ASU BIO 340 Exam 3
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B Explanation: An inhibitor prevents ac-
What will be the effect on transcription tivator from binding to DNA; activators
when an inhibitor is in play? are used in positive regulation (increas-
A. Allow transcription B. Prevent tran- ing transcription) - thus, the inhibitor pre-
scription vents the activator from positive regulat-
ing (increasing) transcription.
What will be the effect on transcription
when an inducer is in play? A Explanation: When an inducer is in
A. Allow transcription B. Prevent tran- play, it will allow transcription.
scription
For a gene under positive control, which E Explanation: Positive regulation in-
of the following would prevent transcrip- cludes activators (affected by effectors
tion? and inhibitors); inhibitors prevent activa-
A. Repressor B. Corepressor C. Inducer tor from binding to DNA, thus preventing
D. Effector E. Inhibitor transcription.
C Explanation: In negative regulation,
there are repressors (affected by corre-
For a gene under negative control, which pressors and inducers). If there were a
of the following would you expect to find corepressor, the repressor would suc-
bound to the repressor if there is active cessfully bind to the operator and prevent
transcription? A. Repressor B. Corepres- transcription. Inducers, however, prevent
sor C. Inducer D. Effector E. Inhibitor the binding of the repressor - thus caus-
ing a prevention of it doing its job, and
allowing transcription.
Which molecule serves as the inducer
D Explanation: Allolactose is the mole-
for the lac operon?
cule that binds to repressor protein, mak-
A. cAMP B. Glucose C. Lactose D. Allo-
ing it unable to bind to the operator.
lactose
D Explanation: From the perspective of
Which of the following conditions will re- the cell, it is most efficient to repress
sult in the greatest levels of transcription expression of the genes allowing for me-
of the lac operon? tabolism of lactose when it's absent, to
A. Lactose absent, glucose absent B. allow it when present, but only to priori-
Lactose absent, glucose present C. Lac- tize it when glucose (the preferred food
tose present, glucose present D. Lactose source) is absent. In C, allolactose will
present, glucose absen also be present, allowing transcription,
but positive regulation (i.e. increase in
1/7
, ASU BIO 340 Exam 3
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transcription) only happens as in D, when
glucose is absent.
Which of the following mutations will re-
D Explanation: A - if repressor can't bind,
sult in the lowest level of transcription of
the gene will be permanently turned on,
the lac operon when lactose is present?
there will be transcription. B - exactly
A. An operator mutation that prevents
the same effect as A. C - "tempting but
binding of the lac repressor B. A mutation
wrong"; CAP can't bind, will cause lower
in the lac repressor that prevents it from
but not total prevention of transcription.
binding to the operator C. A mutation in
D - correct answer; if the inducer is to-
CAP that prevents it from binding to the
tally ineffective, then the repressor will
CAP binding site D. A mutation in the lac
permanently bind to operator and totally
repressor that prevents it from binding
prevent transcription.
allolactose
The regulatory elements in the lac oper-
on act to: E Explanation: The cell wants to both
A. Repress transcription when there is no repress transcription when there is no
lactose present B. Repress transcription lactose present and activate it when glu-
when there is lactose present C. Activate cose is absent (C "slightly less good"
transcription when there is no glucose answer than A, but still true). Similar to
present D. Activate transcription when Clicker Question 6
there is glucose present E. A and C
D Explanation: If you have that lipid, you
would want it to not make any more. So,
A bacterium needs to make a certain
if you have the lipid in the cell, you would
lipid that it cannot obtain from its environ-
want to turn off the transcription, so it
ment. That same lipid is involved in reg-
would likely be involved in negative reg-
ulating the expression of the enzymes
ulation. Effectors and activators are both
that make it. Which of the following is
involved in positive regulation. An induc-
the most likely regulatory function of the
er is under negative regulation but its job
lipid?
is to turn on transcription. A co-repressor
A. Effector B. Activator C. Inducer D.
will only turn the gene off if there is a
Co-repressor E. Operator
signal the cell can sense. Operator is a
piece of DNA.
A bacterium is unable to transport lac-
B Explanation: If you can't transport lac-
tose into the cell to be broken down.
tose, then it means permease isn't work-
Which gene is likely mutated in this bac-
ing. So lacY is likely mutated since that
terium?
is the gene that encodes permease.
