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 2TYK
Summary Introduction
Introduction:
The gene expression and the changes undergone enable a bacterial cell to positively respond to the changes in the environment. Gene products are produced or activated only when required for an associated biological functioning of product. The gene expression is controlled at three stages, namely, the transcription, translation, and the post-transcription.
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A mutation in the operator region of the trp operon can prevent the trp repressor from binding to this operator. When these mutant cells are placed in a solution containing chicken broth, which of the following happens?
a. Tryptophan would bind to the repressor.
b. The Repressor would bind to the operator irrespective of the presence of amino acids in the environment.
c. The transcription of the trip operon would be inhibited.
d. The transcription of the repressor protein is inhibited
E. coli are grown on a medium containing lactose. Once glucose is added to the medium, the bacteria stop fermenting lactose. Which of the following BEST explains the observed effect?
A. Cellular levels of cAMP are lowB.Glucose is bound to the promoter
C. Repressor protein is bound to the operator
D. Repressor protein is bound to the promoter
You are growing E. coli in a laboratory in order to study their operons. The growth media you are using contains lactose, no glucose and no tryptophan. Using your knowledge of operons and their regulation
a.Which operons would be functional under these conditions?
b.What repressors would be made? (NOTE: name the repressors using their gene names)
c.Which repressor(s) would be made in the inactive form?
d.Which repressor(s) would be made in the active form?
e.Which repressor(s) under these conditions can bind the operator sequence?
f.Which repressor(s)under these conditions cannot bind the operator sequence?
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- How does the lac operon regulate lactose digestion in bacteria?a. The repressor protein becomes a lactose-digesting enzyme onlywhen lactose is present.b. The repressor protein binds to the lac operon when lactose ispresent, blocking transcription.c. When lactose is present, it binds to the operator region of the lacoperon, activating transcription of the repressor protein gene.d. The repressor protein falls off the lac operon when lactose ispresent, and lactose-digesting genes are expressed.arrow_forwardTheara operon is an inducible operon that controls the production of the sugar arabinose. When arabinose is present in a bacterium it binds to the protein AraC, and the complex binds to the initiator site to promote transcription. In this scenario, AraC is a(n) ________. a. activator b. inducer c. repressor d. operatorarrow_forwardE. coli has five genes that code for enzymes that make tryptophan. These genes are regulated by a single promoter and transcribed as one long gene. The presence of tryptophan shut down the production of tryptophan by the cell by binding to the repressor. This changes the repressors shape allowing it to bind to DNA operator, blocking RNA polymerase and cutting off the production of tryptophan. a. Describe what woud happen to the operon if some of the cells had a mutation on the repressor, not allowing it to bind with tryptophan. The repressor is described as an allosteric protein. What does this mean? b. Does the tryptophan model demonstrate an inducible or repressible operon? What is your evidence? *arrow_forward
- E. coli has five genes that code for enzymes that make tryptophan. These genes are regulated by a single promoter and transcribed as one long gene. The presence of tryptophan shut down the production of tryptophan by the cell by binding to the repressor. This changes the repressors shape allowing it to bind to DNA operator, blocking RNA polymerase and cutting off the production of tryptophan. a. Describe what would happen to the operon if some of the cells had a mutation on the repressor, not allowing it to bind with tryptophan. The repressor is described as an allosteric protein. What does this mean? b. Does the tryptophan model demonstrate an inducible or repressible operon? What is your evidence?*arrow_forwardIn the trp operon, tryptophan is best characterized as being a: A. repressor B. inducer C. corepressor D. DNA-binding domainarrow_forwardControl of the trp operon relies on which of the following: a. High levels of tryptophan causing a pause (but not termination) in transcription b. Low levels of tryptophan causing a pause (but not termination) in transcription c. Allolactose binding to the inhibitor to prevent it from binding to the promoter d. Tryptophan binding to the inhibitor to prevent it from binding to the promoterarrow_forward
- Which of the following statements about trp operon regulation is TRUE? A. Low trp levels result in trp repressor binding. O B. High trp levels result in transcriptional antitermination. C. Low trp levels cause the ribosome to fall off at the trp codons in the upstream ORF. O D. High trp levels cause the ribosome to fall off at the trp codons in the upstream ORF. O E. Low trp levels result in transcriptional antitermination. QUESTION 34 Consider the following partial diploid for the lac operon system. lacl+ O+ lac Z+Y-A- lacls O+ 1. 2. lac Z-Y+ A+ In this configuration, which of the following statements is TRUE? A. With no lac present, ZYA will all be expressed. B. with lac present none of the genes (ZYA) will be expressed. O C. With no lac present, only YA will be expressed. D. None of these answers is correct. E. With no lac present, only Z will be expressed.arrow_forwardDefine the following in the context of operons: a. positive control b. give an example of an operon that is under positive control c. negative control d. give an example of an operon that is under negative control e. repressor f. give an example of a repressor molecule g. activator h. give an example of an activatorarrow_forwardWhen iron is scarce, some bacteria can stop synthesis of all enzymes that require iron (Fe3+), such as superoxide dismutase (SOD). Which of the following accurately describes a mechanism for this regulation? Mark all that apply. A. Regulation occurs by an inducible operon B. When absent, the lack of iron causes the repressor to deactivate and block the promoter region for these genes C. Regulation occurs by a repressible operon D. When present, iron binds and activates the repressor proteinarrow_forward
- Mutations may have an effect on the expression of the lac operon and the trp operon. Would the following mutations have a cis- or transeffect on the expression of the protein-encoding genes in the operon? A. A mutation in the operator site that prevents lac repressor from binding to it B. A mutation in the lacI gene that prevents lac repressor from binding to DNA C. A mutation in the trpL gene that prevents attenuationarrow_forwardIn the lac operon, the lac genes are transcribed in the presence of lactose because a RNA polymerase binds to the operator b The repressor can not bind the promoter c Production of the repressor protein is inducible d The inducer binds to the repressor e The inducer binds to the operatorarrow_forwardWhat is the role of a substrate that controls a repressible operon? a. increase the production of inactive repressor proteins b. bind to the repressor protein and activate it c. bind to the repressor protein and deactivate it d. bind to the promoter region and decrease the affinity of RNA polymerase for the promoterarrow_forward
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