis of anabolic enzymes in bacteria is usually
A.
induced by their product.
B.
induced by their substrate.
C.
repressed by their product.
D.
repressed by their substrate.
35. If genes are transcribed when the regulator is bound to the operator, there is
A.
positive control.
B.
negative control.
C.
induction control.
D.
activation control.
E.
repression control.
36.
If genes are transcribed when the regulator is released from the operator, there is
A.
positive control.
B.
negative control.
C.
induction control.
D.
activation control.
E.
repression control.
37.
When fucose is present in the environment, the sugar binds to its repressor. The complexed regulator binds to
its operator and allows transcription of the genes coding for enzymes that digest fucose. There is
A.
negative control with induction of enzyme synthesis.
B.
negative control with repression of enzyme control.
C.
positive control with induction of enzyme synthesis.
D.
positive control with repression of enzyme synthesis.
38.
Only the free regulator of the tyrosine operon can bind to the tyrosine operator and as such stimulate
transcription of the tyrosine genes. When complexed with tyrosine, the regulator looses its ability to bind to
the operator. There is
A.
B.
C.
D.
negative control with induction of enzyme synthesis.
negative control with repression of enzyme control.
positive control with induction of enzyme synthesis.
positive control with repression of enzyme synthesis.
39.
Only when the proline regulator is complexed with proline can the complex bind to the proline regulator.
Transcription of the proline genes is prevented by the presence of the regulator on the proline operator. There
is
A.
negative control with induction of enzyme synthesis.
B.
negative control with of enzyme control.
C.
positive control with of enzyme synthesis.
D.
positive control with of enzyme synthesis.
40.
Transcription of sucrose-digesting genes is prevented by the presence of the sucrose regulator on its operator.
The regulator is released from the operator when it binds sucrose. There is
A.
negative control with induction of enzyme synthesis.
B.
negative control with repression of enzyme synthesis.
C.
positive control with induction of enzyme synthesis.
D.
positive control with repression of enzyme synthesis.
41.
The iac operon of E. coil has two control mechansisms. Positive control is exerted by the binding to DNA of
A.
cAMP.
B.
lactose.
C.
Catabolite Activator (Repressor) Protein.
D.
lactose repressor.
E.
phosphate.
42.
The iac operon of E. coil has two control mechanisms. Negative control is exerted by the binding to DNA of
A.
cAMP.
B.
lactose.
C.
Catabolite Activator (Repressor) Protein.
D.
lactose repressor.
E.
phosphate.
43. The Lac operon of E. coli has two control mechanisms. Binding of RNA polymerase to the promotor is
prevented by the presence of
A.
cAMP.
B.
lactose.
C.
Catabolite Activator (Repressor) Protein.
D.
lactose repressor.
E.
phosphate.
44.
The iac operon of E. coii has two control mechansisms. Binding of the RNA polymerase to its promotor
requires the presence of
A.
cAMP.
B.
lactose.
C.
Catabolite Activator (Repressor) Protein.
D.
lactose repressor.
E.
phosphate.
45.
The binding of lactose
A.
activates the iac operon repressor.
B.
inactivates the lac operon repressor.
C.
activates Catabolic Activator (Repressor) Protein.
D.
inactivates Catabolic Activator (repressor) Protein.
E.
activates RNA polymerase.
46.
The binding of cAMP
A.
activates the iac operon repressor.
B.
inactivates the iac operon repressor.
C.
activates Catabolic Activator (Repressor) Protein.
D.
inactivates Catabolic Activator (repressor) Protein.
E.
activates RNA polymerase.
47.
RNA polymerase can bind only to the iac operon promotor only in the presence on DNA of
A.
B.
C.
D.
E.
48.
49.
the lactose repressor.
the Catabolite Activator (Repressor) Protein.
lactose.
cAMP.
both A and B.
Lactose is an _______ of the lac operon; cAMP is an _______ of the lac operon.
A.
inducer, repressor.
B.
repressor, inducer.
C.
inducer, inducer.
D.
repressor, repressor.
E.
coactivators.
Which of the following are NOT transcription factors of eukaryotic cells?
A. basal transcription factors.
B.
regulatory transcription factors.
C.
activators.
D.
repressors.
E.
coactivators.
