Deck 17: Regulation of Gene Expression in Bacteria and Bacteriophages

Question 1

The inducer of the lac operon is

A)galactose.
B)glucose.
C)allolactose.
D)repressor protein.
E)permease.

Answer 1

C

Question 2

What is the underlying reason that a lambda phage would need to switch from the lysogenic state to the lytic state?

A)To have its genome replicated
B)To kill its host cell
C)To make more of the Cro protein
D)To be more efficient in its use of resources
E)To escape an endangered host cell

Answer 2

E

Question 3

Attenuation of the trp operon fails to occur when

A)a lack of tryptophan causes stalling of ribosomes on the leader sequence of the RNA.
B)an RNA stem-loop forms that allows transcription to continue.
C)an RNA stem-loop that causes transcription to terminate fails to form.
D)the cell has enough tryptophan.
E)the operator is mutated.

Answer 3

D

Question 4

The order of the structural genes in the lac operon is

A)5'-lacY-lacZ-lacA-3'.
B)3'-lacZ-lacY-lacA-5'.
C)5'-lacZ-lacY-lacA-3'.
D)3'-lacY-lacA-lacZ-5'.
E)5'-lacA-lacY-lacZ-3'.

Question 5

The interaction between allolactose and the repressor protein results in a shape change known as a(n)

A)isomer.
B)mutation.
C)enantiomer.
D)allosteric shift.
E)transformant.

Question 6

Which positive regulatory protein is required for the production of phage coat protein in lambda?

A)CI
B)Cro
C)N
D)Q
E)None of these

Question 7

To inhibit the transcription of operon genes,the lacI gene product binds to

A)the operator.
B)the promoter.
C)the repressor.
D)the inducer.
E)β-galactosidase.

Question 8

In terms of regulation of gene expression,tryptophan and allolactose are examples of ________ molecules.

A)repressor
B)effector
C)inducer
D)operator
E)terminator

Question 9

In bacteriophage lambda,the establishment of lysogeny requires the protein product of which gene?

A)N
B)cII
C)cIII
D)B and C only
E)A,B,and C

Question 10

Which of the following can be a transdominant mutation in partial diploid cells?

A)lacZ^-
B)P_lacI^-
C)lacI^S
D)lacY^-
E)lacI^-

Question 11

A lacO^C mutation is

A)constitutive.
B)cis-dominant.
C)incompletely dominant.
D)codominant
E)recessive.

Question 12

Which of the following mutations is dominant over wild-type lacI⁺ in a partial diploid experimental cell?

A)lacA^-
B)lacO^-
C)lacI^-
D)lacI^S
E)C and Donly

Question 13

Operons can best be defined as

A)operational mutations affecting gene expression.
B)a set of genes under common regulatory control.
C)dominant alleles responsible for enzyme synthesis.
D)a balance between repressor and inducer molecules.
E)a common mode of gene expression in bacteria.

Question 14

The genetic switch for the infection pathways of lambda phage is controlled by two regulatory proteins: ________ and ________.

A)lambda repressor,Cro
B)lambda repressor,permease
C)excisionase,integrase
D)recA,Cro
E)lyase,lysogenase

Question 15

The ________ pathway in lambda phage leads to integration of viral DNA with that of the host,while the ________ pathway leads to induction of progeny viruses.

A)lytic,lysogenic
B)invasive,replicative
C)repressive,inductive
D)lysogenic,lytic
E)replicative,lysogenic

Question 16

In the lac operon in E.coli,a nonsense mutation in the ________ gene will result in a loss of β-galactosidase activity in the cell.

A)lacZ
B)lacI
C)lacY
D)Both A and B
E)All of these

Question 17

To maintain lysogeny in lambda,which of the following needs to occur?

A)Binding of repressor protein to O_L
B)Binding of repressor protein to O_R
C)Inactivation of P_L
D)Inactivation of P_R
E)All of these

Question 18

How many structural genes are under the control of the trp operon promoter?

A)1
B)2
C)3
D)4
E)5

Question 19

During transcription of the trp operon,pairing of regions 2 and 3 in the leader peptide mRNA creates a(n)________ signal.

A)continuous
B)termination
C)antitermination
D)induction
E)repression

Question 20

Mutants that are lacI^S do not produce lac enzymes,regardless of the presence or absence of lactose.

Question 21

Briefly define what is meant by negative and positive control of the lac operon.

Question 22

Distinguish between cis- and trans-dominance.

Question 23

The use of CAP- cAMP complex as a positive regulator is specific to the lac operon.

Question 24

If a cell has the partial diploid genotype lacI⁺ lacO⁺ lacZ^- lacY^{+
_______________________}
lacI^- l acO⁺ lacZ⁺ lacY^{- ,}
how will its gene expression in the presence of allolactose?

Question 25

lacI^S encodes superrepressors,repressors that always bind to the operator and prevent gene transcription.

Question 26

A constitutive gene is a gene that is occasionally expressed.

Question 27

Why do lacO^C mutants express in cis-dominant and not in transdominant fashion?

Question 28

The purpose of regulation of the trp operon in bacteria is to ensure the cell can digest tryptophan if it is present and the cell is short on energy.

Question 29

Compare the action of repressor proteins in the lac operon and the trp operon.

Question 30

What selective pressures are likely to have led to the evolution of regulatory systems like operons? Why not simply express these genes continuously?

Question 31

Attenuation in trp gene regulation is accomplished by

A)reducing permeability of tryptophan,the effector molecule.
B)blocking expression of trp mRNA.
C)formation of secondary mRNA structures in the leader region.
D)binding with RNA polymerase.
E)repression of the trp operator.

Question 32

How are partial diploid E.coli constructs made?

Question 33

The enzyme transacetylase is responsible for uptake of lactose.

Question 34

Genes required for maintaining basic cell structure,growth,and division are housekeeping genes and have regulated expression.

Question 35

The tryptophan codons of the attenuator sequence help speed up transcription of downstream trp genes at high concentrations of tryptophan.

Question 36

Mutations of lacO^C lead to attenuated expression of lac structural genes.

Question 37

For each of the following lac operon mutations,state whether transcription of β-galactosidase will increase,decrease,or be unaffected.
a.P_lac^-
b.lacY⁺
c.lacI^-
d.lacO^-
e.lacA^-

Question 38

The structural genes in the lac operon are transcribed into a single polycistronic mRNA molecule.

Question 39

If a cell has the partial diploid genotype lacI⁺ lacO^- lacZ⁺ lacY^{+
______________________}
lacI^- lacO^- lacZ⁺ lacY^{- ,}
how will its gene expression function in the presence of allolactose?

Question 40

Contrast negative (repressor)and positive (CAP)control in the lac operon.

Question 41

Microbial genomics is a rapidly growing field.Of great interest to geneticists is the search for new operons as new microbial genome sequences become available.What kind of "signature" or identifying feature would you look for as you searched new genomes for candidate operons?

Question 42

Should viruses like lambda phage be considered living entities? Or are they more properly viewed as parasitic fragments of DNA?

Question 43

At the molecular level,how do proteins like repressors bind to DNA? How can binding affinities be increased or decreased?

Question 44

What effect would mutational damage of the following genes or gene regions have on the induction of an integrated lambda phage virus?
a.damage to the cI gene
b.damage to the cro gene
c.damage to the xis gene

Question 45

Give an overview of the mechanism by which ultraviolet radiation induces the lytic pathway in lambda phage.