Chapter 20 - Mo Bio

Which of the following is not true of the λ repressor protein, cI? A. It binds DNA as a monomeric protein. B. It is inactivated by autocleavage through interaction with RecA protein. C. When bound to OR2 it activates transcription from PPM. D. It represses the transcription of early genes necessary for lytic growth.

A. It binds DNA as a monomeric protein.

Which of the following characteristics of the lactose operon is not true of the galactose operon? A. Repressor binding prevents RNA polymerase from binding to the promoter. B. CRP activates expression when bound to cAMP. C. Expression is high when glucose levels are low and the activating metabolite is present. D. Expression is low when glucose levels are high.

A. Repressor binding prevents RNA polymerase from binding to the promoter.

A merodiploid is: A. a haploid organism that contains a second copy of a part of its genome. B. a haploid organism that is missing part of its genome. C. a diploid organism that is missing part of its genome. D. a diploid organism that contains another copy of its genome.

A. a haploid organism that contains a second copy of a part of its genome.

The result obtained in Jacob and Monod's merodiploid analysis that suggested the lacI region acts in trans to regulate the lac operon was: A. a nonfunctional lacI mutant is rescued by a wild-type lacI allele. B. a nonfunctional lacI mutant cannot be rescued by a wild-type lacI allele. C. a nonfunctional lacO mutant is rescued by a wild-type lacO allele. D. a nonfunctional lacO mutant cannot be rescued by a wild-type lacO allele.

A. a nonfunctional lacI mutant is rescued by a wild-type lacI allele.

The stringent response in bacteria is transcriptional regulation coordinated with: A. amino acid concentrations. B. availability of glucose. C. DNA damage. D. changes in pH.

A. amino acid concentrations.

The LexA protein is: A. the repressor of the SOS response. B. the coprotease for the cleavage of RecA protein. C. a DNA repair enzyme. D. a regulatory protein for the lac operon.

A. the repressor of the SOS response.

Which one of the following proteins is not required at low, basal levels for the regulation of the expression of the lac operon? A. thiogalactoside transacetylase B. galactoside permease C. β-galactosidase

A. thiogalactoside transacetylase

Ribosomal proteins that can act as translational repressors: A. are not encoded by the same mRNA that they repress. B. bind to a site on the mRNA near the start site of one gene in the operon. C. bind to mRNA with higher affinity than to the appropriate rRNA molecule. D. bind to the mRNA when sensing that levels of r-protein are low relative to rRNA.

B. bind to a site on the mRNA near the start site of one gene in the operon.

How does cAMP affect the expression of the lac operon? A. cAMP binds to the CRP, decreasing its affinity for a DNA site near the promoter. B. cAMP binds to the CRP, increasing its affinity for a DNA site near the promoter. C. cAMP binds to the Lac repressor, decreasing its affinity for a DNA site near the promoter. D. cAMP binds to the Lac repressor, increasing its affinity for a DNA site near the promoter.

B. cAMP binds to the CRP, increasing its affinity for a DNA site near the promoter.

Which protein(s), A, B, C, and/or D, appear to bind to the CRP-binding site? A. proteins B and C B. proteins A and D C. protein A only D. protein B only

B. proteins A and D

A riboswitch mechanism is known to regulate the transcription of genes involved in: A. lactose metabolism. B. vitamin B1 synthesis. C. tryptophan biosynthesis. D. arabinose metabolism.

B. vitamin B1 synthesis.

Which of the following is nottrue of the lacI region of the lac operon? A. It is transcribed separately from the operon. B. It produces a diffusible product that can regulate the expression of the operon. C. It is bound by the Lac repressor when lactose is unavailable. D. Its mutation leads to constitutive expression of the operon.

C. It is bound by the Lac repressor when lactose is unavailable.

Which of the following describes the function of the lacO region of the lac operon? A. It encodes for the Lac repressor protein. B. It contains the promoter for the operon. C. Mutation of this region leads to constitutive expression of the operon. D. It encodes for the galactoside permease protein.

C. Mutation of this region leads to constitutive expression of the operon.

Upon the initial infection of a host cell by bacteriophage λ, the first two proteins produced from expression of the phage genome are: A. cI and cII. B. N and cI. C. N and Cro. D. Cro and cI.

C. N and Cro.

Which of the following is the most likely explanation for the band pattern seen in lane 6? A. Protein D is a restriction enzyme and cut the DNA fragment into two DNA fragments. B. Protein D binding to the CRP-binding site is less tight compared to cAMP-CRP binding. C. Protein D has a smaller mass than the cAMP-CRP protein. D. Protein D removed radioactive label from the DNA fragment.

C. Protein D has a smaller mass than the cAMP-CRP protein.

How does the RecA protein contribute to the increased expression of SOS genes? A. RecA protein competes with LexA protein for binding to the operator sequences. B. RecA protein binds to LexA protein bound to the operator, directly lowering the affinity of LexA protein for DNA. C. RecA protein binds to free LexA protein, mediating the self-cleavage of the repressor. D. RecA protein binding to the promoter region recruits RNA polymerase.

C. RecA protein binds to free LexA protein, mediating the self-cleavage of the repressor.

Which of the following characteristics of the glmS riboswitch is also true of the TPP riboswitch? A. The glmS riboswitch is a ribozyme. B. The structure of the riboswitch is the same, whether bound by ligand or not. C. The riboswitch lowers the rate of translation when bound to its metabolite ligand.

