Deck 16: Regulation of Gene Expression in Prokaryotes

Question 1

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

A) nonautonomous replication
B) forming lactose from two glucose molecules
C) replacing hexokinase in the early steps of glycolysis
D) splitting the -linkage of lactose
E) forming ATP from pyruvate

Answer 1

D

Question 2

The table below lists several genotypes associated with the lac operon in E.coli.For each,indicate with a "+" or a "-" whether functional β-galactosidase would be expected to be produced at induced levels.

Answer 2

(a) - + (b) + +
(c) + + (d) + +

Question 3

The ara operon is controlled by a regulator protein that exerts ________.

A) induction and expression
B) expressivity and penetrance
C) positive and negative control
D) upward and reverse control
E) top and bottom control

Answer 3

C

Question 4

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

Question 5

Genetic regulation in prokaryotes can involve alterations in RNA secondary structure.What phenomenon occurs in the trp operon that involves such alterations?

A) transcription
B) capping
C) polyadenylation of the 3′ end of the mRNAs
D) intron processing
E) attenuation

Question 6

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

Question 7

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,________.

A) the trp operon is being transcribed at relatively high levels
B) translational termination is likely
C) transcriptional termination is likely
D) tryptophan is inactivating the repressor protein
E) ribosomes are stalling during translation of the attenuator region

Question 8

What two important domains within a riboswitch involve the ligand-binding site?

A) aptamer and expression platform
B) A site and B site
C) B site and C site
D) alpha and beta
E) conformation and anticonformation

Question 9

The accompanying table lists several genotypes associated with the lac operon in E.coli.For each,indicate with a "+" or a "-" whether β-galactosidase would be expected to be produced at induced levels.

Question 10

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

Question 11

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

Question 12

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

A) inducible system
B) repressible system
C) negative control
D) positive control
E) constitutive

Question 13

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

A) negative control
B) positive control
C) induction
D) activation
E) stimulation

Question 14

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

Question 15

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

Question 16

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

Question 17

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

A) translation
B) RNA processing
C) DNA binding protein
D) gyrase action
E) helicase activation

Question 18

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

Question 19

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

A) lysogen
B) prototroph
C) operon
D) allosteric
E) attenuation

Question 20

Describe what is meant by a gratuitous inducer.Give an example.

Question 21

What experimental results would indicate that the mutation lacIˢ is dominant to lacI⁺?

Question 22

Regarding the trp operon,trpR- maps to a considerable distance from the structural genes.The mutation either inhibits the interaction with tryptophan or inhibits repressor formation entirely.In the presence of tryptophan in the medium,would you expect the trp operon to be transcriptionally active? Explain.

Question 23

The lac operon consists of three structural genes as well as the adjacent region of DNA known as the regulator.

Question 24

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

Question 25

What symbols are used to describe constitutive mutations at specific regions of the lac regulatory system?

Question 26

Monod discovered that if tryptophan is present in relatively high quantities in the growth medium,the enzymes necessary for its synthesis are repressed.How does this occur?

Question 27

What is an allosteric molecule?

Question 28

The catabolite repression system in E.coli essentially represses the lac operon when glucose is present.What evolutionary advantage would favor evolution of such a system?

Question 29

Regarding the lactose utilization system in E.coli,a gratuitous inducer is a molecule that is chemically analogous to lactose and induces the operon,but is not a substrate for the enzymes of the lac operon.

Question 30

State whether the following statement is true or false,then give your reasoning.The terminating "hairpin" loop occurs in the trp operon when sufficient tryptophan is present.

Question 31

Regarding the lactose utilization system in E.coli,a constitutive mutant is one in which the three enzymes are produced regardless of the presence or absence of lactose.

Question 32

The enzyme permease cleaves the linkage between glucose and galactose residues in lactose.

Question 33

The trp operon is typically characterized as being both under negative control and repressible.

Question 34

Describe the positive control exerted by the catabolite activating protein (CAP).Include a description of catabolite repression.

Question 35

Regarding regulation of the trp operon,what might one appropriately call the amino acid tryptophan?

Question 36

Under a system of negative control,genetic expression occurs unless such expression is shut off by some form of regulator.

Question 37

Within the control region of the trp operon is a section of DNA that is sensitive to levels of tryptophan in the system.What is the name of this region?

Question 38

Attenuation is known to occur in the lac operon.

Question 39

The cAMP-CAP complex and RNA polymerase bind more efficiently to the lac operon together than either does alone.What term is applied to this increased efficiency of binding?

Question 40

Under a system of positive control,transcription does not occur unless a regulator molecule directly stimulates RNA production.

Question 41

Attenuation involves the termination of mRNA synthesis.

Question 42

The trp and lac operons are both subject to forms of control that are typically called negative.