Pearson eText Genetic Analysis: An Integrated Approach -- Instant Access (Pearson+)
3rd Edition
ISBN: 9780135564172
Author: Mark Sanders, John Bowman
Publisher: PEARSON+
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Chapter 12, Problem 23P
What is a riboswitch? Describe the riboswitch mechanism that regulates transcription of the thi operon in B. subtilus. What parallels can you see between this mechanism and regulation of transcription of the
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The streptolysin S toxin made by S. pyogenes is encoded by a 9-gene
operon, sagABCDEFGHI. Thinking about what a 3-line diagram would look like for this
operon, answer the following questions. Write numeric answers only. For example, if your
answer is 6 promoters, write only 6.
1) How many promoters control the expression of these genes?
2) How many locations does RNA Polymerase bind to get full expression of these genes?
3) How many ribosome binding sites are needed for full protein expression?
4) How many start codons will be needed for full protein expression?
5) How many mRNA strands will be produced with full operon expression?
6) How many proteins will be produced with full protein expression?
1
What is the phenotype of an E. coli strain with a mutation in the lac operator that allows the lac repressor to irreversibly bind the operator? Assume glucose is absent.
1S
A) O Transcription of the operon is very high whether lactose is present or not.
B) O Transcription of the operon is very low whether lactose is present or not.
C) O Transcription of the operon is high in the presence of lactose, and low in its absence.
D) O Transcription of the operon is low in the presence of lactose, and high in its absence.
Listed in parts a through g are some mutations that were found in the 5′ UTR of the trp operon of E. coli. What will the most likely effect of each of these mutations be on the transcription of the trp structural genes? a. A mutation that prevents the binding of the ribosome to the 5′ end of the mRNA 5′ UTR b. A mutation that changes the Trp codons in region 1 of the mRNA 5′ UTR into codons for alanine c. A mutation that creates a stop codon early in region 1 of the mRNA 5′ UTR d. Deletions in region 2 of the mRNA 5′ UTR e. Deletions in region 3 of the mRNA 5′ UTR f. Deletions in region 4 of the mRNA 5′ UTR g. Deletion of the string of adenine nucleotides that follows region 4 in the 5′ UTR
Chapter 12 Solutions
Pearson eText Genetic Analysis: An Integrated Approach -- Instant Access (Pearson+)
Ch. 12 - 12.1 Bacterial genomes frequently contain groups...Ch. 12 - Transcriptional regulation of operon gene...Ch. 12 - Why is it essential that bacterial cells be able...Ch. 12 - Identify similarities and differences between an...Ch. 12 - The transcription of -galactosidase and permease...Ch. 12 - 12.6 Is attenuation the product of an allosteric...Ch. 12 - The trpL region contains four repeated DNA...Ch. 12 - The CAP binding site in the lac promoter is the...Ch. 12 - What role does cAMP play in transcription of lac...Ch. 12 - How would a cap- mutation that produces an...
Ch. 12 - Explain the circumstances under which attenuation...Ch. 12 - Consider the transcription of genes of the...Ch. 12 - Describe the lytic and lysogenic life cycles of ...Ch. 12 - 12.14 Define antisense RNA, and describe how it...Ch. 12 - 12.15 Attenuation of trp operon transcription is...Ch. 12 - 12.16 In the lac operon, what are the likely...Ch. 12 - Identify which of the following lac operon haploid...Ch. 12 - Prob. 18PCh. 12 - 12.19 List possible genotypes for lac operon...Ch. 12 - Suppose each of the genotypes you listed in parts...Ch. 12 - 12.21 Four independent mutants (mutants A to D)...Ch. 12 - Suppose the lac operon partial diploid...Ch. 12 - What is a riboswitch? Describe the riboswitch...Ch. 12 - 12.24 A repressible operon system, like the trp...Ch. 12 - 12.25 What is the likely effect of each of the...Ch. 12 - 12.26 Suppose that base substitution mutations...Ch. 12 - 12.27 Two different mutations affect. Mutant...Ch. 12 - How would mutations that inactivate each of the...Ch. 12 - The bacterial insertion sequence IS 10 uses...Ch. 12 - For an E. coli strain with the lac operongenotype...Ch. 12 - 12.31 How could antisense RNA be used as an...Ch. 12 - 12.32 Section describes the function of tRNA...Ch. 12 - The following hypothetical genotypes have genes A,...Ch. 12 - 12.34 Northern blot analysis is performed on...Ch. 12 - Prob. 35PCh. 12 - Prob. 36PCh. 12 - 12.37 The electrophoresis gel shown in part (a) is...
