Question 1

Transcriptional control that acts by regulating the continuation of transcription is called:

Accepted Answer

A)  riboswitching. 
B)  antitermination. 
C)  negative control. 
D)  operator mutation. 
E)  attenuation. 
A)  riboswitching. 
B)  antitermination. 
C)  negative control. 
D)  operator mutation. 
E)  attenuation. E

Question 2

Which parts of the DNA region shown in the diagram encode proteins? (I = lac repressor gene; Z, Y, A = lac operon structural genes; P = lac promoter; O = lac operator)

Accepted Answer

A)  P 
B)  I, P, O 
C)  P, O, Z, Y, A 
D)  I, Z, Y, A 
E)  I, P, O, Z, Y, A 
A)  P 
B)  I, P, O 
C)  P, O, Z, Y, A 
D)  I, Z, Y, A 
E)  I, P, O, Z, Y, A D

Question 3

If there are mutations that inactivate lacP and lacI, which of the following statements is true? (I = lac repressor gene; Z, Y, A = lac operon structural genes; P = lac promoter; O = lac operator)

Accepted Answer

A)  These are mutations that are, respectively, cis- and trans-acting on lac operon expression. 
B)  These are mutations that are, respectively, trans- and cis-acting on lac operon expression. 
C)  These will affect the expression of I only. 
D)  These will affect the expression of only Z, Y, and A. 
E)  These mutations will have no effect. 
A)  These are mutations that are, respectively, cis- and trans-acting on lac operon expression. 
B)  These are mutations that are, respectively, trans- and cis-acting on lac operon expression. 
C)  These will affect the expression of I only. 
D)  These will affect the expression of only Z, Y, and A. 
E)  These mutations will have no effect. A

Question 4

Which of the following is NOT a common DNA-binding motif?

Accepted Answer

A)  the helix-loop-helix motif 
B)  the beta sheet-alpha helix motif 
C)  the zinc-finger motif 
D)  the homeodomain motif 
E)  the leucine-zipper motif 
A)  the helix-loop-helix motif 
B)  the beta sheet-alpha helix motif 
C)  the zinc-finger motif 
D)  the homeodomain motif 
E)  the leucine-zipper motif

Question 5

What would happen to the lac operon in the absence of allolactose?

Accepted Answer

A)  The structural genes within the lac operon will be constitutively transcribed. 
B)  The activator protein will be bound to the operator, which will turn on the structural gene behind it. 
C)  The repressor regulator protein binds to the operator and prevents the transcription of the structural gene. 
D)  The catabolite activator protein becomes inactivated and no transcription occurs. 
E)  The cAMP level rises in the absence of allolactose, which in turn inactivates the transcription. 
A)  The structural genes within the lac operon will be constitutively transcribed. 
B)  The activator protein will be bound to the operator, which will turn on the structural gene behind it. 
C)  The repressor regulator protein binds to the operator and prevents the transcription of the structural gene. 
D)  The catabolite activator protein becomes inactivated and no transcription occurs. 
E)  The cAMP level rises in the absence of allolactose, which in turn inactivates the transcription.

Question 6

The lysC gene in Bacillus subtilis encodes the first enzyme in the metabolic pathway that generates lysine from its precursor molecule. In the presence of high concentrations of lysine, lysC expression is reduced. Researchers have generated mutant bacteria that produce the LysC enzyme constitutively, even in the presence of lysine. A mutant identified in this manner had two nucleotide changes in the 5' UTR of the lysC gene itself. These nucleotide changes are thought to affect the function of a riboswitch regulating transcription of lysC. Describe two possible ways in which the mutations might affect the function of this riboswitch.

Accepted Answer

1. The mutations may disrupt the seconda

Question 7

Fill in the blanks in this table with "yes" or "no" for each condition of lac operon regulation. The strain is wild type with no partial diploidy. The first line is filled in for reference. $$\begin{array} { | l | c | c | c | c | c | } 
\hline \text { Condition } & \begin{array} { c } 
\text { Allolactose } \
\text { levels high? }
\end{array} & \begin{array} { c } 
\text { lac repressor } \
\text { bound to } \
\text { operator? }
\end{array} & \begin{array} { c } 
\text { cAMP } \
\text { levels } \
\text { high? }
\end{array} & \begin{array} { c } 
\text { CAP bound to } \
\text { CAP-binding } \
\text { site? }
\end{array} & \begin{array} { c } 
\text { Transcription } \
\text { at highest } \
\text { level? }
\end{array} \
\hline \begin{array} { l } 
\text { high glucose } \
\text { no lactose }
\end{array} & \text { no } & \text { yes } & \text { no } & \text { no } & \text { no } \
\hline \begin{array} { l } 
\text { no glucose } \
\text { high lactose }
\end{array} & & & & & \
\hline \begin{array} { l } 
\text { high glucose } \
\text { high lactose }
\end{array} & & & & & \
\hline \begin{array} { l } 
\text { no glucose } \
\text { no lactose }
\end{array} & & & & & \
\hline
\end{array}$$

