Chapter 16

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? 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.

A lac operon of genotype lacI+ lacP+ lacO+ lacZ+ lacY- will produce -galactosidase but not permease when: 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 both present.

A) lactose is present.

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

The trp operon in E. coli contains a 5′ UTR sequence that is translated into a small polypeptide of 14 amino acids, which includes two tryptophans. If the two trp codons in the 5′ UTR of the RNA are changed to serine codons and the resulting cells are starved for tryptophan but not for any other amino acid, what will be the effect of the mutant codons on the operation of the trp operon? A) The trp repressor will be synthesized in greater amounts. B) Expression of the trp structural genes will be less than with a normal trp operon. C) Expression of the trp structural genes will be greater than with a normal trp operon. D) The leader polypeptide will not be synthesized. E) The expression of the operon will not be affected by these mutations.

B) Expression of the trp structural genes will be less than with a normal trp operon.

In the presence of both lactose and glucose, which of the following occurs with the E. coli lac operon? A) The lacI gene does not produce repressor. B) The cAMP-CAP complex is not available to bind near or at the lac promoter. C) The lacZ and lacY genes are fully expressed. D) Lactose is converted to glucose and galactose. E) Lactose binds to the operator.

B) The cAMP-CAP complex is not available to bind near or at the lac promoter.

35. Suppose that you perform an experiment where you construct a plasmid that carries a copy of the lac operator region (lacO) but no other part of the lac operon. (The lac repressor can bind to single operator regions.) This plasmid is placed in an E. coli cell, which has a normal copy of the lac operon in its chromosome. When this strain is grown, the number of plasmids reaches about 50 copies per bacterial cell. What is the expected phenotype of such a strain in the absence of glucose? A) The lac operon will be turned on even in the absence of lactose. B) The lac operon will be turned off even in the presence of lactose. C) The lac operon will be regulated normally. D) The lac operon will be initially turned on in the presence of lactose but eventually it will be turned off even though lactose is still present. E) The lac operon will be expressed only if galactose is added to the Moderate.

B) The lac operon will be turned off even in the presence of lactose.

A partial diploid E. coli cell of lacI+ lacP- lacOc lacI+ lacY+ / lacIs lacP+lacO+ lacZ+ lacY- will synthesize: A) both lacZ and lacY functional gene products in the absence of lactose. B) neither lacZ nor lacY functional gene products in the presence of lactose. C) both lacZ and lacY functional gene products in the presence of lactose. D) lacY but not a functional lacZ gene product in the absence of lactose. E) lacZ but not a functional lacY gene product in the absence of lactose.

B) neither lacZ nor lacY functional gene products in the presence of lactose.

Which of the following is NOT a common DNA-binding 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

B) the beta sheet-alpha helix motif

There are enzymes called aminoacyl-tRNA synthetases that attach tRNAs to the appropriate amino acid. Assume that the aminoacyl-tRNA synthetase that attaches tryptophan to its tRNA in an E. coli mutant strain is only partially active. It is active enough for the strain that carries it to be viable but is much less active than that of wild-type cells. What would be the expected effect of this mutation on attenuation in the trp operon? A) Pairing of regions 3 and 4 in the 5′ UTR of the RNA will be enhanced so attenuation will increase in the presence of tryptophan. B) Pairing of regions 2 and 3 in the 5′ UTR of the RNA will be decreased so attenuation will increase in the presence of tryptophan. C) Pairing of regions 3 and 4 in the 5′ UTR of the RNA will be decreased so attenuation will decrease in the presence of tryptophan. D) Attenuation will not change but the trp repressor will be more active and the transcription of the trp operon structural genes will be decreased in the presence of tryptophan. E) Attenuation will be decreased in the absence of tryptophan but will be enhanced in the presence of tryptophan.

C) Pairing of regions 3 and 4 in the 5′ UTR of the RNA will be decreased so attenuation will decrease in the presence of tryptophan.

