Deck 16: Regulation of Gene Expression in Bacteria

Question 1

Usually,bacteria only make tryptophan when tryptophan is absent or available in low concentration.However,a particular bacterial mutation makes tryptophan all the time whether or not tryptophan is present.What could explain this phenotype?

A)the terminator hairpin is unable to form
B)trpD is mutated
C)trpA is mutated
D)the antiterminator hairpin is unable to form
E)trpE is mutated

Answer 1

A

Question 2

Through genetic analysis,Jacob and Manod were able to make predictions about the lac operon.However,which of the following techniques confirmed their predictions?

A)crystal structure analysis
B)CRISPR
C)recombinant DNA technology
D)PCR
E)DNA sequencing

Answer 2

A

Question 3

lacI codes for an__________,and when lacI is mutated,the lac operon is __________.

A)repressor; never expressed
B)repressor; constitutively expressed
C)structural gene; never expressed
D)activator; constitutively expressed
E)activator; never expressed

Answer 3

repressor; constitutively expressed

Question 4

What term refers to clusters of bacterial genes that are under the control of a single regulatory region?

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

Question 5

Some lac operon mutations allow for beta galactosidase to be expressed constitutively even in the absence of lactose.Which of the following lac genotypes would allow for this constitutive expression?

A)I⁺ P⁺ O⁺ Z^- Y⁺ A⁺
B)I^s P⁺ O⁺ Z⁺ Y⁺ A⁺
C)I⁺ P^- O⁺ Z⁺ Y⁺ A⁺
D)I⁺ P⁺ O^c Z⁺ Y⁺ A⁺
E)I⁺ P⁺ O⁺ Z⁺ Y⁺ A⁺

Question 6

What is the name of the molecule that binds to CAP to activate transcription of the lac operon?

A)galactose
B)ATP
C)cAMP
D)lactose
E)glucose

Question 7

Which binds to the operator of the lac operon?

A)permease
B)repressor
C)activator
D)lactose
E)beta galactosidase

Question 8

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

A)splitting the linkage of lactose to produce glucose and galactose
B)binding to the operator of the lac operon
C)transporting lactose into the cell
D)forming lactose from two glucose molecules
E)forming ATP from pyruvate

Question 9

Small noncoding RNAs regulate gene expression in bacteria by __________ .

A)repressing transcription
B)activating translation
C)activating transcription
D)by both inhibiting and activating translation
E)inhibiting translation

Question 10

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

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

Question 11

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

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

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,__________.

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

Question 13

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

Question 14

A protein,like the lac repressor,is said to be __________because when it binds lactose,it structurally changes and its chemical activity also changes.

A)multimeric
B)structural
C)allosteric
D)enzymatic
E)digestive

Question 15

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

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

Question 16

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

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

Question 17

Enzymes that are continuously produced are said to have an__________expression.

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

Question 18

When both lactose and glucose are available to E.coli,which part of the lac operon regulation assures that glucose will be metabolized first?

A)CAP binds to cAMP and then to the promoter only in the presence of low glucose.
B)The repressor cannot bind to the operator in the presence of lactose.
C)Permease allows lactose to enter the cell when lactose enters the cell.
D)The repressor binds to the operator in the absence of lactose.
E)RNA polymerase transcribes the lac operon to make a single RNA molecule.

Question 19

To translate the three enzymes of the lac operon,__________mRNA molecules is/are transcribed.

A)3
B)0
C)2
D)4
E)1

Question 20

If lactose is accumulating outside of E.coli and is unable to enter,then which structural gene of the lac operon is most likely mutated?

A)lacY
B)lacX
C)lacZ
D)lacI
E)lacA

Question 21

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 22

The terminating "hairpin" loop occurs in the trp operon when sufficient tryptophan is present.

Question 23

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 24

A constitutive mutation in the lac operon may be of several types.Name two types of constitutive mutations and explain why they are constitutive.

Question 25

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

Question 26

What is an allosteric molecule?

Question 27

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

Question 28

The accompanying table lists several genotypes associated with the lac operon in E.coli.For each,indicate with a "+" or a "-" whether fi- galactosidase would be expected to be produced at induced levels. I⁺ = wild- type repressor
I^- = mutant repressor unable to bind to the operator)I^s = mutant repressor insensitive to lactose)
O⁺ = wild- type operator
O^c = constitutive operator insensitive to repressor)

Question 29

When lactose is first introduced into the medium,the lac operon is not induced and thus permease isn't induced.How it is possible for lactose to enter the cell before the lac operon is induced?

Question 30

The table below lists several genotypes associated with the lac operon in E.coli.For each,indicate with a "+" or a
"-" whether functional fi- galactosidase would be expected to be produced at induced levels. I⁺ = wild- type repressor
I^- = mutant repressor unable to bind to the operator)
I^s = mutant repressor insensitive to lactose)
O⁺ = wild- type operator
O^c = constitutive operator insensitive to repressor)

Question 31

In the accompanying diagram,what type of control,positive or negative,is operating? The oval structure is RNA polymerase.

Question 32

Present an overview of bacterial gene regulation in terms of growth efficiency.

Question 33

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 fi- galactosidase in the lac system.
d)Show by diagram the manner in which lactose brings about transcription of the three structural genes of the operon.
e)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).

Question 34

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.

Question 35

Explain why lacO^c mutations are cis- acting while lacI mutations can be trans- acting.

Question 36

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 37

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

Question 38

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

Question 39

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

Question 40

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 41

Explain how small noncoding RNAs sRNAs)can function as both a negative regulator and a positive regulator.