Accepted Answer

To fill in the blanks for the lac operon

Question 8

A promoter that affects only genes that are on the same piece of DNA is referred to as a(n) _____-acting promoter.

Accepted Answer

A)  cis 
B)  trans 
C)  enhancer 
D)  positive 
E)  negative 
A)  cis 
B)  trans 
C)  enhancer 
D)  positive 
E)  negative

Question 9

RNA molecules that are complementary to particular sequences on mRNA are called:

Accepted Answer

A)  complementary RNA. 
B)  sense RNA. 
C)  antisense RNA. 
D)  riboswitches. 
E)  ribozymes. 
A)  complementary RNA. 
B)  sense RNA. 
C)  antisense RNA. 
D)  riboswitches. 
E)  ribozymes.

Question 10

It is possible for a repressor to negatively regulate the expression of an operon because:

Accepted Answer

A)  the repressor induces the expression of the inducer by binding to the promoter that comes before the inducer gene. 
B)  one of the structural genes expressed in the operon negatively regulates the repressor. 
C)  the repressor-binding site overlaps the promoter site of the operon, allowing it to physically block the binding of RNA polymerase. 
D)  the repressor-binding site on the DNA overlaps with the translation start site, thereby preventing the transcription. 
E)  the repressor physically blocks where the activator should be binding on the operator region. 
A)  the repressor induces the expression of the inducer by binding to the promoter that comes before the inducer gene. 
B)  one of the structural genes expressed in the operon negatively regulates the repressor. 
C)  the repressor-binding site overlaps the promoter site of the operon, allowing it to physically block the binding of RNA polymerase. 
D)  the repressor-binding site on the DNA overlaps with the translation start site, thereby preventing the transcription. 
E)  the repressor physically blocks where the activator should be binding on the operator region.

Question 11

A deletion occurs in the trp operon DNA of E. coli and results in the loss of the attenuation region in the 5'UTR of the RNA. The DNA sequences of the structural genes and the operator/promoter region are not affected by deletion. What effect will this deletion be expected to have on the regulation of this mutant trp operon compared to a wild-type operon?

Accepted Answer

A)  In the presence of tryptophan, transcription of the structural genes will be enhanced compared with a wild-type operon. 
B)  In the absence of tryptophan, transcription of the structural genes will be reduced compared with a wild-type operon. 
C)  In the presence of tryptophan, the repressor will bind to the operator/promoter region in the mutant operon more strongly than in a wild-type operon. 
D)  In the absence of tryptophan, RNA polymerase will not bind to the operator/promoter region in the mutant operon. 
E)  In the presence of tryptophan, transcription will be initiated at the second structural gene in the mutant operon. 
A)  In the presence of tryptophan, transcription of the structural genes will be enhanced compared with a wild-type operon. 
B)  In the absence of tryptophan, transcription of the structural genes will be reduced compared with a wild-type operon. 
C)  In the presence of tryptophan, the repressor will bind to the operator/promoter region in the mutant operon more strongly than in a wild-type operon. 
D)  In the absence of tryptophan, RNA polymerase will not bind to the operator/promoter region in the mutant operon. 
E)  In the presence of tryptophan, transcription will be initiated at the second structural gene in the mutant operon.

Question 12

A mutant E. coli strain, grown under conditions that normally induce the lac operon, does not produce ß-galactosidase. What is a possible genotype of the cells?

Accepted Answer

A)  lacI+ lacP+ lacO+ lacZ+ lacY- lacA+ 
B)  lacI+ lacP+ lacOc lacZ+ lacY+ lacA+ 
C)  lacl+ lacP+ lacO+ lacZ+ lacY+ lacA+ 
D)  lacI+ lacP- lacO+ lacZ+ lacY+ lacA+ 
E)  lacI- lacP+ lacO- lacZ+ lacY+ lacA- 
A)  lacI+ lacP+ lacO+ lacZ+ lacY- lacA+ 
B)  lacI+ lacP+ lacOc lacZ+ lacY+ lacA+ 
C)  lacl+ lacP+ lacO+ lacZ+ lacY+ lacA+ 
D)  lacI+ lacP- lacO+ lacZ+ lacY+ lacA+ 
E)  lacI- lacP+ lacO- lacZ+ lacY+ lacA-

Question 13

A mutation occurs in the trp operon DNA of E. coli and results in the change to the two UGG tryptophan codons in the 5' UTR of the RNA to UAG stop codons. What effect will this mutation be expected to have on the regulation of this mutant trp operon compared to a wild-type operon?

