Deck 6: Microviruses

Question 1

Which of the following describes the first step in the replication cycle of the phage fX174?

A) Conversion of ssDNA into dsDNA.
B) Translation of the viral genome into protein.
C) Transcription of the viral DNA by the cellular RNA polymerase.
D) Transcription of the viral DNA by the viral RNA polymerase.
E) Integration of the viral DNA into the host chromosome.

Answer 1

A

Question 2

Why must the microviruses produce dsDNA before viral genes can be expressed?

A) Only dsDNA can be packaged into virions.
B) DsDNA is more stable than ssDNA.
C) Only dsDNA is a substrate for transcription by the host RNA polymerase.
D) Only dsDNA is a substrate for replication by the host DNA polymerase.
E) The viral regulatory proteins can only bind to double-stranded DNA.

Answer 2

C

Question 3

Which of the following was used to distinguish different bacteriophages before the development of the electron microscope in the 1930's?

A) Western blot
B) DNA sequence
C) DNA restriction analysis
D) X-ray crystallography
E) Plaque morphology

Answer 3

E

Question 4

Which of the following bacteriophages had its entire genome sequenced first?

A) MS2
B) fX174
C) Lambda phage
D) T4
E) T3

Question 5

The A protein of the phage fX174 is required for which of the following processes?

A) Synthesis of the double-stranded replicative form DNA.
B) Packaging of the viral protein into the newly formed capsids.
C) Assembly of the viral capsid.
D) Synthesis of the plus-strand DNA via rolling circle replication.
E) Entry of the viral DNA into the host cell.

Question 6

Because gokushoviruses infect bacteria that can parasitize eukaryotic cells, they may have been the evolutionary source for eukaryotic viruses.

Question 7

What distinguishes the small bacteriophage fX174 from many other bacteriophages?

A) The virion has a very large head.
B) The virion has a very long tail.
C) It has a single-strand DNA genome.
D) It has a single-strand RNA genome.
E) It has a double-strand RNA genome.

Question 8

Stage I DNA replication in the bacteriophage fX174 is carried out entirely by host cell proteins.Why?

A) DNA replication is required for penetration of the viral genome into the host cell.
B) The bacteriophage fX174 does not encode any of its own DNA replication proteins.
C) The phage genome has become integrated into the host genome.
D) Only the host cell proteins can replicate a ssDNA genome.
E) Stage I DNA replication occurs before any viral proteins are expressed.

Question 9

Which of the following statements is NOT true?

A) Both microviruses and gokushoviruses package a ssDNA genome.
B) Microviruses use two different scaffolding proteins while gokushoviruses only use one.
C) The genomes of the gokushoviruses are much smaller than the microviruses.
D) Both microviruses and gokushoviruses infect free living bacterial cells.
E) Both microviruses and gokushoviruses package their genomes into small icosahedral capsids.

Question 10

The phage fX174 can tolerate mutations in the non-structural region of its genome more easily than in the structural region of the genome.Which of the following explains why?

A) Not all of the proteins coded in this region are packaged into the mature capsid.
B) Single-stranded DNA is not as easily mutated as double-stranded DNA.
C) Many of the non-structural proteins have more than one function.
D) Some of the non-structural proteins are non-essential for virus replication.
E) The presence of overlapping reading frames in this region of the genome.

Question 11

Which of the following is used as the primary host cell receptor for the phage fX174?

A) Glucose on lipopolysaccharide
B) A membrane protein
C) The cell wall
D) The F-pili
E) The internal membrane

Question 12

Which of the following bacteriophages has a genome composed of ssDNA?

A) lambda phage
B) fX174
C) T7
D) MS2
E) Qb

Question 13

In the bacteriophage fX174, which of the following events occurs at the same time as the ssDNA is packaged into the procapsid?

A) Proteolytic maturation of the capsid proteins.
B) Removal of the external scaffolding protein D.
C) Removal of the internal scaffolding protein B.
D) Addition of the spike proteins to the capsid.
E) Synthesis of the second DNA strand.

Question 14

How does the E protein cause lysis of the host cell?

A) It degrades the cell wall components before cell wall assembly.
B) It makes the cell wall more resistant to osmotic pressure.
C) It breaks critical bonds in the cell wall components.
D) It activates a cellular enzyme that can break down the cell wall.
E) It inhibits a cellular protein that synthesizes the cell wall.

Question 15

Entry of the viral genome for fX174 appears to occur at which locations on the host cell?

A) The surface of the F-pili
B) Cell wall adhesion regions
C) The base of the flagella
D) Regions of high lipopolysaccharide
E) All of the above

Question 16

When is the external scaffolding protein D removed from the procapsid?

A) After lysis of the host cell
B) During packaging of the viral DNA into the procapsid.
C) When the internal scaffolding protein B is removed from the procapsid.
D) Before the viral DNA is package into the procapsid
E) During entry into the next host cell

Question 17

Which of the following processes was studied by working with the phage fX174?

A) Transcription of mRNA
B) Splicing of mRNA
C) Translation of mRNA
D) Replication of DNA
E) Lysogeny

Question 18

Abundant synthesis of the E protein from the bacteriophage fX174 would lead to premature lysis of the host cell.Which of the following mechanisms controls the synthesis of the E protein?

A) The mRNA is transcribed from a weak promoter.
B) The open reading frame has a weak ribosome binding site.
C) The secondary structure of the mRNA prevents translation of the E protein.
D) The repressor protein prevents transcription of the mRNA.
E) There is a strong transcriptional terminator upstream of the E gene.

Question 19

Which of the following describes the function of the H protein (pilot protein)in the microviruses?

A) It forms the spikes on the capsid.
B) It is the scaffolding protein for assembly.
C) It is carries out DNA replication.
D) It regulates mRNA transcription.
E) It helps the viral DNA enter the host cell.

Question 20

Several different mRNAs are produced from the fX174 genome using which of the following mechanisms?

A) Multiple transcription promoters
B) Multiple transcription terminators
C) Multiple translation start sites
D) Multiple stop codons
E) Both a and b are correct

Question 21

The scaffolding proteins of the bacteriophage fX174 remain as part of the final mature capsid structure.

Question 22

The genome of the fX174 phage is very compact and contains several overlapping open reading frames.Explain how this can be both an evolutionary advantage and disadvantage for the phage.

Question 23

Mutations in the internal scaffolding protein B of the ssRNA phage fX174 cause abnormally small 9S and 6S particles to form in infected cells.Explain how this provides information about the assembly pathway of this virus.

Question 24

The bacteriophage fX174 has several weak transcriptional terminators which leads to mRNAs with different 5' ends.

Question 25

Describe the proteins required for both Stage I DNA and Stage II DNA replication and the role that each plays in the virus replication cycle of the bacteriophage fX174.

Question 26

Microviruses are the only known non-satellite viruses requiring two separate scaffolding proteins.

Question 27

The ssDNA phage fX174 does not encode DNA binding proteins to regulation gene expression from the viral genome.