Reading Quiz #19

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Chandler Biology 1330

Which of the following levels of gene expression control allows a cell to respond most rapidly to a changing environment?

post-translational control

At which of the following stages does transcriptional control occur?

a b c
DNA ——> mRNA ——> protein ——> activated protein

a

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?

Master: Complete medium (contains glucose) plus tryptophan Replica: Complete medium minus tryptophan

What is the pattern of expression of β-galactosidase in lacI— cells and why?

Constitutive expression, because there is no repressor

The lac repressor protein binds to the operator when it is ______.

not bound to lactose

The operon model of the regulation of gene expression in bacteria was proposed by _____.

Jacob and Monod

Which of these is NOT a component of the lac operon?

regulatory gene only

Regulatory proteins bind to _____.

the operator

In the presence of a regulatory protein the lac operon is _____.

not transcribed

In this animation the blue sphere represents _____.

lactose

In this animation the orange object represents _____.

RNA polymerase

Which of these is a regulatory gene?

D

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.

operon

The _____ is/are arranged sequentially after the promoter.

genes of an operon

A(n) _____ is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.

promoter

A(n) _____ codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes.

regulatory genes

Regulatory proteins often bind to the _____ to control expression of the operon.

operator

A(n) _____ is a protein that inhibits gene transcription. In bacteria, this protein binds to the DNA in or near the promoter.

repressor

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.

inducer

operon not transcribed

lactose absent

operon transcribed at a LOW rate

lactose present, glucose present

operon transcribed at a HIGH rate

lactose present, glucose absent

AraC binds to _____ in the presence of arabinose.

initiator

AraC binds to _____ in the absence of arabinose.

initiator and operator

AraC binds to _____ if a mutation prevents arabinose from binding to AraC.

initiator and operator

AraC binds to _____ if arabinose is present but a mutation in araD enzyme renders it non-functional.

initiator

AraC acts as _____ in the presence of arabinose.

activator

AraC acts as _____ in the absence of arabinose.

repressor

AraC acts as _____ if a mutation prevents arabinose from binding to AraC.

repressor

AraC acts as _____ if arabinose is present but a mutation in araD enzyme renders it non-functional.

activator

Does transcription of the ara operon occur in the presence of arabinose?

Yes

Does transcription of the ara operon occur in the absence of arabinose?

No

Does transcription of the ara operon occur if a mutation prevents arabinose from binding to AraC?

No

Does transcription of the ara operon occur if arabinose is present but a mutation in araD enzyme renders it non-functional?

Yes

Does arabinose metabolism occur in the presence of arabinose?

Yes

Does arabinose metabolism occur in the absence of arabinose?

No

Does arabinose metabolism occur if a mutation prevents arabinose from binding to AraC?

No

Does arabinose metabolism occur if arabinose is present but a mutation in araD enzyme renders it non-functional?

No

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?

Transcription would not occur at high levels in either the presence or absence of arabinose.

Which aspect of normal lac operon function is an example of post-translational control?

Interaction of lactose with the repressor

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?

a lacI mutation that produces a repressor than can recognize the mutated lacOc DNA sequence

Colonies of what color are produced by cells with functioning copies of β-galactosidase?

blue

Colonies of what color are produced by cells with mutations in the lacZ or in the lacY genes?

white

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?

the lac promoter

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