Deck 19: DNA Mutation, DNA Repair, and Transposable Elements

Question 1

Operons can best be defined as

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

Answer 1

E

Question 2

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

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

Answer 2

E

Question 3

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

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

Answer 3

C

Question 4

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

A) lacIS
B) PlacI-
C) lacZ-
D) lacI-
E) lacY-

Question 5

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

A) lacIS
B) lacA-
C) lacI-
D) lacO-
E) C and D

Question 6

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

A) One
B) Two
C) Three
D) Four
E) Five

Question 7

A mutation in which of the following locations would lead to constitutive expression of the lac genes?

A) lac promoter
B) lacZ
C) lacI
D) lacO
E) C or D

Question 8

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

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

Question 9

Attenuation in trp gene regulation is accomplished by

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

Question 10

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

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

Question 11

A lacOC mutation is

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

Question 12

Induction of the lac operon occurs when the repressor protein undergoes a(n)

A) transacetylation.
B) methylation.
C) allosteric shift.
D) mutation.
E) All of the above

Question 13

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

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

Question 14

To maintain lysogeny in lambda, enough repressor must be present to bind to

A) OR2 only.
B) OR1 and OR2.
C) OR2 and OR3.
D) OR1 only.

Question 15

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

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

Question 16

The order of the structural genes in the lac operon is

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

Question 17

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

Question 18

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

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

Question 19

The inducer of the lac operon is

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

Question 20

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

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

Question 21

Why do lacOC mutants express in cis-dominant and not in transdominant fashion?

Question 22

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

Question 23

A constitutive gene is a gene that is occasionally expressed.

Question 24

In bacteriophages, the lytic pathway precedes the lysogenic pathway.

Question 25

Distinguish between cis- and transdominance.

Question 26

Outline the role of attenuator sequences 1, 2, 3, and 4 in the leader peptide-coding region of the trp operon.

Question 27

How are partial diploid E. coli constructs made?

Question 28

The enzyme transacetylase is responsible for uptake of lactose.

Question 29

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

Question 30

Given the partial diploid genotype lacI+ lacO- lacZ+ lacY+ lacI- lacO- lacZ+ lacY- How will this cell function in terms of gene expression in the presence of allolactose?

Question 31

At low concentrations of tryptophan, trp genes are expressed maximally.

Question 32

Mutations of lacOC lead to attenuated expression of lac structural genes.

Question 33

Given the partial diploid genotype lacI+ lacO+ lacZ- lacY+ lacI- lacO+ lacZ+ lacY- How will this cell function in terms of gene expression in the presence of allolactose?

Question 34

lacIS encodes superrepressors, repressors that always bind to the operator and prevent gene transcription.

Question 35

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

Question 36

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 37

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

Question 38

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

Question 39

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

Question 40

Amino acid biosynthesis operons in which gene activity is repressed when a chemical (e.g., an amino acid) is added to the medium are termed repressible operons.

Question 41

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

Question 42

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 (see, for example, Ermolaeva, White, and Salzberg. 2001. Prediction of operons in microbial genomes. Nucleic Acids Res. 29:1216-1221; PMID: 11222772). What kind of "signature" or identifying feature would you look for as you searched new genomes for candidate operons?

Question 43

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