ASU BIO 340 EXAM 3 QUESTIONS WITH
CORRECT ANSWERS GRADED TO A+
What will be the effect on transcription when an inhibitor is in play?
A. Allow transcription B. Prevent transcription - correct answer-
B Explanation: An inhibitor prevents activator from binding to DNA; activators are used in positive regul
ation (increasing transcription) -
thus, the inhibitor prevents the activator from positive regulating (increasing) transcription.
What will be the effect on transcription when an inducer is in play?
A. Allow transcription B. Prevent transcription - correct answer-
ABExplanation: When an inducer is in play, it will allow transcription.
For a gene under positive control, which of the following would prevent transcription?
A. Repressor B. Corepressor C. Inducer D. Effector E. Inhibitor - correct answer-
E Explanation: Positive regulation includes activators (affected by effectors and inhibitors); inhibitors pre
vent activator from binding to DNA, thus preventing transcription.
For a gene under negative control, which of the following would you expect to find bound to the repress
or if there is active transcription? A. Repressor B. Corepressor C. Inducer D. Effector E. Inhibitor -
correct answer-
C Explanation: In negative regulation, there are repressors (affected by correpressors and inducers). If th
ere were a corepressor, the repressor would successfully bind to the operator and prevent transcription.
Inducers, however, prevent the binding of the repressor -
thus causing a prevention of it doing its job, and allowing transcription.
Which molecule serves as the inducer for the lac operon?
A. cAMP B. Glucose C. Lactose D. Allolactose - correct answer-
D Explanation: Allolactose is the molecule that binds to repressor protein, making it unable to bind to th
e operator.
Which of the following conditions will resultBin the greatest levels of transcription of the lac operon?
A. Lactose absent, glucose absent B. Lactose absent, glucose present C. Lactose present, glucose present
D. Lactose present, glucose absen - correct answer-
D Explanation: From the perspective of the cell, it is most efficient to repress expression of the genes all
, owing for metabolism of lactose when it's absent, to allow it when present, but only to prioritize it whe
n glucose (the preferred food source) is absent. In C, allolactose will also be present, allowing transcripti
on, but positive regulation (i.e. increase in transcription) only happens as in D, when glucose is absent.
Which of the following mutations will result in the lowest level of transcription of the lac operon when l
actose is present?
A. An operator mutation that prevents binding of the lac repressor B. A mutation in the lacBrepressor th
at prevents it from binding to the operator C. A mutation in CAP that prevents it from binding to the CA
P binding site D. A mutation in the lac repressor that prevents it from binding allolactose -
correct answer-D Explanation: A -
if repressor can't bind, the gene will be permanently turned on, there will be transcription. B -
exactly the same effect as A. C -
"tempting but wrong"; CAP can't bind, will cause lower but not total prevention of transcription. D -
correct answer; if the inducer is totally ineffective, then the repressor will permanently bind to operato
r and totally prevent transcription.
The regulatory elements in the lacBoperon act to:
A. Repress transcription when there is no lactose present B. Repress transcription when there is lactose
present C. Activate transcription when there is no glucose present D. Activate transcription when there i
s glucose present E. A and C - correct answer-
E Explanation: The cell wants to both repress transcription when there is no lactose present and activate
it when glucose is absent (C "slightly less good" answer than A, but still true). Similar to Clicker Questio
n6
A bacterium needs to make a certain lipid that it cannot obtain from its environment. That same lipid is
involved in regulating the expression of the enzymes that make it. Which of the following is the most lik
ely regulatory function of the lipid?
A. Effector B. Activator C. Inducer D. Co-repressor E. Operator - correct answer-
D Explanation: If you have that lipid, you would want it to not make any more. So, if you have the lipid i
n the cell, you would want to turn off the transcription, so it would likely be involved in negative regulati
on. Effectors and activators are both involved in positive regulation. An inducer is under negative regulat
ion but itsBjob is to turn on transcription. A co-
repressor will only turn the gene off if there is a signal the cell can sense. Operator is a piece of DNA.
A bacterium is unable to transport lactose into the cell to be broken down. Which gene is likely mutated
in this bacterium?