Accepted Answer

A)  In the presence of tryptophan, transcription of the structural genes will be reduced compared with a wild-type operon. 
B)  In the absence of tryptophan, transcription of the structural genes will be reduced compared with a wild-type operon. 
C)  In the presence of tryptophan, the repressor will bind to the operator/promoter region with the mutant operon more strongly than with a wild-type operon. 
D)  In the absence of tryptophan, RNA polymerase will not bind to the operator/promoter region with the mutant operon. 
E)  In the presence of tryptophan, transcription of the structural genes will be enhanced compared with a wild-type operon. 
A)  In the presence of tryptophan, transcription of the structural genes will be reduced compared with a wild-type operon. 
B)  In the absence of tryptophan, transcription of the structural genes will be reduced compared with a wild-type operon. 
C)  In the presence of tryptophan, the repressor will bind to the operator/promoter region with the mutant operon more strongly than with a wild-type operon. 
D)  In the absence of tryptophan, RNA polymerase will not bind to the operator/promoter region with the mutant operon. 
E)  In the presence of tryptophan, transcription of the structural genes will be enhanced compared with a wild-type operon.

Question 14

If a mutation prevents the formation of the antiterminator 2+3 loop in the trp operon, what would be the effect?

Accepted Answer

A)  transcription only when tryptophan is absent 
B)  transcription only when tryptophan is present 
C)  constitutive attenuation of transcription 
D)  constitutive transcription 
E)  no effect, as 2+3 loop has no function 
A)  transcription only when tryptophan is absent 
B)  transcription only when tryptophan is present 
C)  constitutive attenuation of transcription 
D)  constitutive transcription 
E)  no effect, as 2+3 loop has no function

Question 15

The 5' UTR of the trp operon RNA contains several UGG tryptophan codons. What would be the effect on transcription-attenuation gene regulation if the trp codons were converted to UGC cysteine codons?

Accepted Answer

The trp operon in bacteria is a classic

Question 16

A lac operon of genotype lacI+ lacP+ lacO+ lacZ- lacY+ will not produce $\beta$-galactosidase but will produce permease when:

Accepted Answer

A)  lactose is present. 
B)  lactose is absent. 
C)  in the presence or absence of lactose. 
D)  glucose is present. 
E)  glucose and lactose are present. 
A)  lactose is present. 
B)  lactose is absent. 
C)  in the presence or absence of lactose. 
D)  glucose is present. 
E)  glucose and lactose are present.

Question 17

Where would the lac repressor be bound in a (nonmutant) E. coli cell that is growing in low glucose and high lactose? (I = lac repressor gene; Z, Y, A = lac operon structural genes; P = lac promoter; O = lac operator)

Accepted Answer

A)  P 
B)  O 
C)  P and O 
D)  I, P, O 
E)  The repressor would not be bound. 
A)  P 
B)  O 
C)  P and O 
D)  I, P, O 
E)  The repressor would not be bound.

Question 18

What is the difference between negative control operons that use induction and systems that use repression?

Accepted Answer

Negative control operons are systems in

Question 19

You have isolated two mutations linked to the lac operon, which you designate Lac1- and Lac2- that cause constitutive expression of the operon. You construct strains carrying a lac operon with a mutant lacY gene on an F'. You test both ß-galactosidase activity and Lac permease activity in the strains you constructed using the artificial inducer IPTG. $$\begin{array}{l}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { B-galactosidase activity Lac permease activity }\
\begin{array} { ccccc } 
& \text { - IPTG}&{+ IPTG } & \text { - IPTG } & \text { + IPTG } \
\mathrm { Lac1 } ^ { - } \operatorname { lac } Z^- \operatorname { lac } Y ^ { + } / \mathrm { F } ^ { \prime } \operatorname { lac } Z ^ { + } \operatorname { lac } Y ^ { - } & - & + & + & + \
\mathrm { Lac2 } ^ { - } \operatorname { lac } Z^- \operatorname { lac } Y ^ { + } / \mathrm { F } ^ { \prime } \operatorname { lac } Z ^ { + } \operatorname { lac } Y ^ { - } & + & + & + & +
\end{array}
\end{array}$$ Are Lac1- and Lac2- dominant or recessive? Do they act in cis or in trans? Indicate how you can determine both of these properties for each mutation. What type of lac mutations best fit the properties of Lac1- and of Lac2-?