50.
Which of the following transcription factors bind RNA polymerase to the promotor?
A.
basal transcription factors.
B.
regulatory transcription factors.
C.
activators.
D. repressors.
E.
coactivators.
51.
Transcription factors bind to A. mRNA.
B.
ribosomes.
C.
DNA sequences.
D. amino acid sequences.
E.
oligosaccharide moieties.
52.
Which of the following transcription factors binds to the proximal control elements?
A.
basal transcription factors.
B.
regulatory transcription factors.
C.
activators.
D. repressors.
E.
coactivators.
53.
Which of the following transcription factors binds to silencers?
A.
basal transcription factors.
B.
regulatory transcription factors.
C.
activators.
D. repressors.
E.
coactivatora.
54.
Which of the following transcription factors binds to enhancers?
A.
basal transcription factors.
B.
regulatory transcription factors.
C.
D.
E.
activators.
repressors.
coactivators.
55.
Basal transcription factors bind to
A.
silencers.
B.
enhancers.
C.
proximal control elements.
D.
core promoter.
E.
Catabolite Activator Protein.
56.
Regulatory transcription factors bind to
A.
silencers.
B.
enhancers.
C.
proximal control elements.
D. core promotor.
E.
Catabolite Activator Protein.
57.
Activators bind to
A.
silencers.
B.
enhancers.
C.
proximal control elements.
D. core promotor.
E.
Catabolite Activator Protein.
58.
Repressors bind to
A.
silencers.
B.
enhancers.
C.
proximal control elements.
D. core promotor.
E.
Catabolite Activator Protein.
59.
Which of the following transcription factors binds to the core promotor?
A.
basal transcription factors.
B.
regulatory transcription factors.
C.
activators.
D. repressors.
60.
Distal control elements include A. silencers.
B.
enhancers.
C.
basal transcription factors.
D.
regulatory transcription factors.
E.
Catabolite Activator Protein.
61.
Eukaryotic activators bind to
A.
coactivators or other transcription factors.
B.
DNA sequences.
C.
RNA sequences.
D.
both A and B.
E.
both A, B, and C.
62.
A DNA sequence of regulatory function to which repressors or inducers bind is the
A.
operon.
B.
repressor.
C.
promoter.
D.
operator.
E.
Catabolite Activator (Repressor) Protein.
63.
Post-transcriptional control in eukaryotic cells includes all of the following except
A.
processing of the primary RNA transcript.
B.
translational control.
C.
ubiquitin-dependent proteolysis.
D.
selective diestion of mRNA
E.
digesting the DNA sequence immediately after translation.
64.
A protein that regulates transcription by binding to the operator is the
A.
operon.
B.
repressor.
C.
promotor.
D.
operator.
E.
Catabolite Activator (Repressor) Protein.
65.
A protein that initiates the transcription of genes of the lac operon at low glucose concentrations is the
A. operon.
B. repressor.
C. promotor.
D. operator.
E. Catabolite Activator (Repressor) Protein.
66.
A site at the 5’ end of a gene to which RNA polymerase attaches to initiate transcription is the
A.
operon.
B.
repressor.
C.
promotor.
D.
operator.
E.
Catabolite Activator (Repressor) Protein.
67.
A cluster of functionally-related genes and their regulatory DNA sequences is an
A.
operon.
B.
repressor.
C.
promotor.
D.
operator.
E.
Catabolite Activator (Repressor) Protein.
68. Genes that encode proteins that are always needed are called:
A.
B.
C.
D.
E.
repressible genes.
promoter genes.
constitutive genes.
inducible genes.
operons.
69. The researchers who first discovered the mechanism of control of a bacterial gene were:
A.
B.
C.
D.
E.
Hershey and Chase.
Griffith and Avery.
Watson and Crick.
Jacob and Monod.
McClintock and Morgan.
70. The operator of the lactose operon in E. coli is located:
A.
B.
C.
D.
E.
between the promoter and the TATA box.
upstream of the promoter.
between the promoter and the structural genes.
among the structural genes.
anywhere on the chromosome.
71. How does the lactose repressor block transcription of the lactose operon?
A.
B.
C.
D.