CORRECT ANSWERS GRADED TO A+
What will be the effect on transcription when an inhibitor is in play?
A. Allow transcription B. Prevent transcription - correct answer-
B Explanation: An inhibitor prevents activator from binding to DNA; activators are used in positive regul
ation (increasing transcription) -
thus, the inhibitor prevents the activator from positive regulating (increasing) transcription.
What will be the effect on transcription when an inducer is in play?
A. Allow transcription B. Prevent transcription - correct answer-
ABExplanation: When an inducer is in play, it will allow transcription.
For a gene under positive control, which of the following would prevent transcription?
A. Repressor B. Corepressor C. Inducer D. Effector E. Inhibitor - correct answer-
E Explanation: Positive regulation includes activators (affected by effectors and inhibitors); inhibitors pre
vent activator from binding to DNA, thus preventing transcription.
For a gene under negative control, which of the following would you expect to find bound to the repress
or if there is active transcription? A. Repressor B. Corepressor C. Inducer D. Effector E. Inhibitor -
correct answer-
C Explanation: In negative regulation, there are repressors (affected by correpressors and inducers). If th
ere were a corepressor, the repressor would successfully bind to the operator and prevent transcription.
Inducers, however, prevent the binding of the repressor -
thus causing a prevention of it doing its job, and allowing transcription.
Which molecule serves as the inducer for the lac operon?
A. cAMP B. Glucose C. Lactose D. Allolactose - correct answer-
D Explanation: Allolactose is the molecule that binds to repressor protein, making it unable to bind to th
e operator.
Which of the following conditions will resultBin the greatest levels of transcription of the lac operon?
A. Lactose absent, glucose absent B. Lactose absent, glucose present C. Lactose present, glucose present
D. Lactose present, glucose absen - correct answer-
D Explanation: From the perspective of the cell, it is most efficient to repress expression of the genes all
, owing for metabolism of lactose when it's absent, to allow it when present, but only to prioritize it whe
n glucose (the preferred food source) is absent. In C, allolactose will also be present, allowing transcripti
on, but positive regulation (i.e. increase in transcription) only happens as in D, when glucose is absent.
Which of the following mutations will result in the lowest level of transcription of the lac operon when l
actose is present?
A. An operator mutation that prevents binding of the lac repressor B. A mutation in the lacBrepressor th
at prevents it from binding to the operator C. A mutation in CAP that prevents it from binding to the CA
P binding site D. A mutation in the lac repressor that prevents it from binding allolactose -
correct answer-D Explanation: A -
if repressor can't bind, the gene will be permanently turned on, there will be transcription. B -
exactly the same effect as A. C -
"tempting but wrong"; CAP can't bind, will cause lower but not total prevention of transcription. D -
correct answer; if the inducer is totally ineffective, then the repressor will permanently bind to operato
r and totally prevent transcription.
The regulatory elements in the lacBoperon act to:
A. Repress transcription when there is no lactose present B. Repress transcription when there is lactose
present C. Activate transcription when there is no glucose present D. Activate transcription when there i
s glucose present E. A and C - correct answer-
E Explanation: The cell wants to both repress transcription when there is no lactose present and activate
it when glucose is absent (C "slightly less good" answer than A, but still true). Similar to Clicker Questio
n6
A bacterium needs to make a certain lipid that it cannot obtain from its environment. That same lipid is
involved in regulating the expression of the enzymes that make it. Which of the following is the most lik
ely regulatory function of the lipid?
A. Effector B. Activator C. Inducer D. Co-repressor E. Operator - correct answer-
D Explanation: If you have that lipid, you would want it to not make any more. So, if you have the lipid i
n the cell, you would want to turn off the transcription, so it would likely be involved in negative regulati
on. Effectors and activators are both involved in positive regulation. An inducer is under negative regulat
ion but itsBjob is to turn on transcription. A co-
repressor will only turn the gene off if there is a signal the cell can sense. Operator is a piece of DNA.
A bacterium is unable to transport lactose into the cell to be broken down. Which gene is likely mutated
in this bacterium?
