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ASU Bio 340 Exam 3 2024 Questions and Answers Verified Solutions 2024/2025 Complete 100% Correct
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ASU BIO 340 Exam 3.pdf file:///C:/Users/HP/Desktop/New%20Conver/ASU%20BIO%20340ASU BIO 340 Exam 3
1. What will be the effect on transcription when an inhibitor is in play?
A. Allow transcription B. Prevent transcription
ANS B Explanation
An inhibitor pre- vents activator from binding to DNA; activators are used in positive
regulation (increasing transcription) - thus, the inhibitor prevents the activator from positive
regulating (increasing) transcription.
2. What will be the effect on transcription when an inducer is in play?
A. Allow transcription B. Prevent transcription
ANS A Explanation
When an inducer is in play, it will allow transcription.
3. For a gene under positive control, which of the following would prevent
transcription?
A. Repressor B. Corepressor C. Inducer D. Effector E. Inhibitor
ANS E Explanation Positive regulation includes activators (affected by effectors and inhibitors);
inhibitors prevent activator from binding to DNA, thus preventing transcription.
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4. 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
ANS 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.
5. Which molecule serves as the inducer for the lac operon?
A. cAMP B. Glucose C. Lactose D. Allolactose
ANS D Explanation Allolactose is the molecule that binds to repressor protein, making it unable
to bind to the operator.
6. Which of the following conditions will result in the greatest levels of tran- scription of
the lac operon?
A. Lactose absent, glucose absent B. Lactose absent, glucose present C. Lactose present,
glucose present D. Lactose present, glucose absen
ANS D Ex- planation
From the perspective of the cell, it is most efficient to repress expression of the genes allowing
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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.
7. Which of the following mutations will result in the lowest level of transcrip- tion 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
ANS D Explanation
A - if repressor can't bind, the gene will be permanently turned on,
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