ASU BIO 340 Exam 3 Newest Exam Preparation Newest
2026-2027 With Complete Questions And Correct Detailed
Answers | Brand New Version
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 absent - 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.
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
2026-2027 With Complete Questions And Correct Detailed
Answers | Brand New Version
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 absent - 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.
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
