Geneticists isolated six trains of E. coli (strains 1-6) whose lac operons had one of the following mutations (a-f): a. deletion of lacY b. oº mutation c. missense mutation in lacz d. inversion of the lac operon (which does not include the lacl gene) e. superrepressor mutation f. inversion of lacz, Y, and Z, but not lacl, P, o Focusing on the mutation in B: a. what is the state of the lac operon (on, off, inducible, or constitutive)? b. Provide an explanation using repressor, RNA pol, transcription, and the appropriate regulatory region of the operon. c. If a PDNA of another lac operon is inserted into the bacteria with a wild type/normal copy of the DNA, how would this impact the transcription of the original mutant in B?

Geneticists isolated six trains of E. coli (strains 1-6) whose lac operons had one of the following mutations (a-f): a. deletion of lacY b. oº mutation c. missense mutation in lacz d. inversion of the lac operon (which does not include the lacl gene) e. superrepressor mutation f. inversion of lacz, Y, and Z, but not lacl, P, o Focusing on the mutation in B: a. what is the state of the lac operon (on, off, inducible, or constitutive)? b. Provide an explanation using repressor, RNA pol, transcription, and the appropriate regulatory region of the operon. c. If a PDNA of another lac operon is inserted into the bacteria with a wild type/normal copy of the DNA, how would this impact the transcription of the original mutant in B?

Name: Geneticists isolated six trains of E. coli (strains 1-6) whose lac op
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Description: Geneticists isolated six trains of E. coli (strains 1-6) whose lac operons had one of thefollowing mutations (a-f):a. deletion of lacYb. oº mutationc. missense mutation in laczd. inversion of the lac operon (which does not include the lacl gene)e. s

Biology (MindTap Course List)

11th Edition

ISBN:9781337392938

Author:Eldra Solomon, Charles Martin, Diana W. Martin, Linda R. Berg

Publisher:Eldra Solomon, Charles Martin, Diana W. Martin, Linda R. Berg

Chapter14: Gene Regulation

Section: Chapter Questions

Problem 9TYU: A mutation that inactivates the repressor gene of the lac operon results in (a) the continuous...

