ASU BIO 340 Exam 3 – Questions with Correct Answers 2026 | A+ Study Pack

ASU BIO 340 EXAM 3 QUESTIONS WITH gh gh gh gh gh gh




CORRECT ANSWERS GRADED TO A+
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What will be the effect on transcription when an inhibitor is in play?
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A. Allow transcription B. Prevent transcription - correct answer-
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B Explanation: An inhibitor prevents activator from binding to DNA; activators are used in positive regul
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ation (increasing transcription) -
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thus, the inhibitor prevents the activator from positive regulating (increasing) transcription.
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What will be the effect on transcription when an inducer is in play?
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A. Allow transcription B. Prevent transcription - correct answer-
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ABExplanation: When an inducer is in play, it will allow transcription.
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For a gene under positive control, which of the following would prevent transcription?
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A. Repressor B. Corepressor C. Inducer D. Effector E. Inhibitor - correct answer-
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E Explanation: Positive regulation includes activators (affected by effectors and inhibitors); inhibitors pre
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vent activator from binding to DNA, thus preventing transcription.
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For a gene under negative control, which of the following would you expect to find bound to the repress
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or if there is active transcription? A. Repressor B. Corepressor C. Inducer D. Effector E. Inhibitor -
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C Explanation: In negative regulation, there are repressors (affected by correpressors and inducers). If th
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ere were a corepressor, the repressor would successfully bind to the operator and prevent transcription.
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Inducers, however, prevent the binding of the repressor -
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thus causing a prevention of it doing its job, and allowing transcription.
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Which molecule serves as the inducer for the lac operon?
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A. cAMP B. Glucose C. Lactose D. Allolactose - correct answer-
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D Explanation: Allolactose is the molecule that binds to repressor protein, making it unable to bind to th
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e operator.
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Which of the following conditions will resultBin the greatest levels of transcription of the lac operon?
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A. Lactose absent, glucose absent B. Lactose absent, glucose present C. Lactose present, glucose present
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D. Lactose present, glucose absen - correct answer-
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D Explanation: From the perspective of the cell, it is most efficient to repress expression of the genes all
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, owing for metabolism of lactose when it's absent, to allow it when present, but only to prioritize it whe
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n glucose (the preferred food source) is absent. In C, allolactose will also be present, allowing transcripti
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on, but positive regulation (i.e. increase in transcription) only happens as in D, when glucose is absent.
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Which of the following mutations will result in the lowest level of transcription of the lac operon when l
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actose is present?
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A. An operator mutation that prevents binding of the lac repressor B. A mutation in the lacBrepressor th
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at prevents it from binding to the operator C. A mutation in CAP that prevents it from binding to the CA
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P binding site D. A mutation in the lac repressor that prevents it from binding allolactose -
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correct answer-D Explanation: A - gh gh gh gh




if repressor can't bind, the gene will be permanently turned on, there will be transcription. B -
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exactly the same effect as A. C -
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"tempting but wrong"; CAP can't bind, will cause lower but not total prevention of transcription. D -
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correct answer; if the inducer is totally ineffective, then the repressor will permanently bind to operato
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r and totally prevent transcription.
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The regulatory elements in the lacBoperon act to:
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A. Repress transcription when there is no lactose present B. Repress transcription when there is lactose
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present C. Activate transcription when there is no glucose present D. Activate transcription when there i
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s glucose present E. A and C - correct answer-
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E Explanation: The cell wants to both repress transcription when there is no lactose present and activate
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it when glucose is absent (C "slightly less good" answer than A, but still true). Similar to Clicker Questio
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n6
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A bacterium needs to make a certain lipid that it cannot obtain from its environment. That same lipid is
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involved in regulating the expression of the enzymes that make it. Which of the following is the most lik
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ely regulatory function of the lipid?
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A. Effector B. Activator C. Inducer D. Co-repressor E. Operator - correct answer-
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D Explanation: If you have that lipid, you would want it to not make any more. So, if you have the lipid i
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n the cell, you would want to turn off the transcription, so it would likely be involved in negative
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regulati on. Effectors and activators are both involved in positive regulation. An inducer is under negative
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regulat ion but itsBjob is to turn on transcription. A co-
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repressor will only turn the gene off if there is a signal the cell can sense. Operator is a piece of DNA.
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A bacterium is unable to transport lactose into the cell to be broken down. Which gene is likely mutated
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in this bacterium?
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