E.
by “turning off” the appropriate genes in the intron
by regulating the activity of the enzymes that the operon codes for
by binding allosterically to the appropriate genes
by slowing the uptake of lactose into the cell
by binding to the operator
72. The gene that codes for the repressor protein of the E. coli lactose operon is:
A.
B.
C.
D.
E.
located between the operator and the promoter.
downstream from the promoter region.
downstream from the operator.
constitutive.
turned off most of the time.
73. The molecular switch that controls gene expression is known as:
A.
B.
C.
D.
E.
the operon.
controller.
the operator.
repressor.
inducer.
74. Lactose induces the transcription of the lactose operon by:
A.
B.
C.
D.
E.
binding to the allosteric site of the repressor after being converted to allolactose.
stimulating lactose metabolism in the cell.
binding to the glucose operon, making it inoperable.
binding to the allosteric site of RNA polymerase.
inhibiting the activity of CAP.
75. The inducer of the lactose operon in E. coli is:
A.
B.
C.
D.
E.
CAP.
AMP.
allolactose.
glucose.
galactose.
76. Inducible genes are usually actively transcribed when:
A.
B.
C.
D.
E.
the molecule degraded by the enzyme(s) is present in the cell.
repressor molecules bind to the promoter.
lactose is absent from the cell.
quantities of precursor materials are low.
there is no other substrate that can be used by the cell.
77. Repressible genes are usually actively transcribed when:
A.
B.
C.
D.
E.
repressor molecules bind to the promoter.
the supply of the end product formed by the enzymes encoded by these genes is low.
tryptophan accumulates in the cell.
quantities of precursor materials are high.
there is no other substrate that can be used by the cell.
78. An inducible operon is usually controlled by:
A.
B.
C.
D.
E.
an inducer molecule that keeps it in the “off” state.
an active repressor that keeps it in the “off” state.
being active at all times.
allolactose.
being turned “off,” usually by the end product of the pathway.
79. Bacterial enzymes that are part of a rarely used catabolic pathway are usually organized into a(n)
________________.
A.
B.
C.
D.
E.
inducible operon
repressible operon
inducible zinc finger
repressible leucine zipper
inducible catabolon
80. A repressible operon is usually controlled by:
A.
B.
C.
D.
E.
an inactive repressor that allows it to be in the “on” state.
the supply of the precursor product for the enzymes.
an inactive repressor that keeps it in the “off” state.
tryptophan.
being turned “on,” usually by the end product of the pathway.
81. In the tryptophan operon, the repressor actively binds to the operator when:
A.
B.
C.
D.
E.
tryptophan binds to an allosteric site on the repressor.
tryptophan levels are low.
lactose levels are low.
there is a great need for proteins.
allotryptophan levels are low.
82. An activator protein would have which of the following effects on an operon with a positive control
mechanism?
A.
B.
C.
D.
E.
stimulate transcription
turn off transcription
stimulate transcription when a coactivator is bound to the allosteric site
inhibit transcription when a coactivator is bound to the allosteric site
no response
83. Catabolite activator protein:
A.
B.
C.
D.
E.
increases the affinity of the promoter region for RNA polymerase.
decreases RNA polymerase activity.
becomes nonfunctional when it binds to AMP.
binds and activates RNA polymerase.
blocks RNA polymerase access to the DNA template.
84. cAMP levels decrease when ______________________________. This results in ____________ of CAP.
A.
B.
C.
D.
E.
lactose levels increase; activation
lactose levels decrease; inhibition
glucose levels increase; inhibition
glucose levels decrease; activation
glucose levels decrease; inhibition
85. In the lac operon, cAMP binds to:
A.
B.
C.
D.
E.
DNA.
the repressor gene.
the operator gene.
the repressor protein.
catabolite activator protein.
86. The role of CAP in the lac operon is:
A.
B.
C.
D.
E.
repression of RNA polymerase binding to the promoter.
negative control of the lac operon.
enhancement of RNA polymerase binding to the promoter.
to inactivate the repressor by binding to its allosteric site.
the activation of allolactose binding to the repressor protein.
87. Translational controls regulate:
A.
B.
C.
D.
E.
the activity of a protein end-product that is produced.
the rate at which an mRNA molecule is translated.
the rate at which an mRNA molecule is synthesized.
the uptake of nucleic acids into the cell.
the attachment of phosphate groups to polypeptides.
