Concept explainers
To review:
The efficiency of the promoter for the repressor protein and whether the synthesis of the repressor is constitutive or inducible.
Introduction:
The regulatory proteins bind to the DNA (deoxyribonucleic acid) and play a key role in determining which genes are to be activated. These are of two types, namely, the repressor and activator proteins. The proteins, whose synthesis is regulated by inducers are known as inducible proteins, while the proteins that are synthesized at a constant rate all the time are known as constitutive proteins.
In the given case, a regulatory gene codes for the repressor protein, which is synthesized in small quantities at a constant rate. This protein acts on the lac operon of Escherichia coli (E. coli). A promoter is a DNA region, which initiates the process of transcription of a certain gene by binding with the ribonucleic acid (RNA) polymerase.
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EBK LIFE: THE SCIENCE OF BIOLOGY
- How does the repressor protein contribute to selective expression of the structural genes Z, Y, and A in the lac operon? The repressor protein is only expressed when lactose is present. The repressor is always expressed. It blocks transcription when lactose is present. The repressor is always expressed. It allows transcription when lactose is absent. The repressor is always expressed. It blocks transcription when lactose is absent. The repressor protein is only expressed when lactose is absent.arrow_forwardGiven the following mutant and conditions, predict the expression of the lacZ gene (no expression, basal level, activate level of expression). A mutant of E. coli that has a mutation in the operator of the lac operon that prevents the repressor from binding. + glucose, - lactose + glucose, + lactose – glucose, + lactosearrow_forwardThe lac operon is a negative inducible system and allolactose will bind to the regulator protein when present. Which of the following is true? the free repressor (not bound by the inducer) cannot bind to the operator. allolactose must bind to the lac repressor protein, preventing it from binding to DNA, in order for the structural genes to be transcribed. allolactose must be absent in order for the structural genes to be transcribed. the presence of allolactose prevents transcription of the the lacl gene, which encodes the lac repressor.arrow_forward
- A theoretical operon (theo) in E. coli contains several structural genes encoding enzymes that are involved sequentially in the biosynthesis of an amino acid. Unlike the lac operon, in which the repressor gene is separate from the operon, the gene encoding the regulator molecule is contained within the theo operon. When the end product (the amino acid) is present, it combines with the regulator molecule, and this complex binds to the operator, repressing the operon. In the absence of the amino acid, the regulatory molecule fails to bind to the operator, and transcription proceeds. Characterize this operon, then consider the following mutations, as well as the situation in which the wild-type gene is present along with the mutantgene in partially diploid cells (F¿):(a) Mutation in the operator region.(b) Mutation in the promoter region.(c) Mutation in the regulator gene.In each case, will the operon be active or inactive in transcription, assuming that the mutation affects the…arrow_forwardLike the lac operon, the hexose operon is controlled by a separate regulatory protein under the control of its own promoter (see the schematic of the operon below). The hexose regulatory protein is sensitive to fatty acyl CoA levels. When all hexose fuel sources are depleted, the bacteria switch to lipid metabolism and fatty acyl CoA levels increase. This turns expression of the hexose operon off. +1 +1 Regulatory Gene regulator Hexose Operon Genes operon regulator promoter operon promoterarrow_forwardWhich of the following statements about the lactose operon in E. coli is TRUE? It contains the genes that encode the proteins for lactose metabolism. Its transcription is blocked when allolactose binds to the lac repressor. It contains a promoter, an operator and an attenuator. It is barely transcribed, when lactose is present in the medium and glucose is absent. It is transcribed at very high levels, when lactose is absent, and glucose is present.arrow_forward
- What would happen if the operator sequence of the lac operon contained a mutation that prevented the repressor protein from binding the operator? (Explain what would happen both in the presence and absence of lactose)arrow_forwardFor the following types of transcriptional control, indicate whether the protein produced by the regulator gene will be synthesized initially as an active repressor or as an inactive repressor. Q. Negative control in an inducible operonarrow_forwardOne way that regulation is often studied is by examining the effects of mutations. For example, mutations within the parts of the lac operon have been well studied. Which of these mutants would be considered a constitutive mutant (the operon is always on)? a mutation in CAP that prevents the binding of CAMP a mutation in one of the structural genes that prevents the transport of lactose into the cell a mutation that disables the promoter for the operon a mutation that disables the repressorarrow_forward
- You 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_forwardDescribe how the components of the trp operon system are affected by a mutation in trpC? Why is it that once enviornmental tryptophan is inserted into the cell, only the trp repressor is activated (turned on)?arrow_forwardThe fictional bacteria Plumbumbacter aurus converts the lead ions to gold ions and uses the resulting electrons to create ATP. aurus has the midas operon which includes the promoter (midasP), the operator (midasO), and eight genes that encode proteins involved in converting lead to gold. The midas operon is regulated by the protein encoded by the midasR gene and the presence of gold ions. When the concentration of gold ions is low, the midas operon is transcribed and the bacteria convert lead into gold. When the concentration of gold is high, the midas operon is off. To better understand regulation of the midas operon, you created P. aurus mutants. The midasR- mutant has a nonfunctional midasR, the midasO- mutant has a nonfunctional midasO, and the midasP-mutant has a nonfunctional midasP. Based on the data below, the midas operon has what type of transcription control? (negative inducible, negative repressible, positive inducible, positive repressible) Strain Produces Gold in…arrow_forward
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