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Which of the following statements uses the term homologous correctly?A. The two X chromosomes in female mammalian cells are homologousto each other.B. The α-tubulin gene in Saccharomyces cerevisiae is homologousto the α-tubulin gene in Arabidopsis thaliana.C. The promoter of the lac operon is homologous to the promoterof the trp operon.D. The lacY genes of E. coli and K. pneumoniae are approximately60% homologous to each other.
a. Some antibiotics, such as rifampin, interfere with the function of RNA polymerase. What biological process is rifampin disrupting? b. Some antibiotic-resistant M. tuberculosis bacteria have a single point mutation (CàT) in the rpoB gene that causes an amino acid change from serine (a polar amino acid) to leucine (a non-polar amino acid). What type of mutation is this? Do you expect this to have no effect, a small effect, or a large effect on the polypeptide produced? Explain your reasoning. c. The rpoB gene encodes a subunit of the bacterial RNA polymerase protein. The point mutation described in Question 2 causes a change in protein folding, which leads to the inability of the rifampin antibiotic to bind to the RNA polymerase. Which level(s) of protein structure is/are affected by this change?
You have isolated two different mutants (reg1 andreg2) causing constitutive expression of the emu operon (emu1 emu2). One mutant contains a defect in aDNA-binding site, and the other has a loss-of-functiondefect in the gene encoding a protein that binds tothe site.a. Is the DNA-binding protein a positive or negativeregulator of gene expression?b. To determine which mutant has a defect in the siteand which one has a mutation in the binding protein, you decide to do an analysis using F′ plasmids. Assuming you can assay levels of the Emu1and Emu2 proteins, what results do you predict forthe two strains (i and ii; see descriptions below) ifreg2 encodes the regulatory protein and reg1 is theregulatory site?i. F′ (reg1−reg2+emu1−emu2+)/reg1+reg2+emu1+emu2−ii. F′ (reg1+reg2−emu1−emu2+)/reg1+reg2+emu1+emu2−c. What results do you predict for the two strains(i and ii) if reg1 encodes the regulatory proteinand reg2 is the regulatory site?
Researchers have successfully used gene therapy toameliorate some human genetic diseases by adding anormal gene copy to cells whose genomes originallyhad only nonfunctional mutant copies of that gene.For example, a form of blindness due to the lack of asingle protein called RPE65 has been reversed byintroduction of a normal RPE65 gene to cells of theretina of adults.a. The success of this gene therapy approach providesus with clues about the role of the RPE65 proteinin the retina. Do you think that RPE65 is neededfor the proper development of the human eye?b. Can you see a potential difficulty in applying this genetherapy approach for diseases like microcephaly?
An investigator was interested in studying UAG nonsense suppressor mutations in bacteria. In one speciesof bacteria, she was able to select two different mutants of this type, one in a tRNATyr gene and the otherin a tRNAGln gene, but in a second species, she wasnot able to obtain any such nonsense suppressor mutations, even after very extensive effort. What couldexplain the difference between the two species?
There is Hyaluronic acid synthesis occuring in Group X Strep and it is controlled by an operon with 3 genes, called hasXYZ. Based on the 3-line diagram model, a. How many ribosome binding sites are there for the protein? b. How many promoters are there for the genes? c. How many start codons are there for the protein? d. How many RNA Polymerase binding locations are there for the genes? e. How many proteins will be fully functional? f. How many mRNA strands are made?
Strain ROFL4 has a premature stop mutation in the lacZ gene, resulting in a nonfunctional b-galactosidase. Otherwise all other parts of the operon are functional. Circle the least number of components for an F' plasmid that will restore normal regulation and function of the lac operon in the resulting partial diploid. (may need more than one) (a) lacI+ (b) lacO+ (c) lacP+ (d) lacZ+ (e) None, cannot be restored.
On its chromosome, an E. coli cell has a genotype of lacI− lacZ+ lacY+ lacA+. It has an F′ factor with a genotype of lacI+ lacZ+ lacY+ lacA+. What is the expected level of expression of the lac operon genes (lacZ+ lacY+ lacA+) in the absence of lactose?a. Both lac operons will be expressed.b. Neither lac operon will be expressed.c. Only the chromosomal lac operon will be expressed.d. Only the lac operon on the F′ factor will be expressed.
The figure at the beginning of this chapter showsthe binding of both a Lac repressor tetramer and aCRP-cAMP complex to the regulatory region of thelac operon.a. What is the key feature of a regulatory protein suchas the Lac repressor or CRP that allows it to regulate specifically the genes or operons it is supposedto control?b. On the figure, show the positions of the followingcomponents: (i) A Lac repressor monomer; (ii) a Lacrepressor dimer; (iii) all four DNA binding domains ofthe Lac repressor tetramer; (iv) a single helix-turnhelix motif; (v) the o1 part and either the o2 or o3 partsof the lac operator (assume the operon would be transcribed from right to left on the figure); (vi) themultimerization domains of the four Lac repressormonomers; (vii) an inducer-interacting domain; (viii)the CRP-cAMP complex; and (ix) a DNA loop.c. What is the physical basis for the formation of theDNA loop shown in the figure?d. On the figure, show the position of two axes ofsymmetry in the sequence…
Why is it adaptive for the structural genes for using lactose to be under the control of a single promoter (i.e., synthesize a polycistronic message rather than three monocistronic messages)? a. For efficient absorption and catabolism of lactose, structural genes send a single signal. This is why polycistronic message is favored more than the monocistronic message since the former involves transmission of numerous messages in initiation and termination. b. Polycistronic message is favored more than the monocistronic message. c. Polycistronic message is favored more than the monocistronic message since the former involves transmission of numerous messages in initiation and termination. d. For an efficient absorption and catabolism of lactose, structural genes send a single signal only. e. Polycistronic message is favored more than the monocistronic message since the former involves transmission of single message in initiation and termination.
Suppose you have six strains of E. coli. One is wildtype, and each of the other five has a single one of thefollowing mutations: lacZ−, lacY−, lacI−, oc, andlacIS. For each of these six strains, describe thephenotype you would observe using the following assays. [Notes: (1) IPTG is a colorless synthetic molecule that acts as an inducer of lac operon expressionbut cannot serve as a carbon source for bacterialgrowth because it cannot be cleaved byβ-galactosidase; (2) X-gal cannot serve as a carbonsource for growth; (3) E. coli requires active lactosepermease (the product of lacY) to allow lactose,X-gal, or IPTG into the cells.] Colony color in medium containing glycerol as theonly carbon source and X-gal, but no IPTG.d. Colony color in medium containing high levels ofglucose as the only carbon source, X-gal, andIPTG.e. Colony color in medium containing high levels ofglucose as the only carbon source and X-gal, butno IPTG
. Suppose you have six strains of E. coli. One is wildtype, and each of the other five has a single one of thefollowing mutations: lacZ−, lacY−, lacI−, oc, andlacIS. For each of these six strains, describe thephenotype you would observe using the following assays. [Notes: (1) IPTG is a colorless synthetic molecule that acts as an inducer of lac operon expressionbut cannot serve as a carbon source for bacterialgrowth because it cannot be cleaved byβ-galactosidase; (2) X-gal cannot serve as a carbonsource for growth; (3) E. coli requires active lactosepermease (the product of lacY) to allow lactose,X-gal, or IPTG into the cells.]a. Growth on medium in which the only carbonsource was lactose.b. Colony color in medium containing glycerol as theonly carbon source, X-gal, and IPTG