C. The riboswitch lowers the rate of translation when bound to its metabolite ligand.

The products of the hydrolysis of lactose by β-galactosidase are: A. galactose and allolactose. B. glucose and allolactose. C. galactose and glucose. D. glucose and ribose.

C. galactose and glucose.

Catabolite repression of the lac operon restricts expression when: A. glucose is absent. B. lactose is absent. C. glucose is present. D. lactose is present.

C. glucose is present.

The Lac repressor protein binds to the: A. operator in the presence of allolactose. B. lacZ gene in the presence of allolactose. C. operator in the absence of allolactose. D. operator regardless of the presence or absence of allolactose.

C. operator in the absence of allolactose.

Which of the following is true of the structure of the TPP riboswitch only when bound to thiamine pyrophosphate? A. The conformation of the riboswitch allows the ribosome to access the Shine-Dalgarno sequence. B. The riboswitch folding creates a binding site for the ribosome. C. The riboswitch RNA becomes catalytically active to cleave mRNA. D. The riboswitch is less susceptible to cleavage by ribonuclease.

D. The riboswitch is less susceptible to cleavage by ribonuclease.

Which of the following is not true of the three operators of the lac operon? A. One of the operators is contained within the lacZ gene. B. All three operators are bound simultaneously by the Lac repressor to repress the expression of the operon. C. The DNA between the operators bound by the Lac repressor is looped out to sterically hinder RNA polymerase. D. Two of the three operators are upstream of the transcriptional start site.

B. All three operators are bound simultaneously by the Lac repressor to repress the expression of the operon.

Which of the following events represses the expression of the bacteriophage λ cI gene? A. activation of PRE by cII protein B. Cro protein binding to the OR3 operator C. multiple viral particles infecting a single cell D. cIII protein protecting cII from proteolysis

B. Cro protein binding to the OR3 operator

Which of the following is not true of the lacO region of the lac operon? A. It is the operator of the operon. B. It produces a diffusible product that can regulate the expression of the operon. C. It is bound by the Lac repressor when lactose is unavailable. D. Its mutation leads to constitutive expression of the operon.

B. It produces a diffusible product that can regulate the expression of the operon.

Which of the following is not a cellular response to amino acid starvation in E. coli? A. Levels of guanine tetraphosphate rise. B. Levels of cAMP decrease. C. The transcription of genes needed for rapid growth decreases. D. rRNA synthesis is decreased.

B. Levels of cAMP decrease.

Which of the following is not true of the lac operon? A. Transcription produces a single polycistronic mRNA containing the lacZ, lacY, and lacA genes. B. The lacI gene is controlled from the same promoter as the lacZ gene. C. The Lac repressor protein is constitutively expressed. D. The operator region regulates transcription through interaction with the Lac repressor protein.

B. The lacI gene is controlled from the same promoter as the lacZ gene.

Which of the following is not a characteristic of a riboswitch? A. They are structures that can form in the 5' untranslated region of some mRNA molecules. B. They exert gene expression control only at the level of translation. C. They may physically bind to small-molecule metabolites. D. Ligand-binding to a riboswitch may sequester the Shine-Dalgarno sequence.

B. They exert gene expression control only at the level of translation.

The binding of tryptophan to the Trp repressor protein results in: A. the dissociation of the repressor from the operator sequence. B. a conformational change in the repressor that allows the repressor to bind the operator. C. the recruitment of RNA polymerase. D. an increase in the expression of tryptophan biosynthetic enzymes.

B. a conformational change in the repressor that allows the repressor to bind the operator.

The result obtained in Jacob and Monod's merodiploid analysis that suggested the lacO region acts in cis to regulate the lac operon was: A. a nonfunctional lacI mutant is rescued by a wild-type lacI allele. B. a nonfunctional lacI mutant cannot be rescued by a wild-type lacI allele. C. a nonfunctional lacO mutant is rescued by a wild-type lacO allele. D. a nonfunctional lacO mutant cannot be rescued by a wild-type lacO allele.

D. a nonfunctional lacO mutant cannot be rescued by a wild-type lacO allele.

The binding of _______________ to the Lac repressor causes the protein to dissociate from the operator. A. lactose B. glucose C. fructose D. allolactose

D. allolactose

The protein that represses the lytic genes of bacteriophage λ is: A. Cro. B. N. C. LexA. D. cI.

D. cI.

Which of the following scenarios leads to the highest level of lac operon expression? A. high glucose levels, lactose absent B. low glucose levels, lactose absent C. high glucose levels, lactose present D. low glucose levels, lactose present

D. low glucose levels, lactose present

Which of the following is not true of the stringent response? A. Uncharged tRNA binds to the A site of the ribosome. B. Stringent factor binds to the ribosome. C. ppGpp nucleotide is synthesized in two steps. D. ppGpp binding to the ribosome increases rRNA gene expression.

D. ppGpp binding to the ribosome increases rRNA gene expression.

The enzyme that catalyzes the formation of allolactose from lactose is: A. galactoside permease. B. lactose isomerase. C. thiogalactoside tranacetylase. D. β-galactosidase.

D. β-galactosidase.