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Essentials of Genetics

William S. Klug, Michael R. Cummings, Charlotte A. Spencer

Chapter 15

Regulation of Gene Expression in Bacteria - all with Video Answers

Educators

Chapter Questions

01:05

Problem 1

In this chapter, we focused on the regulation of gene expression in bacteria. Along the way, we found
many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions?
(a) How do we know that bacteria regulate the expression of certain genes in response to the environment?
(b) What evidence established that lactose serves as the
inducer of a gene whose product is related to lactose metabolism?
(c) What led researchers to conclude that a repressor molecule
regulates the lac operon?
(d) How do we know that the lac repressor is a protein?
(e) How do we know that the trp operon is a repressible control system, in contrast to the lac operon, which is an inducible control system?

Jennifer Stoner
Jennifer Stoner
Numerade Educator
00:45

Problem 2

Review the Chapter Concepts list on p. $285 .$ These all relate to the regulation of gene expression in bacteria. Write a brief essay that discusses why you think regulatory systems evolved in bacteria (i.e., what advantages do regulatory systems provide to these organisms?), and, in the context of regulation, discuss why genes related to common functions are found together in operons.

Jennifer Stoner
Jennifer Stoner
Numerade Educator
01:24

Problem 3

Contrast positive versus negative control of gene expression.

VS
Vivek Singh
Numerade Educator
02:56

Problem 4

Contrast the role of the repressor in an inducible system and in a repressible system.

Bryan Lynn
Bryan Lynn
Numerade Educator
06:00

Problem 5

For the lac genotypes shown in the following table, predict whether the structural genes ( $Z$ ) are constitutive, permanently repressed, or inducible in the presence of lactose.

Jenny Wu
Jenny Wu
Numerade Educator
00:59

Problem 6

For the genotypes and conditions (lactose present or absent) shown in the following table, predict whether functional enzymes, nonfunctional enzymes, or no enzymes are made.

Emily Himsel
Emily Himsel
Numerade Educator
01:11

Problem 7

The locations of numerous $\operatorname{lac} I^{-}$ and $\operatorname{lac} I^{S}$ mutations have been determined within the DNA sequence of the lacI gene. Among these, lacI - mutations were found to occur in the $5^{\prime}$ -upstream region of the gene, while $l a c I^{S}$ mutations were found to occur farther downstream in the gene. Are the locations of the two types of mutations within the gene consistent with what is known about the function of the repressor that is the product of the lacI gene?

Precious
Precious
Numerade Educator
03:08

Problem 8

Describe the experimental rationale that allowed the lac repressor to be isolated.

Sulav Pokhrel
Sulav Pokhrel
Numerade Educator
05:49

Problem 9

What properties demonstrate that the lac repressor is a protein? Describe the evidence that it indeed serves as a repressor within the operon system.

Dennis Howard
Dennis Howard
Numerade Educator
01:56

Problem 10

Predict the effect on the inducibility of the lac operon of a mutation that disrupts the function of (a) the crp gene, which encodes the CAP protein, and (b) the CAP-binding site within the promoter.

Dennis Howard
Dennis Howard
Numerade Educator
02:22

Problem 11

Erythritol is a natural sugar abundant in fruits and fermenting foods. Pathogenic bacterial strains that catabolize erythritol contain four closely spaced genes, all involved in erythritol metabolism. One of the four genes (eryD) encodes a product that represses the expression of the other three genes. Erythritol catabolism is stimulated by erythritol. Present a regulatory model to account for the regulation of erythritol catabolism in such bacterial strains. Does this system appear to be under inducible or repressible control?

Dennis Howard
Dennis Howard
Numerade Educator
03:05

Problem 12

Describe the role of attenuation in the regulation of tryptophan biosynthesis.

Dennis Howard
Dennis Howard
Numerade Educator
02:23

Problem 13

What is the major difference between the mechanism involved in attenuation and riboswitches and the mechanism involved in the
regulation of the lactose operon?

JH
Josh Hill
Numerade Educator
02:22

Problem 14

A bacterial operon is responsible for the production of the biosynthetic enzymes needed to make the hypothetical amino acid tisophane (tis). The operon is regulated by a separate gene, $R$ The deletion of $R$ causes the loss of enzyme synthesis. In the wildtype condition, when tis is present, no enzymes are made; in the absence of tis, the enzymes are made. Mutations in the operator gene $\left(O^{-}\right)$ result in repression regardless of the presence of tis. Is the operon under positive or negative control? Propose a model for (a) repression of the genes in the presence of tis in wild-type cells and (b) the mutations.

Dennis Howard
Dennis Howard
Numerade Educator
01:15

Problem 15

Bacterial sRNAs can bind to mRNAs through complementary binding to regulate gene expression. What determines whether the sRNA/mRNA binding will promote or repress mRNA translation?

Shazia Naz
Shazia Naz
Numerade Educator
01:07

Problem 16

Why is the CRISPR-Cas system of bacteria considered an adaptive immunity rather than an innate immunity?

Sarah Bennett
Sarah Bennett
Numerade Educator
04:07

Problem 17

How does the molecular mechanism of the CRISPR-Cas system use a viral DNA sequence against that same virus?

Kendrick Buford
Kendrick Buford
Numerade Educator
02:07

Problem 18

In the publication that provided the first evidence of CRISPRCas as an adaptive immune system [Barrangou, R., et al. (2007). Science. $315: 1709-1712$ ], the authors state that CRISPR-Cas "provides a historical perspective of phage exposure, as well as a predictive tool for phage sensitivity." Explain how this is true using what you know about the CRISPR locus.

Kendrick Buford
Kendrick Buford
Numerade Educator