Accepted Answer

Lac1^- and Lac2^- ar

Question 20

When a structural gene is under negative inducible control, what would be the result of a mutation that eliminates the repressor protein?

Accepted Answer

A)  The structural gene will be constitutively expressed due to the lack of negative inducible control. 
B)  The transcription of the structural gene will not be affected, as a repressor is not required. 
C)  The mutation will lead to activation of an activator upon the lack of a repressor protein, which will allow the transcription to continue. 
D)  Since transcription will require a repressor protein, the transcription will be turned off. 
E)  More cAMP will be produced in a cell to compensate for the lack of a repressor protein. 
A)  The structural gene will be constitutively expressed due to the lack of negative inducible control. 
B)  The transcription of the structural gene will not be affected, as a repressor is not required. 
C)  The mutation will lead to activation of an activator upon the lack of a repressor protein, which will allow the transcription to continue. 
D)  Since transcription will require a repressor protein, the transcription will be turned off. 
E)  More cAMP will be produced in a cell to compensate for the lack of a repressor protein.

Exam 16: Control of Gene Expression in Prokaryotes

Transcriptional control that acts by regulating the continuation of transcription is called:

Which parts of the DNA region shown in the diagram encode proteins? (I = lac repressor gene; Z, Y, A = lac operon structural genes; P = lac promoter; O = lac operator)

If there are mutations that inactivate lacP and lacI, which of the following statements is true? (I = lac repressor gene; Z, Y, A = lac operon structural genes; P = lac promoter; O = lac operator)

Which of the following is NOT a common DNA-binding motif?

What would happen to the lac operon in the absence of allolactose?

A promoter that affects only genes that are on the same piece of DNA is referred to as a(n) _____-acting promoter.

RNA molecules that are complementary to particular sequences on mRNA are called:

It is possible for a repressor to negatively regulate the expression of an operon because:

A mutant E. coli strain, grown under conditions that normally induce the lac operon, does not produce ß-galactosidase. What is a possible genotype of the cells?

A mutation occurs in the trp operon DNA of E. coli and results in the change to the two UGG tryptophan codons in the 5' UTR of the RNA to UAG stop codons. What effect will this mutation be expected to have on the regulation of this mutant trp operon compared to a wild-type operon?

If a mutation prevents the formation of the antiterminator 2+3 loop in the trp operon, what would be the effect?

The 5' UTR of the trp operon RNA contains several UGG tryptophan codons. What would be the effect on transcription-attenuation gene regulation if the trp codons were converted to UGC cysteine codons?

A lac operon of genotype lacI+ lacP+ lacO+ lacZ- lacY+ will not produce β\betaβ -galactosidase but will produce permease when:

Where would the lac repressor be bound in a (nonmutant) E. coli cell that is growing in low glucose and high lactose? (I = lac repressor gene; Z, Y, A = lac operon structural genes; P = lac promoter; O = lac operator)

What is the difference between negative control operons that use induction and systems that use repression?

When a structural gene is under negative inducible control, what would be the result of a mutation that eliminates the repressor protein?

Introduction to Genetics

Chromosomes and Cellular Reproduction

Basic Principles of Heredity

Sex Determination and Sex-Linked Characteristics

Extensions and Modifications of Basic Principles

Pedigree Analysis, Applications, and Genetic Testing

Linkage, Recombination, and Eukaryotic Gene Mapping

Chromosome Variation

Bacterial and Viral Genetic Systems

DNA: the Chemical Nature of the Gene

Chromosome Structure and Organelle Dna

DNA Replication and Recombination

Transcription

Rna Molecules and Rna Processing

The Genetic Code and Translation

Control of Gene Expression in Eukaryotes

Gene Mutations and Dna Repair

Molecular Genetic Analysis and Biotechnology

Genomics and Proteomics

Epigenetics

Developmental Genetics and Immunogenetics

Cancer Genetics

Quantitative Genetics

Population Genetics

Evolutionary Genetics

Filters

A lac operon of genotype lacI⁺ lacP⁺ lacO⁺ lacZ^- lacY⁺ will not produce $\beta$ -galactosidase but will produce permease when: