Concept explainers
To analyze:
For the lac operon partial diploids mentioned in the question, determine whether the synthesis of lac Z mRNA is constitutive, inducible, or uninducible, and indicate whether the partial diploid is
Introduction:
An operon is a stretch of DNA which consists of a cluster of functionally related genes. It contains an operator, promoter, and related genes. It is present only in prokaryotes. It was first characterized in E. coli. Operon can be inducible or repressible.
Inducible operon: In the presence of a substrate, transcription of structural gene occurs, and in
the absence of a substrate, operator region is occupied by the repressor. So, RNA polymerase is unable to bind at the promoter region, and transcription cannot be initiated. In inducible operon
transcription in inhibited in the absence of a substrate.
Repressible operon: In a repressible operon, the substrate acts as a co-repressor which facilitates the conformational change in the repressor of the operon, and transcription is inhibited in the absence of a co-repressor. The conformation of the original repressor does not allow it to bind the operator region of the operon. Thus, the operator region is free, and RNA polymerase can bind at the promoter region, and the transcription of genes can be initiated.
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Genetic Analysis: An Integrated Approach (2nd Edition)
- 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 IPTGarrow_forward. 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 IPTGarrow_forwardGive all possible genotypes of a lac operon that produces, or fails to produce, β-galactosidase and permease under the following conditions. Do not give partial-diploid genotypes. Lactose absent Lactose present β-Galactosidase Permease β-Galactosidase Permease a. − − + + b. − − − + c. − − + − d. + + + + e. − − − − f. + − + − g. − + − +arrow_forward
- For each of the following conditions in the Lac Operon, state whether transcription will occur or not and state why. Include all the major actors including glucose, lactose, cAMP and CAP(CPR). Key + (present) - (absent) 1) Glucose-; Lactose- 2) Glucose+; Lactose- 3) Glucose+; Lactose+ 4) Glucose-; Lactose+arrow_forwardTwo closely linked open reading frames (ORFs) have been identified on the E. coli chromosome and they are predicted to encode genes sugX sugY which is involved in the catabolism (utilization) of a non-glucose sugar. In the figure below, the top line (with the big arrow) is the coding strand, and the bottom line is the non-coding (template) strand of the operon. Since the RNA sequence would be the “same” as the coding strand, please label (show the location of), in relation to the ORFs, the promoter(s) and 4 other genetic elements in this region that may be involved in the transcription and translation of sugX and sugY as well as the regulation of their expression. (Note: genetic elements are the regions of DNA or RNA.) If you are not comfortable with the coding strand of the DNA, feel free to draw the mRNA strand underneath and label the relevant features on the RNA strand, but the RNA strand must be aligned with the DNA strands in position and scale. Leader(s)/antileader(s) and…arrow_forwardWhat conservation laws (P- or S- invariants) can be found in the lac operon regulatory Petri net?arrow_forward
- The lac operon consists of regulatory regions such as the promoter as well as the structural genes lacZ, lacY, and lacA, which code for proteins involved in lactose metabolism. What would be the outcome of a mutation in lacA?arrow_forwardWhat experimental results would indicate that the mutation lacISlacIS is dominant to lacI+lacI+? In lacISlacIS/lacI+lacI+ partial diploids, the lac operon is in a repressed state in the absence of lactose. In lacISlacIS/lacI+lacI+ partial diploids, the lac operon is in a constitutive state in the absence of the repressor. In lacISlacIS/lacI+lacI+ partial diploids, the lac operon is in an activated state in the presence of lactose. In lacISlacIS/lacI+lacI+ partial diploids, the lac operon is in a repressed state in the absence of the repressor. In lacISlacIS/lacI+lacI+ partial diploids, the lac operon is in a repressed state in the presence of lactose.arrow_forwardYou have isolated two different mutants (reg1 and reg2) causing constitutive expression of the emu operon (emu1 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. Is the DNA-binding protein a positive or negative regulator of gene expression? Explain. To determine which mutant has a defect in the site and 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 Emu1 and Emu2 proteins, what results do you predict for the two strains (i and ii; see descriptions below) if reg2 encodes the regulatory protein and reg1 is the regulatory site? Explain. F′ (reg1− reg2+ emu1− emu2+)/reg1+ reg2+ emu1+ emu2− F′ (reg1+ reg2− emu1− emu2+)/reg1+ reg2+ emu1+ emu2−arrow_forward
- What is lac operon? Draw and/or identify the status of the lac operon in a given set of environmental conditions and/or cell mutations.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_forwardIn the galactose operon of E. coli, a repressor, encoded by the galR gene, binds to an operator site,galo, to regulate the expression of three structuralgenes, galE, galT, and galK. Expression is inducedby the presence of galactose in the media. For eachof the strains listed, would the cell show constitutive, inducible, or no expression of each of the structural genes? (Assume that galR− is a loss-of-functionmutation.)a. galR−galo+galE+galT+galK+b. galR+galocgalE+galT+galK+ c. galR−galo+galE+galT+galK−/galR+galo+galE−galT+galK+d. galR−galocgalE+galT+galK−/galR+galo+galE−galT+galK+arrow_forward
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