Assume that a mutation occurs in the promoter for the lacI regulatory gene and this mutation results in a tenfold increase in the transcription of lacI. What would be the expected consequences of such a mutation? A) The lac structural genes will be fully expressed even in the presence of glucose and absence of lactose. B) The lac operon would be expected to be regulated normally. C) The lac structural genes will not be fully induced even in the absence of glucose and presence of lactose. D) The lac structural genes will be partially expressed in the presence of glucose and fully expressed if lactose is also present. E) The lac structural genes will now be fully expressed in the absence of glucose and lactose but not expressed in the absence of glucose and presence of lactose.

C) The lac structural genes will not be fully induced even in the absence of glucose and presence of lactose.

A lac operon of genotype lacI- lacP+ lacO+ lacZ+ lacY+ will produce -galactosidase and permease when: A) lactose is present. B) lactose is absent. C) lactose is present or not. D) glucose is present. E) glucose and lactose are both present.

C) lactose is present or not.

A mutant E. coli strain is found that synthesizes -galactosidase in the absence of glucose whether or not lactose is present. What two mutations might lead to this outcome? A) lacIs mutation or lacOc mutation B) lacP- mutation or lacI- mutation C) lacP- mutation or lacOc mutation D) lacI- mutation or lacOc mutation E) lacP- mutation or lacIs mutation

D) lacI- mutation or lacOc mutation

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? 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.

E) In the presence of tryptophan, transcription of the structural genes will be enhanced compared with a wild-type operon.

Which of the following E. coli strains will synthesize permease in the presence of lactose and absence of glucose? A) lacI- lacP- lacO+ lacZ+ lacY+ B) lacIs lacP- lacO+ lacZ- lacY+/lacI+ lacP+ lacO+ lacZ+ lacY+ C) lacI- lacP+ lacO+ lacZ+ lacY- D) lacI- lacP+ lacOc lacZ-lacY-/lacI+ lacP- lacO+ lacZ- lacY+ E) lacI+ lacP+ lacOc lacZ+ lacY-/lacI- lacP+ lacO+lacZ- lacY+

E) lacI+ lacP+ lacOc lacZ+ lacY-/lacI- lacP+ lacO+lacZ- lacY+

A partial diploid E. coli cell of lacI+lacP+lacOc lacZ-lacY-/ lacI- lacP+ lacO+lacZ-lacY+ genotype will synthesize: A) both lacZ and lacY gene products in the absence of lactose. B) neither lacZ nor lacY gene products in the presence of lactose. C) lacZ but not lacY gene product in the presence of lactose. D) lacY but not lacZ gene product in the absence of lactose. E) lacY but not lacZ gene product in the presence of lactose.

E) lacY but not lacZ gene product in the presence of lactose.

Which of the following types of eukaryotic gene regulation is at the level of DNA? a. Alternation of chromatin structure b. mRNA processing c. RNA interference d. mRNA stability e. Post-translational modification

a. Alternation of chromatin structure

What is the function of allolactose in regulation of the lac operon? a. Inducer b. Repressor c. Activator d. Promoter e. Regulatory protein

a. Inducer

When a structural gene is under negative inducible control, what would be the result of a mutation that eliminates the 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. As the 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.

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

A promoter that affects only genes that are on the same piece of DNA is referred to as a ____-acting promoter. a. cis b. trans c. enhancer d. positive e. negative

a. cis

Proteins with DNA binding motifs predominantly bind to the ____________ of DNA. a. major grooves b. minor grooves c. paired nitrogenous bases d. phosphate groups e. deoxyribose sugar

a. major grooves

An operon is controlled by a repressor. When the repressor binds to a small molecule, it is released from binding to DNA near the operon. The operon is never expressed if a mutation prevents the repressor from binding to the small molecule. The type of control illustrated is a. negative inducible. b. negative repressible. c. positive inducible. d. positive repressible. e. attenuation.

a. negative inducible.

E. coli lac operon control by lacI is a. negative inducible. b. negative repressible. c. positive inducible. d. positive repressible. e. attenuation.

a. negative inducible.

