Genetic Analysis: An Integrated Approach (3rd Edition)
3rd Edition
ISBN: 9780134605173
Author: Mark F. Sanders, John L. Bowman
Publisher: PEARSON
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Chapter 12, Problem 24P
A repressible operon system, like the trpoperon, contains three genes, G, Z, and W. Operon genes are synthesized when the end product of the operon synthesis pathway is absent, but there is no synthesis when the end product is present. One of these genes is an operator, one is a regulatory protein, and the other is a structural enzyme involved in synthesis of the endproduct. In the table below,
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Operon X produces three enzymes that convert Compound A to Compound B. The R gene makes the regulatory molecule for Operon X. Normally, the three enzymes are only produced when Compound B is present. However, when the R gene is mutated (no R gene is made), none of the three enzymes are produced regardless of whether Compount B is absent or present. Is this opern inducible or repressible? Does the R gene produce an activator or repressor? Is the R protein made in an active or inactive form?
Which of the following describes the lac operon in E. coli when lactose and glucose is present in the culture medium?
Select one:
a. CAP inactive and RNA polymerase does not completely bind to the promoter of the lac operon and transcription of lactose-metabolizing enzymes decreases.
b. CAP is active and RNA polymerase binds completely to the promoter of the lac operon and transcription of lactose-metabolizing enzymes decreases.
c. Catabolite activator protein (CAP) inactive and RNA polymerase does not completely bind to the promoter of the lac operon and transcription of lactose-metabolizing enzymes increases.
d. CAP is active and RNA polymerase binds completely to the promoter of the lac operon and transcription of lactose-metabolizing enzymes increases.
In the lac operon, the lacZ gene codes for an enzyme called ____________, which catalyze the breakdown of the sugar __________ into monosaccharides. This enzyme can also hydrolyze the sugar analog ____________, which produces blue pigments following its breakdown. Since the lac operon is not always on the bacterial cells, we add the chemical ________ which prevents the lac depressor from binding to the operators, leading to constitutive expression of the operon.
Chapter 12 Solutions
Genetic Analysis: An Integrated Approach (3rd Edition)
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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- A mutation that inactivates the repressor gene of the lac operon results in (a) the continuous transcription of the structural genes (b) no transcription of the structural genes (c) the binding of the repressor to the operator (d) no production of RNA polymerase (e) no difference in the rate of transcriptionarrow_forwardThe lac operon produces enzymes that allow the bacteria E. coli to metabolize lactose, it is in an inducable operon. When lactose is present, will the repressor protein attach or leave the operon? How would this effect the production of lactose producing enzymes?arrow_forwardWhich of the following statements about the trp operon is false? If a mutation in region 2 prevents the formation of the 2 + 3 loop in the 5’UTR transcription levels will increase. The trp operon is an example of negative repressible operon. Formation of the anti-terminator in the 5’UTR of the trp operon occurs when trp levels are low. In the presence of high trp-tRNA, the genes of the trp operon are not expressed. The role of trp is to bind to the repressor protein and activate it.arrow_forward
- In the presence of lactose and the promoter sequence was mutated such that the RNA polymerase can no longer bind, the structural genes will:[ Select ] ["No longer be expressed", "Be constantly expressed", "Be deleted from the operon"] In the absence of lactose and the lacI repressor gene is mutated such that the repressor protein product can no longer bind to the operator, the structural genes will: [ Select ] ["No longer be expressed", "Be constantly expressed", "Be deleted from the operon"] In the presence of lactose and the lacI repressor gene is mutated such that the repressor protein product can no longer bind to the operator, the structural genes will: [ Select ] ["No longer be expressed", "Be constantly expressed", "Be deleted from the operon"]arrow_forwardYou have isolated different mutants (reg1 and reg2) causing constitutive expression of the emu operon (which has genes emu1 and emu2). One mutant contains a defect in a DNA-binding site, and the other has a loss-of-function defect in the gene encoding a protein that binds to the site Say you don’t know which mutant has a defect in the site and which one has a mutation in the binding protein. To figure it out, you construct the two partial diploid strains (i and ii below), and you then assay the levels of the Emu1 and Emu2 proteins in these two strains. F’ (reg1- reg2+ emu1- emu2+) / reg1+ reg2+ emu1+ emu2- F’ (reg1+ reg2- emu1- emu2+) / reg1+ reg2+ emu1+ emu2- What proteins do you predict will be expressed for strains i and ii if reg2 encodes the regulatory protein and reg1 is the regulatory site?arrow_forwardA mutation occurs in the 5′ UTR of the trp operon that reduces the ability of region 2 to pair with region 3. What will the effect of this mutation be when the tryptophan level is high? When the tryptophan level is low?arrow_forward
- The figure above shows the structure of lac operon. Which of the following BEST describes what happens in the presence of lactose? Select one: Repressor-lactose complex forms, both the complex and RNA polymerase bind to R. Transcription of S is initiated. Repressor-lactose complex forms and the complex will not bind to R. Transcription of S is initiated. Both repressor and RNA polymerase bind to R. Transcription of S is initiated. Repressor-lactose complex forms and the complex binds to R. Transcription of S is prevented.arrow_forwardIn the presence of tryptophan and the promoter sequence was mutated such that the RNA polymerase can no longer bind, the structural genes will:[ Select ] ["No longer be expressed", "Be constantly expressed", "Be deleted from the operon"] In the absence of tryptophan and the trpR repressor gene is mutated such that the repressor protein product can no longer bind to the operator, the structural genes will:[ Select ] ["No longer be expressed", "Be constantly expressed", "Be deleted from the operon"] In the presence of tryptophan and the trpR repressor gene is mutated such that the repressor protein product can no longer bind to the operator, the structural genes will:[ Select ] ["No longer be expressed", "Be constantly expressed", "Be constantly expressed"]arrow_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 may block 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 operon in a way that prevents the repressor protein from binding to the operator. How would you distinguish between these two possibilities?arrow_forward
- Imagine 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_forwardAn E. coli cell acquires a mutation in the gene that encodes CAP. The mutation affects the DNA-binding domain of CAP and ablates the ability of CAP to bind to the CAP site. Under which condition will the genes of the lac operon be transcribed at high levels? Glucose absent, lactose absent Glucose absent, lactose present Glucose present, lactose absent Glucose present, lactose present Under any of these conditions, the lac operon will not be transcribed at high levelsarrow_forwardThe lac operon of E. coli controls the expression of genes that code for enzymes involved in lactose metabolism. Mutations to various regions of the lac operon have been discovered which affect both the control of gene expression and the function of the gene products. These mutations include: I - = produces a repressor protein that cannot bind to the operator region IS = produces a repressor protein that cannot be removed from the operator region OC = cannot bind a repressor protein Z - = produces a defective (non-functioning) β-galactosidase enzyme + = wild type Detail the functionality of the lac operon under the following genetic and cellular conditions. You do not need to consider the role of CAP in your analysis. Genes Repressed (yes/no) Constitutive (yes/no) IS O+ Z+ IS OC Z+arrow_forward
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