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- Which of the following lac operon genotypes would allow for functional versions of all the structural enzymes of the lac operon to be expressed constitutively even in the absence of lactose? Group of answer choices I+ O+ Z+ Y+ A+ I- O+ Z- Y- A- I+ OC Z+ Y+ A+ IS O+ Z+ Y+ A+ I+ O+ Z- Y+ A+arrow_forwardMutation in the regulatory gene in the lac operon results in the formation of an inactive repressor. List and explain the effect of such a mutation on the expression of the structural gene for lactose in E.coli?arrow_forwardTryptophan (Trp) attenuation is an extra mechanism of regulation of trp operon when trp level is too high. Attenuation causes premature transcription termination. a) Propose a solution to overcome a mutated trp codon in the Trp attenuator sequence (domain 1)arrow_forward
- What does the lac operon consist of? How is the operator switch turned on and off in the expression of genes in this operon? Explain.arrow_forwardImagine that a new strain of E. coli is discovered, and it contains the following novel genetic region including the lacI gene and the lac operon: *see image* Upstream of the promoter associated with the lac operon, there is a new operator element "Oν" (O-"nu"). This new operator has high sequence homology to O1, the DNA element that is bound with the highest affinity by the lac repressor. What would be the impact of this new genetic element regarding behavior of the operonin the absence (vs. the presence) of lactose and allolactose? Answer in terms of the protein levels of the lac repressor, as well as the proteins encoded by the genes lacZ/Y/A in the downstream region of the operon. Remember that proteins, once expressed/generated, will not persist forever, and that they have a natural lifetime (ending when they are degraded by the cell).arrow_forwardA strain of E. coli has the genotypes shown below at the lac operon, where I = regulator gene, P = promoter, O = operator, Z = βgalactosidase gene, and Y = permease gene. The superscript+ indicates a wild-type allele,c indicates a constitutive mutation, and− indicates a defective mutation. For each genotype, indicate whether the enzyme will be synthesized or not synthesized when lactose is present or absent by placing a + for synthesis occurring and a − for synthesis not occurring in the appropriate blank. Explain your reasoning for each answer.arrow_forward
- What would happen if the operator sequence of the trp operon contained a mutation that prevented the repressor protein from binding to the operator? (Explain what would happen in both the presence and absence of tryptophan)arrow_forwardSuppose the tRNA synthetase responsible for attaching tryptophan to tRNA is muted in a bacterial strain with the result that the tRNA sythetase functions at twice the efficiency of the wild-type tRNA synthetase. Which of the following is most likely? a)the attenuation mechanism will not function normally and transcriptionof the trp operon will be less dependent upon intracellular tryptophan levels b)the attenuation mechanism will not function normally and transcriptionof the trp operon will be strongly dependent upon intracellular tryptophan levelsarrow_forwardLet’s suppose you have isolated a mutant strain of E. coli in which the lac operon is constitutively expressed. In other words, the operon is turned on in the presence or absence of lactose. One possibility is that the mutation mayblock the transcription of the lacI gene, thereby preventing the synthesis of lac repressor. A second possibility is that the mutation could alter the sequence of the lac operator in a way that prevents lac repressor from binding to the operator. How would you distinguish between these two possibilities?arrow_forward
- Supply the words “off" or “on" in the blanks below: In an inducible operon, transcription is normally and must be turned In a repressible operon, transcription is normally and must be turned Briefly describe the overall function of the structural genes in the lac operon. Briefly describe the overall function of the structural genes in the trp operon. For the following descriptions of the bacterial lac operon, determine if lactose is present (P) or absent (A). The repressor is bound to the operator. The repressor is inactive. RNA polymerase transcribes the structural genes. Allolactose is bound to the repressor For the following descriptions of the bacterial trp operon, determine if tryptophan levels are high (H) or low (L). The repressor is bound to the operator. The repressor is inactive. RNA polymerase transcribes the structural genes. Tryptophan is bound to the repressor.arrow_forwardIn the bacterium,Martian coli, it was discovered that the lac operon is positively regulated. Lactose, when present, binds to the regulatory protein A. The protein A-lactose complex then binds to the operator domain 0 and induces synthesis of lacZ+ and lacY+ MRNAS. a) What would be the most common phenotype of o- mutants in terms of lactose utilization? Explain your answer. b) What would be the most common phenotype of A- mutants? Explain your answer.arrow_forwardA number of mutations affect the expression of the lac operon in E. coli. The genotypes of several E. coli strains are shown below. ("+" indicates a wild-type gene with normal function and "-" indicates a loss-of-function allele.) Please predict which of the following strains would have the lowest beta-galactosidase enzyme activity, when grown in the lactose medium. Orpt o* z* r* Orpt ot z* Y OrptoztY Orrotzr OrPotz*Yarrow_forward
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