ASU BIO 340 EXAM 3 FINAL PAPER 2026
COMPLETE QUESTIONS AND CORRECT
ANSWERS GRADED A+
⩥ 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.
⩥ 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.
COMPLETE QUESTIONS AND CORRECT
ANSWERS GRADED A+
⩥ 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.
⩥ 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.