88. A repressor protein would have which of the following effects on repressible genes with a negative control
mechanism?
A.
B.
C.
D.
E.
stimulate transcription in the presence of a corepressor
turn off transcription in the presence of an inducer
stimulate transcription in the presence of a coactivator
turn off transcription in the presence of a corepressor
no response
89. A new operon is discovered in a bacterium. The control of this operon is affected by a protein that is made by
another gene, and is made in an active form that binds to the DNA near the operon to prevent transcription. This
is an example of ________________ control.
A.
B.
C.
D.
E.
positive
negative
activational
repressing
inducing
90. Bacterial gene regulation occurs mainly at the _________________ level.
A.
B.
C.
D.
E.
translational
transcriptional
posttranscriptional
feedback inhibition
posttranslational
91. Which of the following statements about the regulation of gene expression in bacteria is false?
A.
B.
C.
D.
E.
Genes can be turned on and off as environmental conditions change.
Constitutive genes producing enzymes that are more stable are transcribed at a slower rate.
Most gene regulation in bacteria occurs at the level of translation.
Constitutive genes encoding proteins required in large amounts are transcribed more rapidly than
genes for proteins required in smaller amounts.
Constitutive genes with “strong” promoters bind RNA polymerase more frequently than genes with
“weak” promoters.
92. Translational controls of protein levels in bacteria are governed by:
A.
B.
C.
D.
E.
93-95.
the rate at which small and large subunits of ribosomes assemble.
the rate at which the cap and tail of pre mRNA are removed.
the rate at which ribosomes attach to mRNA molecules.
the concentration of proteins in the cytoplasm.
the rate at which sugars are incorporated into the cell.
Use the figure to answer the corresponding questions.
93. The area of the tryptophan operon labeled 3 is the:
A.
B.
C.
D.
E.
promoter.
repressor gene.
ribosome.
RNA polymerase.
None of these.
94. The structure labeled 7 in the figure of the tryptophan operon is:
A.
B.
C.
D.
E.
an active repressor protein.
an inactive repressor protein.
an active RNA polymerase.
an inactive RNA polymerase.
A ribosome.
95. The promoter in the figure is labeled ____________.
A.
B.
C.
D.
E.
6
3
1
2
7
96. The scenario in the accompanying figure reflects conditions of:
A.
B.
C.
D.
E.
low levels of lactose.
high levels of lactose.
low levels of glucose.
high levels of glucose.
None of these.
97. Feedback inhibition is:
A.
B.
C.
D.
E.
transcriptional control.
transcriptional control.
a mechanism affecting events after translation.
a repressible system.
None of these.
98. Feedback inhibition of the first enzyme of a pathway by the end product of the pathway is an example of:
A.
B.
C.
D.
E.
translational control.
posttranslational control.
transcriptional control.
inhibiting control.
repression.
99. Which of the following statements concerning gene regulation in eukaryotes is FALSE?
A.
B.
C.
D.
E.
The organization of tissues and organs is regulated mainly via transcription.
Some eukaryotic genes are constitutive.
Eukaryotic genes do not usually form operon-like clusters.
“Housekeeping” enzymes are expressed at all times.
Eukaryotic cells lack inducible genes.
100. Temporal gene regulation refers to which of the following circumstances?
A.
B.
C.
D.
E.
Certain genes are induced only at a particular point in the life cycle.
Certain genes are induced only in specific tissues.
Heat-shock genes are induced during periods of temperature stress.
“Housekeeping” genes are induced in response to a viral infection.
Molecular chaperones are synthesized after heavy-metal ingestion.
101. Densely staining regions of highly compacted chromatin that are generally not transcribed are:
A.
B.
C.
D.
E.
heterochromatin.
homochromatin.
histone-dependent chromatin.
primary chromatin.
None of these.
102. Genes in euchromatic regions are:
A.
B.
C.
D.
E.
inhibited.
duplicated
actively being transcribed.
repressed.
unregulated.
103. In female mammals, most of the inactive X chromosome has become:
A.
B.
C.
D.
E.
associated with histones.
active X factor.
euchromatin.
replicated.
heterochromatin.
