Ch. 18 Study Module

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1

What is the mutant phenotype of bacteria that lack a functional lacY gene?

They do not accumulate lactose inside the cell.

2

The lactose operon is likely to be transcribed when __________.

the cyclic AMP and lactose levels are both high within the cell

3

Which of the following best describes regulons?

A set of separate genes or operons that contain the same regulatory sequences and are controlled by a single type of regulatory protein

4

Which of the following statements about AraC’s regulation of the ara operon is true?

Increasing the concentration of arabinose would increase the production of the AraB protein.

5

What molecule acts as an inducer of lac operon transcription?

Lactose

6

Gene expression can be controlled at which of these levels?

  1. Transcription
  2. Translation
  3. Post-translation
7

How can the AraC protein act as both a transcriptional activator and an inhibitor for the ara operon?

When AraC is bound to arabinose, it stimulates transcription. In the absence of arabinose, AraChas a different conformation that results in transcriptional repression of this operon.

8

best summarizes how the lacoperon is regulated?

Positive and negative control elements regulate the lac operon.

9

Regulons can work through negative control using __________ and positive control using __________.

repressors; activators

10

Genes that are transcribed constitutively are said to be __________.

transcribed all the time

11

In the lac operon, the repressor protein is encoded

lacI

12

Why is the lacI mutant a constitutive mutant?

The mutant cells do not need an inducer to express β-galactosidase.

13

When lactose levels are low, which statement is true about the levels of transcription from the lacI gene?

lacI transcription is unaffected.

14

Which of the following experiments would help determine whether the β-galactosidase gene is induced by lactose or glucose?

Measure the amount of β-galactosidase produced by E. coli grown on a glucose plate, a lactose plate, and a glucose + lactose plate.

15

For an operon under negative control to be transcribed, which of the following must occur?

RNA polymerase must bind to the promoter, and the repressor must be inactive.

16

What type of regulation is the ara operon under when arabinose is present?

Positive Control

17

What effects will growth in glucose and lactose have on E. colisugar metabolism and gene expression?

  • The bacteria will use glucose as their primary sugar source until it is used up, and then switch to lactose.
18

Negative control of transcription occurs when a/an __________, a regulatory protein, binds to DNA and shuts down transcription.

repressor

19

Which of the following describes post-translational control?

  • Post-translational control provides the most rapid response because only one step is needed to activate or inactivate an existing protein.
20

In the lac operon, genes are regulated by which of the following?

Negative as well as positive control

21

Which molecule acts as an inducer of lac operon transcription?

Lactose