Which of the following statements about gene regulation concerning operon is INCORRECT? a. A repressible gene is controlled by a regulatory protein that inhibits transcription. b. For a gene under negative repressible control, a small molecule is required to prevent the gene's repressor from binding to DNA. c. For a gene under positive repressible control, the normal state is transcription of a gene, stimulated by a transcriptional activator. d. A regulator gene has its own promoter and is transcribed into an independent mRNA. e. Presence of operon where genes of related functions are clustered is common in bacteria, but not in eukaryotes.

b. For a gene under negative repressible control, a small molecule is required to prevent the gene's repressor from binding to DNA.

What is the function of cAMP in regulation of the lac operon? a. It activates a repressor protein. b. It activates an activator protein. c. It inactivates a repressor protein. d. It inactivates an activator protein. e. It causes attenuation.

b. It activates an activator protein.

Which of the following generally get transcribed constitutively? a. Regulatory gene b. Structural gene c. Operator element d. Promoter element e. Operon

b. Structural gene

In the absence of tryptophan, what happens to the genes within the trp operon? a. The regulator without tryptophan-binding prevents the genes from being transcribed. b. The regulator falls off the operator and structural genes get transcribed. c. Lack of tryptophan increases the level of cAMP high, which leads to activation of CAP protein and gene expression. d. The active repressor binds to the operator and genes do not get transcribed. e. The active activator binds to the operator and transcription of structural gene takes place.

b. The regulator falls off the operator and structural genes get transcribed.

When binding of the inducer to the repressor causes a conformational change, which then prevents the repressor from binding to DNA, the repressor is called a(n) __________ protein. a. coactivator b. allosteric c. structural d. operating e. responsive

b. allosteric

A mutant E. coli strain, grown under conditions that normally induce the lac operon, produces high amounts of ß-galactosidase. What is a possible genotype of the cells? a. lacI+ lacP+ lacO+ lacZ- lacY+ lacA+ b. lacI+ lacP+ lacOc lacZ+ lacY+ lacA+ c. lacI- lacP+ lacO+ lacZ- lacY+ lacA+ d. lacI+ lacP- lacO+ lacZ+ lacY+ lacA+ e. lacI- lacP- lacO+ lacZ- lacY+ lacA-

b. lacI+ lacP+ lacOc lacZ+ lacY+ lacA+

An operon is controlled by a repressor. When the repressor binds to a small molecule, it binds to DNA near the operon. The operon is constitutively expressed if a mutation prevents the repressor from binding to the small molecule. The type of control illustrated is a. negative inducible. b. negative repressible. c. positive inducible. d. positive repressible. e. catabolite repression

b. negative repressible.

The________ is a type of regulator protein that binds to a region of DNA in the promoter of a gene called the operator and prevents transcription from taking place. a. inducer b. repressor c. activator d. inactivator e. terminator

b. repressor

The formation of 1+2 and 3+4 secondary structures of 5′ UTR region mRNA from the trp operon is triggered when a. the tryptophan level inside the bacterial cell is extremely low. b. the tryptophan level inside the bacterial cell is high. c. the repressor protein fails to bind to the operator. d. there is a spontaneous mutation introduced into the 5′ UTR. e. the structural gene transcription within the trp operon gets initiated.

b. the tryptophan level inside the bacterial cell is high.

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

c. Constitutive attenuation of transcription

Which of the following DNA binding motifs are composed of three alpha helices? a. Zinc-finger b. Leucine-zipper c. Homeodomain d. Helix-turn-helix e. Helix-loop-helix

c. Homeodomain

What would happen to the lac operon in the absence of allolactose? a. The structural genes within the lac operon the 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.

c. The repressor regulator protein binds to the operator and prevents the transcription of the structural gene.

RNA molecules that are complementary to particular sequence on mRNA are called a. complementary RNA. b. sense RNA. c. antisense RNA. d. riboswitches. e. ribozymes.

c. antisense RNA.