104. DNA sequences that are methylated by a cell are usually genes that:
A.
B.
C.
D.
E.
have been replicated
are actively expressed.
are inactive.
are constitutive.
are repressed.
105. The rate of eukaryotic transcription after initiation is affected by:
A.
B.
C.
D.
E.
upstream promoter elements.
groups of genes arranged into operons.
the action of catabolite activator proteins.
how fast caps and tails can be added to pre-mRNA.
enhancers.
106. A TATA box is seen in ______________ cells and is the site where _______________________.
A.
B.
C.
D.
E.
bacterial; RNA polymerase binds
eukaryotic; DNA ligase cleaves introns
eukaryotic; RNA polymerase binds
both bacterial and eukaryotic; transcription factors bind
bacterial; a repressor protein binds
107. Upstream promoter elements in eukaryotes are:
A.
B.
C.
D.
E.
nucleotide sequences that act as binding sites for RNA polymerase.
nucleotide sequences that regulate the efficiency of transcription initiation.
nucleotide sequences that contain the TATA box.
proteins that enhance RNA polymerase binding to the promoter.
proteins that inhibit RNA polymerase binding to the promoter.
108. Eukaryotic enhancers are capable of which of the following?
A.
B.
C.
D.
E.
regulating a gene even if they are cut out of the DNA and reinserted inverted
regulating a gene from very long distances
interacting with proteins that regulate transcription
increasing the rate of RNA synthesis after initiation
All of these
109. DNA sequences called ____________ increase the rate of RNA synthesis after initiation of transcription.
A.
B.
C.
D.
E.
promoters
TATA boxes
UPEs
enhancers
regulators
110. Eukaryotic transcription factors:
A.
B.
C.
D.
E.
are always simpler than bacterial regulators.
may be activators or repressors of transcription.
are inducers.
are corepressors.
are also known as enhancers.
111. Gene amplification involves:
A.
B.
C.
D.
E.
increasing the affinity of a gene to DNA polymerase.
extra replication of genes that specify a certain gene product only in cells needing this product.
improving the accuracy by which a gene is copied to produce an mRNA molecule.
enhancing the activity of RNA polymerase.
increasing the size of the gene that encodes a needed protein.
112. A cell may meet the need for large quantities of a specific protein by:
A.
B.
C.
D.
E.
continuously synthesizing the mRNA molecule that specifies that protein.
increasing the half-life of the mRNA that specifies the protein.
having multiple copies of the gene that codes for that protein.
All of these.
None of these.
113. Which of the following statements concerning leucine zipper proteins is FALSE?
A.
B.
C.
D.
E.
114-115.
They are transcription factors.
They contain loops held together by zinc ions.
They form homodimers.
They form heterodimers.
They contain DNA-binding domains.
Use the figure to answer the corresponding questions.
114. The type of expression illustrated in the
accompanying figure is:
A.
B.
C.
D.
E.
a typical bacterial gene.
a weakly expressed bacterial gene.
a strongly expressed eukaryotic gene.
a weakly expressed eukaryotic gene.
a gene stimulated by an enhancer.
115. The structure labeled 2 in the associated figure is:
A.
B.
C.
D.
E.
the enhancer.
the TATA box.
the Pribnow box.
the transcription initiation site.
the transcription termination site.
116. Which of the following types of processing does eukaryotic mRNA undergo before it becomes functional?
A.
B.
C.
D.
E.
splicing
capping
polyadenylation
removal of introns
All of these.
117. Proteolytic processing of eukaryotic proteins involves:
A.
B.
C.
D.
E.
removal of a portion of the polypeptide chain from an inactive precursor of the protein.
the addition of one or more functional groups to a precursor protein.
the removal of one or more functional groups from a precursor protein.
removal of histones.
removing the cap and tail of a newly synthesized protein.
118. Some eukaryotic DNA sequences act as introns in the cells of some tissues and exons in the cells of other
tissues. This allows:
A.
B.
C.
D.
E.
prevention of harmful mutation.
regulation of the rate of transcription.
formation of different types of closely related proteins.
regulation of the rate of translation.
repression of DNA replication.
119. In eukaryotes, some DNA sequences act as introns in some cells and as exons in other cells. This is an
example of ______________________.
A.
B.
