Reading Quiz #19

24 July 2022
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question
Which of the following levels of gene expression control allows a cell to respond most rapidly to a changing environment?
answer
post-translational control
question
At which of the following stages does transcriptional control occur? a b c DNA β€”β€”> mRNA β€”β€”> protein β€”β€”> activated protein
answer
a
question
Imagine that you want to isolate mutant cells that are deficient in the enzymes required to synthesize tryptophan. You decide to use a replica plating protocol similar to Figure 18.3. What should the composition of the growth media in the master and replica plates be?
answer
Master: Complete medium (contains glucose) plus tryptophan Replica: Complete medium minus tryptophan
question
What is the pattern of expression of Ξ²-galactosidase in lacIβ€” cells and why?
answer
Constitutive expression, because there is no repressor
question
The lac repressor protein binds to the operator when it is ______.
answer
not bound to lactose
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The operon model of the regulation of gene expression in bacteria was proposed by _____.
answer
Jacob and Monod
question
Which of these is NOT a component of the lac operon?
answer
regulatory gene only
question
Regulatory proteins bind to _____.
answer
the operator
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In the presence of a regulatory protein the lac operon is _____.
answer
not transcribed
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In this animation the blue sphere represents _____.
answer
lactose
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In this animation the orange object represents _____.
answer
RNA polymerase
question
Which of these is a regulatory gene?
answer
D
question
A(n) _____ is a stretch of DNA consisting of an operator, a promoter, and genes for a related set of proteins, usually making up an entire metabolic pathway.
answer
operon
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The _____ is/are arranged sequentially after the promoter.
answer
genes of an operon
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A(n) _____ is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.
answer
promoter
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A(n) _____ codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes.
answer
regulatory genes
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Regulatory proteins often bind to the _____ to control expression of the operon.
answer
operator
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A(n) _____ is a protein that inhibits gene transcription. In bacteria, this protein binds to the DNA in or near the promoter.
answer
repressor
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A(n) _____ is a specific small molecule that binds to a bacterial repressor protein and changes its shape so that it cannot bind to an operator, thus switching an operon on.
answer
inducer
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operon not transcribed
answer
lactose absent
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operon transcribed at a LOW rate
answer
lactose present, glucose present
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operon transcribed at a HIGH rate
answer
lactose present, glucose absent
question
AraC binds to _____ in the presence of arabinose.
answer
initiator
question
AraC binds to _____ in the absence of arabinose.
answer
initiator and operator
question
AraC binds to _____ if a mutation prevents arabinose from binding to AraC.
answer
initiator and operator
question
AraC binds to _____ if arabinose is present but a mutation in araD enzyme renders it non-functional.
answer
initiator
question
AraC acts as _____ in the presence of arabinose.
answer
activator
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AraC acts as _____ in the absence of arabinose.
answer
repressor
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AraC acts as _____ if a mutation prevents arabinose from binding to AraC.
answer
repressor
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AraC acts as _____ if arabinose is present but a mutation in araD enzyme renders it non-functional.
answer
activator
question
Does transcription of the ara operon occur in the presence of arabinose?
answer
Yes
question
Does transcription of the ara operon occur in the absence of arabinose?
answer
No
question
Does transcription of the ara operon occur if a mutation prevents arabinose from binding to AraC?
answer
No
question
Does transcription of the ara operon occur if arabinose is present but a mutation in araD enzyme renders it non-functional?
answer
Yes
question
Does arabinose metabolism occur in the presence of arabinose?
answer
Yes
question
Does arabinose metabolism occur in the absence of arabinose?
answer
No
question
Does arabinose metabolism occur if a mutation prevents arabinose from binding to AraC?
answer
No
question
Does arabinose metabolism occur if arabinose is present but a mutation in araD enzyme renders it non-functional?
answer
No
question
Regarding regulation of the ara operon, what would be the effect of a mutation that removes the part of the AraC protein that binds to RNA Polymerase?
answer
Transcription would not occur at high levels in either the presence or absence of arabinose.
question
Which aspect of normal lac operon function is an example of post-translational control?
answer
Interaction of lactose with the repressor
question
A type of mutation in the lac operator known as lacOc prevents repressor binding to DNA and causes constitutive transcription of the lac operon. Which of the following secondary mutations might restore normal regulation to the lac operon in a lacOc mutant?
answer
a lacI mutation that produces a repressor than can recognize the mutated lacOc DNA sequence
question
Colonies of what color are produced by cells with functioning copies of Ξ²-galactosidase?
answer
blue
question
Colonies of what color are produced by cells with mutations in the lacZ or in the lacY genes?
answer
white
question
Suppose you analyze the protein-coding sequence of the lacZ and lacY genes of cells from the three mutant colonies and find that these sequences are wild type (normal). What other region of the lac operon might be altered to account for the mutant phenotype of these colonies?
answer
the lac promoter