11. E. coli lac operon control by CAP is a. negative inducible. b. negative repressible. c. positive inducible. d. positive repressible. e. regulated by riboswitches.

c. positive inducible.

An example of a gene product encoded by a regulatory gene is a. beta-galactosidase enzyme. b. allolactose. c. repressor protein. d. an operator. e. a terminator.

c. repressor protein.

It is possible for a repressor to negatively regulate the expression of an operon because 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, hence preventing the transcription. e. the repressor physically blocks where the activator should be binding on the operator region.

c. the repressor-binding site overlaps the promoter site of the operon, allowing it to physically block the binding of RNA polymerase.

When a structural gene is under positive inducible control, what would be the result of a mutation that eliminates the activator protein? a. The structural gene to be constitutively expressed due to the lack of inducible control. b. The transcription of structural gene will not be affected, as an activator is not required. c. The mutation will lead to activation of a repressor upon the lack of an activator protein, which will block transcription. d. As the transcription will require an activator protein, the transcription will be turned off. e. More cAMP will be produced in a cell to compensate for the lack of an activator protein.

d. As the transcription will require an activator protein, the transcription will be turned off.

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) 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. I, Z, Y, A

The trp operon is known to operate by both negative repressible regulation of operator and attenuation. Which of the following does NOT support the reason as to why dual control exists to regulate the operon? a. The repression alone is never complete, and some transcription can be initiated. b. Combined mechanism provides a much finer tuning of tryptophan synthesis regulation. c. Attenuation and repression allow the cell to more sensitively respond to the tryptophan level. d. It is most likely due to the fact that the attenuation is the evolutionary relic, which by accident has remained. e. Repression responds to the cellular levels of tryptophan, while attenuation responds to the number of tRNA charged with tryptophan.

d. It is most likely due to the fact that the attenuation is the evolutionary relic, which by accident has remained.

Which of the following facts about riboswitches is INCORRECT? a. Binding of certain molecules to the riboswitches results in the formation of specific secondary structures of mRNA. b. Certain molecules that bind to riboswitches may act as repressors or inducers of transcription. c. Riboswitches are only found in bacterial cells but not in archaeal, fungal, or plant cells. d. Riboswitches are typically found in the 3′ UTR of the mRNA structure. e. The secondary structure that forms riboswitches typically contains a base stem and several branching hairpins.

d. Riboswitches are typically found in the 3′ UTR of the mRNA structure.

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. 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-

d. lacI+ lacP- lacO+ lacZ+ lacY+ lacA+

Which of the following secondary structures causes attenuation of structural genes of the trp operon? a. 1+2 b. 1+3 c. 2+4 d. 2+3 e. 3+4

e. 3+4

Which of the following statements about DNA binding protein is NOT true? a. Specific amino acids within the motif form hydrogen bonds with DNA. b. These proteins can affect the expression of a gene. c. Most DNA binding proteins bind dynamically. d. Some of these proteins incorporate metal ion such as zinc. e. Once bound, most of DNA binding proteins remain on DNA permanently.

e. Once bound, most of DNA binding proteins remain on DNA permanently.

Which of the following statement about regulation of gene expression is correct? a. An inducible gene is transcribed when a specific substance is absent. b. A gene is any DNA sequence that is transcribed into an mRNA molecule only. c. All genes are transcribed at all times as long as they have a functional promoter. d. The regulation of gene expression is the same in both eukaryotes and prokaryotes. e. The regulation of gene expression is critical for the control of life processes in all organisms.

e. The regulation of gene expression is critical for the control of life processes in all organisms.

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) a. P b. O c. P and O d. I, P, O e. The repressor would not be bound.

e. The repressor would not be bound.

Transcriptional control that acts by regulating the continuation of transcription is called a. riboswitching. b. antitermination. c. negative control. d. operator mutation. e. attenuation.

e. attenuation.

RNA-mediated repression is carried out by a. nonsense RNA. b. sense RNA. c. antisense RNA. d. riboswitches. e. ribozymes.

e. ribozymes.