Biological Science (7th Edition)
7th Edition
ISBN: 9780134678320
Author: Scott Freeman, Kim Quillin, Lizabeth Allison, Michael Black, Greg Podgorski, Emily Taylor, Jeff Carmichael
Publisher: PEARSON
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Chapter 18, Problem 12PIAT
Summary Introduction
To review:
Whether the genes are transcribed when LuxR is bound or not bound to the DNA (deoxyribonucleic acid) regulatory sequence.
Introduction:
The light-producing genes are organized and operate under positive control. In molecular biology, positive regulation implies that a transcription factor is required to bind at the promoter site in gene to enhance RNA polymerase to initiate transcription. The activator that functions in this operon is LuxR. This activator is responsible for the emission of the light. The light-producing genes of V. fischeri are organized in an operon that is under positive control by an activator protein called LuxR.
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The streptolysin S toxin made by S. pyogenes is encoded by a 9-gene
operon, sagABCDEFGHI. Thinking about what a 3-line diagram would look like for this
operon, answer the following questions. Write numeric answers only. For example, if your
answer is 6 promoters, write only 6.
1) How many promoters control the expression of these genes?
2) How many locations does RNA Polymerase bind to get full expression of these genes?
3) How many ribosome binding sites are needed for full protein expression?
4) How many start codons will be needed for full protein expression?
5) How many mRNA strands will be produced with full operon expression?
6) How many proteins will be produced with full protein expression?
1
Bob determines that Red/pink protein is synthesized at much higher amounts than the Brown protein; Bob thinks that this is how the burger always is perfectly medium-rare (pink/red in the interior of the patty, with a small amount of brown at the burger’s surface). Bob also knows that R and B both are transcribed from the single operon. Briefly describe the biological mechanism allowing for accumulation of more R than B protein.
What would happen if the operator sequence of the trp operon contained a mutation that prevented the repressor protein from binding to the operator? (Explain what would happen in both the presence and absence of tryptophan)
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- 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_forwardA 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_forwardGiven the Table below concerning the lac operon, match the letter with what would be occurring for each scenario. Repressor is bound to the operator, cAMP complex is bound and transcription is prevented. Allolactose is bound to the repressor, cAMP complex is bound, and transcription is prevalent. Allolactose is bound to the repressor, cAMP complex is not assembled, and transcription is slow Repressor is bound to the operator, cAMP complex is not assembled, and transcription is prevented.arrow_forward
- The lac operon consists of three structural genes, lacZ, lacY and lacA that are transcribed as a single polycistronic mRNA. You are given a new strain of Escherichia coli with the following lac operon genotype: p+0°Z•Y*A +// P*O*Z*Y+ A- (i) Explain how the lac I gene affects gene expression. (ii) Explain the function of the lacP in the bacterial operon. (iii) Which part of the lac operon is cis-dominant? Explain.arrow_forwardWhat would happen to the regulation of the tryptophan operon in bacterial cells that express a mutant form of the tryptophan repressor that (1) cannot bind to DNA, (2) cannot bind tryptophan, or (3) binds to DNA even in the absence of tryptophan?arrow_forwardThe lactose operon in E. coli comprises two structural genes and three regulatory components.a.State the name of each structural gene and describe its function: b.) State the name of each regulatory component and describe its functionarrow_forward
- You can determine the regulation of an unknown operon based on descriptions like those in the table below. For each row, choose whether the fact would suggest positive or negative or inducible or repressible regulation and indicate your answer with an X in the column. Only one X should appear in each row. In the presence of the signal, the structural genes are expressed. In the presence of the signal, the structural genes are not expressed. In the absence of the signal, the structural genes are expressed. In the absence of the signal, the structural genes are not expressed. The binding of the regulatory protein to the operon results in structural gene expression. The binding of the regulatory protein to the operon prevents structural gene expression. A mutation in the regulatory protein results in constitutive expression of the structural genes. A mutation in the regulatory protein results in no or low expression of the structural genes. Positive? Negative? Inducible? Repressible?arrow_forwardA haploid E. coli cell has the genotype I ¯ P+ O+ Z+ Y ¯ where the I ¯ indicates that the repressor protein cannot bind to the operator due to a mutation. Which of the following statements about cells with this lac operon genotype are correct? I ¯ P+ O+ Z+ Y ¯ Select all that apply. β-galactosidase will be transcribed constitutively. The cells are able to import lactose across the cell membrane. The cells are lac+ and are able to grow on a medium with lactose but no glucose. RNA polymerase can bind to the promoter.arrow_forwardThe lac operon consists of three structural genes, lacZ, lacY and lacA that are transcribed as a single polycistronic mRNA. The new lac strain of Escherichia coli are as shown below: P+O+Z+Y+A+// P+O+Z+Y+A¯ (i) Illustrate how lactose induces the gene expression in lac 1 $// I-. (ii) Explain the function of the lacP and laco in the bacterial operon.arrow_forward
- In the regulation of the tryophan operon in bacteria, the co-occurence of transcription and translation plays a key role regulating full activation of operon expression. Diagram and explain how during the conditions of high tryptophan concentration this system regulates the expression of genes in 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_forwardSupply the words “off" or “on" in the blanks below: In an inducible operon, transcription is normally and must be turned In a repressible operon, transcription is normally and must be turned Briefly describe the overall function of the structural genes in the lac operon. Briefly describe the overall function of the structural genes in the trp operon. For the following descriptions of the bacterial lac operon, determine if lactose is present (P) or absent (A). The repressor is bound to the operator. The repressor is inactive. RNA polymerase transcribes the structural genes. Allolactose is bound to the repressor For the following descriptions of the bacterial trp operon, determine if tryptophan levels are high (H) or low (L). The repressor is bound to the operator. The repressor is inactive. RNA polymerase transcribes the structural genes. Tryptophan is bound to the repressor.arrow_forward
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