A. lacZ B. lacY C. lacI D. lacP E. lacO
2/7
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B Explanation: An inhibitor prevents ac-
What will be the effect on transcription tivator from binding to DNA; activators
when an inhibitor is in play? are used in positive regulation (increas-
A. Allow transcription B. Prevent tran- ing transcription) - thus, the inhibitor pre-
scription vents the activator from positive regulat-
ing (increasing) transcription.
What will be the effect on transcription
when an inducer is in play? A Explanation: When an inducer is in
A. Allow transcription B. Prevent tran- play, it will allow transcription.
scription
For a gene under positive control, which E Explanation: Positive regulation in-
of the following would prevent transcrip- cludes activators (affected by effectors
tion? and inhibitors); inhibitors prevent activa-
A. Repressor B. Corepressor C. Inducer tor from binding to DNA, thus preventing
D. Effector E. Inhibitor transcription.
C Explanation: In negative regulation,
there are repressors (affected by corre-
For a gene under negative control, which pressors and inducers). If there were a
of the following would you expect to find corepressor, the repressor would suc-
bound to the repressor if there is active cessfully bind to the operator and prevent
transcription? A. Repressor B. Corepres- transcription. Inducers, however, prevent
sor C. Inducer D. Effector E. Inhibitor the binding of the repressor - thus caus-
ing a prevention of it doing its job, and
allowing transcription.
Which molecule serves as the inducer
D Explanation: Allolactose is the mole-
for the lac operon?
cule that binds to repressor protein, mak-
A. cAMP B. Glucose C. Lactose D. Allo-
ing it unable to bind to the operator.
lactose
D Explanation: From the perspective of
Which of the following conditions will re- the cell, it is most efficient to repress
sult in the greatest levels of transcription expression of the genes allowing for me-
of the lac operon? tabolism of lactose when it's absent, to
A. Lactose absent, glucose absent B. allow it when present, but only to priori-
Lactose absent, glucose present C. Lac- tize it when glucose (the preferred food
tose present, glucose present D. Lactose source) is absent. In C, allolactose will
present, glucose absen also be present, allowing transcription,
but positive regulation (i.e. increase in
1/7
, ASU BIO 340 Exam 3
Study online at https://quizlet.com/_7fnj4d
transcription) only happens as in D, when
glucose is absent.
Which of the following mutations will re-
D Explanation: A - if repressor can't bind,
sult in the lowest level of transcription of
the gene will be permanently turned on,
the lac operon when lactose is present?
there will be transcription. B - exactly
A. An operator mutation that prevents
the same effect as A. C - "tempting but
binding of the lac repressor B. A mutation
wrong"; CAP can't bind, will cause lower
in the lac repressor that prevents it from
but not total prevention of transcription.
binding to the operator C. A mutation in
D - correct answer; if the inducer is to-
CAP that prevents it from binding to the
tally ineffective, then the repressor will
CAP binding site D. A mutation in the lac
permanently bind to operator and totally
repressor that prevents it from binding
prevent transcription.
allolactose
The regulatory elements in the lac oper-
on act to: E Explanation: The cell wants to both
A. Repress transcription when there is no repress transcription when there is no
lactose present B. Repress transcription lactose present and activate it when glu-
when there is lactose present C. Activate cose is absent (C "slightly less good"
transcription when there is no glucose answer than A, but still true). Similar to
present D. Activate transcription when Clicker Question 6
there is glucose present E. A and C
D Explanation: If you have that lipid, you
would want it to not make any more. So,
A bacterium needs to make a certain
if you have the lipid in the cell, you would
lipid that it cannot obtain from its environ-
want to turn off the transcription, so it
ment. That same lipid is involved in reg-
would likely be involved in negative reg-
ulating the expression of the enzymes
ulation. Effectors and activators are both
that make it. Which of the following is
involved in positive regulation. An induc-
the most likely regulatory function of the
er is under negative regulation but its job
lipid?
is to turn on transcription. A co-repressor
A. Effector B. Activator C. Inducer D.
will only turn the gene off if there is a
Co-repressor E. Operator
signal the cell can sense. Operator is a
piece of DNA.
A bacterium is unable to transport lac-
B Explanation: If you can't transport lac-
tose into the cell to be broken down.
tose, then it means permease isn't work-
Which gene is likely mutated in this bac-
ing. So lacY is likely mutated since that
terium?
is the gene that encodes permease.
A. lacZ B. lacY C. lacI D. lacP E. lacO
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