The lac operon in E. coli is a coordinately controlled set of genes required for lactose metabolism. The operon and its associated regulatory sequences are shown in the following diagram.Two parallel horizontal lines are shown with a break between the first segment and the second segment. The first segment has a box labeled promoter and a box labeled lacI followed by an unlabeled black box. The second segment begins with an unlabeled black box, followed by a box labeled CAP site, a box labeled promoter, a box labeled operator and then 3 boxes with a bracket above them with the caption structural genes. The 3 boxes are labeled lacZ, lacY and lacA.The function of each locus shown in the diagram is listed in the table below.Part FunctionPromoter Binding site for RNA polymeraselacI Gene encoding the lac repressor proteinCAP site Binding site for the catabolite activator proteinOperator Binding site for the lac repressor proteinlacZ Gene encoding the beta-galactosidase proteinlacY Gene encoding the lactose permease proteinlacA Gene encoding the galactoside transacetylase proteinThe activity of the lac operon is influenced by the availability of lactose and glucose in the cellular environment. In the presence of lactose, the lac repressor protein is released from the operator, which allows the structural genes to be transcribed at a low level. If glucose (the preferred carbon source) is absent during this time, the catabolite activator protein binds to the CAP site, causing the structural genes to be transcribed at a higher level.Which of the following is the most likely result of a mutation in the lac repressor protein that prevents binding to the operator?Choose 1 answer:Choose 1 answer:(Choice A, Checked) The catabolite activator protein will not bind to the CAP site, even in the absence of glucose.AThe catabolite activator protein will not bind to the CAP site, even in the absence of glucose.(Choice B) The lacI gene will be highly expressed, even in the presence of glucose.BThe lacI gene will be highly expressed, even in the presence of glucose.(Choice C) The structural genes will not be transcribed, even in the presence of lactose.CThe structural genes will not be transcribed, even in the presence of lactose.(Choice D) The lactose permease protein will be produced, even in the absence of lactose.DThe lactose permease protein will be produced, even in the absence of lactose.
Question
The lac operon in E. coli is a coordinately controlled set of genes required for lactose metabolism. The operon and its associated regulatory sequences are shown in the following diagram.Two parallel horizontal lines are shown with a break between the first segment and the second segment. The first segment has a box labeled promoter and a box labeled lacI followed by an unlabeled black box. The second segment begins with an unlabeled black box, followed by a box labeled CAP site, a box labeled promoter, a box labeled operator and then 3 boxes with a bracket above them with the caption structural genes. The 3 boxes are labeled lacZ, lacY and lacA.The function of each locus shown in the diagram is listed in the table below.Part FunctionPromoter Binding site for RNA polymeraselacI Gene encoding the lac repressor proteinCAP site Binding site for the catabolite activator proteinOperator Binding site for the lac repressor proteinlacZ Gene encoding the beta-galactosidase proteinlacY Gene encoding the lactose permease proteinlacA Gene encoding the galactoside transacetylase proteinThe activity of the lac operon is influenced by the availability of lactose and glucose in the cellular environment. In the presence of lactose, the lac repressor protein is released from the operator, which allows the structural genes to be transcribed at a low level. If glucose (the preferred carbon source) is absent during this time, the catabolite activator protein binds to the CAP site, causing the structural genes to be transcribed at a higher level.Which of the following is the most likely result of a mutation in the lac repressor protein that prevents binding to the operator?Choose 1 answer:Choose 1 answer:(Choice A, Checked) The catabolite activator protein will not bind to the CAP site, even in the absence of glucose.AThe catabolite activator protein will not bind to the CAP site, even in the absence of glucose.(Choice B) The lacI gene will be highly expressed, even in the presence of glucose.BThe lacI gene will be highly expressed, even in the presence of glucose.(Choice C) The structural genes will not be transcribed, even in the presence of lactose.CThe structural genes will not be transcribed, even in the presence of lactose.(Choice D) The lactose permease protein will be produced, even in the absence of lactose.DThe lactose permease protein will be produced, even in the absence of lactose.
Solution
The most likely result of a mutation in the lac repressor protein that prevents binding to the operator would be (Choice D) The lactose permease protein will be produced, even in the absence of lactose.
Here's why:
The lac repressor protein, when functioning normally, binds to the operator and prevents the transcription of the structural genes (lacZ, lacY, and lacA). These genes are responsible for the production of proteins involved in lactose metabolism, including the lactose permease protein.
If a mutation occurs in the lac repressor protein that prevents it from binding to the operator, it would no longer be able to inhibit the transcription of the structural genes. This means that the genes would be transcribed and the corresponding proteins, including the lactose permease protein, would be produced regardless of whether lactose is present or not.
This would not affect the binding of the catabolite activator protein to the CAP site (Choice A) or the expression of the lacI gene (Choice B). It would also not prevent the transcription of the structural genes (Choice C), but rather, it would allow their transcription to occur even in the absence of lactose.
Similar Questions
The lac operon system, first described by Jacob and Monod, regulates lactose metabolism in . The is composed of a gene encoding a protein that normally keeps this operon in the position. Within the , the repressor binds to the , blocking transcription of structural genes needed for lactose metabolism. When is added to a cell's environment, it binds the repressor freeing the operator segment of the DNA. is now able to bind to the promoter, transcribing all three structural genes needed for lactose catabolism. When lactose again becomes depleted in the cell, the repressor binds to the operator blocking additional synthesis of enzymes from the .
Lactose or its analogues act as positive regulators of Lac operon by:Select one:a. Attaching to I gene and preventing its expressionb. Binding to repressor subunits so that the repressor cannot attached to operator locus.c. Increasing the synthesis of catabolic gene activator protein.d. Attaching to promoter region and facilitating the biding of RNA polymerase
In E. coli, transcription of the lac operon would be increased by:Group of answer choicesA missense mutation that disrupts the activity of the catabolite activator protein (CAP).A mutation in the lacI repressor gene that increases the affinity of the repressor for allolactose.A mutation in the lacI repressor gene that increases the affinity of the repressor for the lac operator.The presence of glucose in the growth medium.
If E. coli bacteria are grown in the absence of lactoseMultiple Choicethe repressor will not bind the operator, thus allowing transcription of the lac operon genes.the repressor will bind the operator, thus allowing transcription of the lac operon genes.the repressor will not bind the operator, thus preventing transcription of the lac operon genes.the repressor will bind the operator, thus preventing transcription of the lac operon genes.No answer is correct.
The inducer of the lac operon is lactose.
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