ASU BIO 340 Exam 3 Exam (updated 2026) Questions & Answers | Latest
Already Graded A+ UPDATE |2026
What will be the effect on transcription when an inhibitor is in play?
A. Allow transcription B. Prevent transcription - (ANSWER)B Explanation: An inhibitor prevents activator
from binding to DNA; activators are used in positive regulation (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 - (ANSWER)A Explanation: 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 - (ANSWER)E Explanation: Positive
regulation includes activators (affected by effectors and inhibitors); inhibitors prevent 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
repressor if there is active transcription? A. Repressor B. Corepressor C. Inducer D. Effector E. Inhibitor -
(ANSWER)C Explanation: In negative regulation, there are repressors (affected by correpressors and
inducers). If there 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 - (ANSWER)D Explanation: Allolactose is the molecule that
binds to repressor protein, making it unable to bind to the operator.
Which of the following conditions will result in 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 - (ANSWER)D Explanation: From the perspective of the cell, it is most
efficient to repress expression of the genes allowing for metabolism of lactose when it's absent, to allow
it when present, but only to prioritize it when glucose (the preferred food source) is absent. In C,
allolactose will also be present, allowing transcription, but positive regulation (i.e. increase in
transcription) only happens as in D, when glucose is absent.
, ASU BIO 340 Exam 3 Exam (updated 2026) Questions & Answers | Latest
Already Graded A+ UPDATE |2026
Which of the following mutations will result in the lowest level of transcription of the lac operon when
lactose is present?
A. An operator mutation that prevents binding of the lac repressor B. A mutation in the lac repressor
that prevents it from binding to the operator C. A mutation in CAP that prevents it from binding to the
CAP binding site D. A mutation in the lac repressor that prevents it from binding allolactose -
(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 operator and totally prevent transcription.
The regulatory elements in the lac operon 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
is glucose present E. A and C - (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 Question 6
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
likely regulatory function of the lipid?
A. Effector B. Activator C. Inducer D. Co-repressor E. Operator - (ANSWER)D Explanation: If you have
that lipid, you would want it to not make any more. So, if you have the lipid in the cell, you would want
to turn off the transcription, so it would likely be involved in negative regulation. Effectors and
activators are both involved in positive regulation. An inducer is under negative regulation but its job 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?
A. lacZ B. lacY C. lacI D. lacP E. lacO - (ANSWER)B Explanation: If you can't transport lactose, then it
means permease isn't working. So lacY is likely mutated since that is the gene that encodes permease.
Already Graded A+ UPDATE |2026
What will be the effect on transcription when an inhibitor is in play?
A. Allow transcription B. Prevent transcription - (ANSWER)B Explanation: An inhibitor prevents activator
from binding to DNA; activators are used in positive regulation (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 - (ANSWER)A Explanation: 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 - (ANSWER)E Explanation: Positive
regulation includes activators (affected by effectors and inhibitors); inhibitors prevent 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
repressor if there is active transcription? A. Repressor B. Corepressor C. Inducer D. Effector E. Inhibitor -
(ANSWER)C Explanation: In negative regulation, there are repressors (affected by correpressors and
inducers). If there 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 - (ANSWER)D Explanation: Allolactose is the molecule that
binds to repressor protein, making it unable to bind to the operator.
Which of the following conditions will result in 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 - (ANSWER)D Explanation: From the perspective of the cell, it is most
efficient to repress expression of the genes allowing for metabolism of lactose when it's absent, to allow
it when present, but only to prioritize it when glucose (the preferred food source) is absent. In C,
allolactose will also be present, allowing transcription, but positive regulation (i.e. increase in
transcription) only happens as in D, when glucose is absent.
, ASU BIO 340 Exam 3 Exam (updated 2026) Questions & Answers | Latest
Already Graded A+ UPDATE |2026
Which of the following mutations will result in the lowest level of transcription of the lac operon when
lactose is present?
A. An operator mutation that prevents binding of the lac repressor B. A mutation in the lac repressor
that prevents it from binding to the operator C. A mutation in CAP that prevents it from binding to the
CAP binding site D. A mutation in the lac repressor that prevents it from binding allolactose -
(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 operator and totally prevent transcription.
The regulatory elements in the lac operon 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
is glucose present E. A and C - (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 Question 6
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
likely regulatory function of the lipid?
A. Effector B. Activator C. Inducer D. Co-repressor E. Operator - (ANSWER)D Explanation: If you have
that lipid, you would want it to not make any more. So, if you have the lipid in the cell, you would want
to turn off the transcription, so it would likely be involved in negative regulation. Effectors and
activators are both involved in positive regulation. An inducer is under negative regulation but its job 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?
A. lacZ B. lacY C. lacI D. lacP E. lacO - (ANSWER)B Explanation: If you can't transport lactose, then it
means permease isn't working. So lacY is likely mutated since that is the gene that encodes permease.
