ASU BIO 340 Exam 3 | WITH
QUESTIONS AND ANSWERS 100%
VERIFIED
Question 1: What will be the effect on transcription when an
inhibitor is in play?
- Allow transcription B. Prevent transcription
CORRECT 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.
Question 2: What will be the effect on transcription when an
inducer is in play?
- Allow transcription B. Prevent transcription
CORRECT ANSWER : A
Explanation: When an inducer is in play, it will allow
transcription.
Question 3: For a gene under positive control, which of the
following would prevent transcription?
- Repressor B. Corepressor C. Inducer D. Effector E.
Inhibitor
CORRECT ANSWER : E
Explanation: Positive regulation includes activators (affected
by effectors and inhibitors); inhibitors prevent activator from binding to DNA, thus preventing transcription.
Question 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?
- Repressor B. Corepressor C. Inducer D. Effector E.
Inhibitor
CORRECT 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.
Question 5: Which molecule serves as the inducer for the lac
operon?
- cAMP B. Glucose C. Lactose D. Allolactose
CORRECT ANSWER : D
Explanation: Allolactose is the molecule that binds to
repressor protein, making it unable to bind to the operator.
Question 6: Which of the following conditions will result in
the greatest levels of transcription of the lac operon?
- Lactose absent, glucose absent B. Lactose absent, glucose
present C. Lactose present, glucose present D. Lactose present, glucose absent
CORRECT 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.
Question 7: Which of the following mutations will result in
the lowest level of transcription of the lac operon when lactose is present?
- 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
CORRECT 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