Question 1

Which of the following terms best characterizes catabolite repression associated with the lac operon in E. coli?

Accepted Answer

Catabolite repression is a form of positive control because it involves the cAMP-CRP complex enhancing the transcription of the lac operon when glucose levels are low.

Question 2

Present a detailed description of the actions of the regulatory proteins in inducible and repressible enzyme systems.

Accepted Answer

Inducible system: The repressor is normally active, but the inducer inactivates the repressor. Repressible system: The repressor is inactive but is activated by the corepressor. Active repressors turn off transcription.

Question 3

(a) Describe by labeled diagram the structural components of the lac operon in E. coli.
a() State the function of the lac regulator gene.
b() State the function of fi -galactosidase in the lac system.
c() Show by diagram the manner in which lactose brings about transcription of the three structural genes of the lac operon.
d() Explain why certain mutations in the regulator gene (I -) of the lac system result in maximal synthesis of fi -galactosidase, permease, and transacetylase even in the
absence of the inducer (lactose).

Accepted Answer

(a) See appropriate diagrams in the text.
a() The regulator gene produces a repressor protein that interacts with the operator to shut off transcription. In the presence of lactose, the repressor protein does not interact with the operator.
b() fi -galactosidase cleaves the lactose sugar into its components, glucose and galactose.
c() See appropriate diagrams in the text.
d() Such mutations provide modified proteins that are unable to associate with the operator to shut off transcription.

Question 4

In the diagram below, what type of control, positive or negative, is operating?

Accepted Answer

The answer of In the diagram below, what type of...

Question 5

Compare and contrast positive and negative control of gene expression in bacteria.

Accepted Answer

The answer of Compare and contrast positive and negative control...

Question 6

Regarding eukaryotic and prokaryotic genetic regulation, what process seems to be the most similar between the two?

Accepted Answer

Both eukaryotic and prokaryotic organisms regulate gene expression at the transcriptional level, although the mechanisms and complexity may differ.

Question 7

What is the function of the lacY gene in the lac operon?

Accepted Answer

The answer of What is the function of the lacY...

Question 8

Which of the following clusters of terms applies when addressing enhancers as elements associated with eukaryotic genetic regulation?

Accepted Answer

Enhancers are cis-acting elements that can function in variable orientations and positions relative to the genes they regulate.

Question 9

Genetic regulation in eukaryotes can take place at a variety of levels from transcriptional to posttranslational. At what level is genetic regulation considered most likely in prokaryotes?

Accepted Answer

In prokaryotes, genetic regulation primarily occurs at the transcriptional level, as they lack the complex post-transcriptional modifications found in eukaryotes, such as capping, exon processing, intron processing, and polyadenylation.

Question 10

Which term most appropriately refers to a regulatory protein in prokaryotes?

Accepted Answer

DNA binding proteins in prokaryotes, such as repressors and activators, regulate gene expression by binding to specific DNA sequences.

Question 11

Which term would be applied to a regulatory condition that occurs when protein is associated with a particular section of DNA and greatly reduces transcription?

Accepted Answer

Negative control refers to a regulatory condition where a protein binds to a specific DNA region and inhibits transcription.

Question 12

When referring to attenuation in regulation of the trp operon, it would be safe to say that when there are high levels of tryptophan available to the organism, _.

Accepted Answer

When tryptophan levels are high, the ribosome quickly translates the leader peptide, allowing the formation of a terminator hairpin in the mRNA, leading to transcriptional termination.

Question 13

In the lac operon, the product of structural gene lacZ is capable of _.

Accepted Answer

The lacZ gene encodes the enzyme β-galactosidase, which is responsible for cleaving the β-linkage in lactose to produce glucose and galactose.

Question 14

Two modular elements that appear as consensus sequences upstream from RNA polymerase II transcription start sites are _.

Accepted Answer

The TATA box and CAAT box are consensus sequences found upstream of the transcription start site in eukaryotic genes transcribed by RNA polymerase II. They play crucial roles in the initiation of transcription.

Question 15

A constitutive mutation in the lac operon may be of several types. Name two types of constitutive mutations.

Accepted Answer

The answer of A constitutive mutation in the lac operon...

Question 16

Which term refers to a contiguous genetic complex that is under coordinated control?

Accepted Answer

An operon is a contiguous genetic complex that is under coordinated control.

Question 17

Explain why lacOc mutations are cis -acting, whereas lacI mutations can be
trans -acting.

Accepted Answer

The answer of Explain why lacOc mutations are cis -acting,...

Question 18

DNA methylation may be a significant mode of genetic regulation in eukaryotes. Methylation refers to _.

Accepted Answer

DNA methylation involves the addition of methyl groups to the cytosine bases in CG dinucleotides, affecting gene expression.

Question 19

Certain mutations in the regulator gene of the lac system in E. coli result in maximal
synthesis of the Lac proteins (fi -galactosidase, etc.) even in the absence of the inducer (lactose). Provide an explanation for this observation.

Accepted Answer

The answer of Certain mutations in the regulator gene of...

Question 20

Present an overview of prokaryotic regulation in terms of growth efficiency.

Accepted Answer

The answer of Present an overview of prokaryotic regulation in...

Quiz 15: Regulation of Gene Expression