C.
D.
E.
gene repression
mRNA splicing
gene amplification
differential mRNA processing
gene processing
120. Increasing the stability of a particular mRNA _________________ the expression of that gene.
A.
B.
C.
D.
E.
increases
does not affect
eliminates
decreases
None of these.
121. Enzymes that alter another protein or enzyme’s activity by attaching a phosphate group are called:
A.
B.
C.
D.
E.
kinases.
phosphatases.
phospators.
transcription factors.
coenzymes.
122. The regulation of most bacterial genes occurs at the level of
A.
B.
C.
D.
E.
transcription
translation
replication
posttranslation
postreplication
123. The operator of an operon
A.
B.
C.
D.
E.
encodes information for the repressor protein
is the binding site for the inducter
is the binding site for the repressor protein
is the binding site for RNA polymerase
encodes the information for the CAP
124. A mutation that inactivates the repressor gene of the lac operon results in
A.
B.
C.
D.
E.
the continuous transcription of the structural genes
no transcription of the structural genes
the binding of the repressor to the operator
no production of RNA polymerase
no difference in the rate of transcription
125. At a time when the lac operon is actively transcribed,
A.
B.
C.
D.
E.
the operator is bound to the inducer
the lactose repressor protein is bound to the promoter
the operator is not bound to the promoter
the gene coding for the repressor is not expressed constitutively
the lactose repressor protein is bound to the inducer
126. An mRNA molecule transcribed from the lac operon contains nucleotide sequences complementary to
A.
B.
C.
D.
E.
structural genes coding for enzymes
the operator region
the promoter region
the repressor gene
introns
127. Feedback inhibition is an example of control at the level of ________________-.
A.
B.
C.
D.
D.
transcription
translation
posttranslation
replication
all the preceding
128. Which of the following control mechanisms is generally the most economical in terms of conserving energy
and resources?
A.
B.
C.
D.
E.
control by means of operons
feedback inhibition
selective degradation of mRNA
selective degradation of enzymes
gene amplification
129. A repressible operon, such as the trp operon, is “off” when
A.
B.
C.
D.
E.
the gene that codes for the repressor is expressed constitutively
the repressor-corepressor complex binds to the operator
the repressor binds to the structural genes
the corepressor binds to RNA polymerase
CAP binds to the promoter
130. Which of the following is an example of positive control?
A.
B.
C.
D.
E.
transcription occurs when a repressor binds to an inducer
transcription cannot occur when a repressor binds to a corepressor
transcription is stimulated when an activator protein binds to DNA
a and b
a and c
131. Which of the following are typically absent in bacteria?
A.
B.
C.
D.
E.
enhancers
proteins that regulate transcription
repressors
promoters
operators
132. The “zipper” of a leucine zipper protein attaches
A.
B.
C.
D.
E.
specific amino acids to specific DNA base pairs
two polypeptide chains to each other
one DNA region to another DNA region
amino acids to zinc atoms
RNA polymerase to the operator
133. Inactive genes tend to be found in
A.
B.
C.
D.
E.
highly condensed chromatin, known as euchromatin
decondensed chromatin, known as euchromatin
highly condensed chromatin, known as heterochromatin
decondensed chromatin, known as heterochromatin
chromatin is not organized as nucleosomes
134. Which of the following is characteristic of genes and gene regulation in bacteria, but not in eukaryotes?
A.
B.
C.
D.
E.
presence of enhancers
capping of mRNAs
many chromosomes per cell
binding of DNA to regulatory proteins
no requirement for exon splicing
135. Which of the following is characteristic of genes and gene regulation in both bacteria and eukaryotes?
A.
B.
C.
D.
E.
promoters
noncoding DNA within coding sequences
enhancers
operons
DNA located in a nucleus
136. Which of the following is characteristic of genes and gene regulation in eukaryotes, but not in bacteria?
A.
enhancers
B.
operons
C.
promoters
D.
a and b
E.
a, b, and c
137. Through differential mRNA processing, eukaryotes
A.
reinforce gene activation
B.
prevent transcription of heterochromatin
C.
produce related but different proteins in different tissues
D.
amplify genes to meet the requirement of high levels of a gene product
E.
bind transcription factors to enhancer to activate transcription