Chapter 13: Viruses, Viroids, and Prions

Which does not refer to the shape of a virus?

bacillus

Transducing virulent phages do not lyse the cells they invade because

bacterial DNA has replaced critical viral DNA in the phage

Viruses that infect bacterial cells are called ______.

bacteriophages

When the defective phage enters a new bacterial cell

both phage DNA and bacterial DNA integrate into the chromosome of the new cell host.

After entry of the bacteriophage into the host cell, a phage enzyme

breaks the host DNA into fragments.

A positive (+) strand of RNA

can directly act as mRNA.

When the bacteriophage transfers bacterial DNA into a recipient bacterial cell, this DNA

can integrate into the chromosome.

Expression of viral oncogenes in infected animal cells

can mimic proto-oncogenes, causing imbalance in cell cycle control towards unchecked proliferation, leading to tumor formation.

The shape of the virus is determined by its

capsid

Entry of bacteriophages and animal viruses into host cells

differs because bacteriophages leave the capsid outside the cell, while animal virus entry involves the entry of the whole nucleocapsid

If reasonably pure preparations of virus are available, the number of virus present may be determined by

electron microscopy

The phages T4 (lytic) and lambda (temperate) share all of the following characteristics EXCEPT

existing as a prophage

The receptors to which animal virus attachment proteins usually bind are

glycoproteins

The negative (-) sense strand of RNA

is used to synthesize more (+) strands.

In transduction, bacterial DNA is transferred to a new cell when

it is injected by the virus.

Resistance of some animals to certain viral diseases is based on

lack of specific receptors on the host cell

Bacteriophages involved in generalized transduction are ______ phages.

lytic

The term "segmented" refers to viruses that

may contain several pieces of RNA

Assembly of the T4 phage

may involve some self-assembly AND may involve the use of scaffolds

Outside of living cells, viruses are

metabolically inert

Prions affect the

nervous system

Using phages to treat a bacterial infection is an interesting idea because

of the increasing problem of antibiotic resistance in pathogens

In the process of specialized transduction

only a few specific genes from one bacterial cell are transferred to the second bacterial host by a phage.

In specialized transduction

only bacterial genes near the site of integration of the phage DNA can be transduced.

In latent infections, the virions are

only produced during reactivation

Bacteriophages adsorb or attach

only to members of the same bacterial species.

After host cell DNA is broken down by a viral enzyme

phage DNA is replicated and phage coat proteins are produced.

Spongiform encephalopathy occurs in all of the following EXCEPT

plants

A difference between plasmids and fragments of DNA that have been transferred between cells is

plasmids can replicate independently.

In the region of budding, the cytoplasmic membrane acquires

spike proteins AND matrix proteins

Attachment of animal viruses to the host cell may be by means of

spikes

The protein projections on the surface of a virus that are involved in attachment to the host cell are called

spikes

The genome of retroviruses is made of

ssRNA

The advantageous genes that can be transferred by transduction are genes for

sugar fermentation. toxin production. drug resistance.

What part of the attached bacteriophage enters through the host cell wall?

the nucleic acid

The integration of phage DNA into the bacterial chromosome occurs because of

the phage's ability to synthesize an enzyme that integrates its DNA into the host's chromosome

Plant viruses may be transmitted by

worms, contaminated seeds, humans, and insects

Plant viruses enter the host plant via

wound sites

Which of the following is used to classify viruses? i. Nucleic acid ii. Shape iii. Size iv. Host range v. Biochemical tests

(i), (ii), (iii), and (iv)

Prions

-composed of amino acids -cause disease in animals -inherited or consumed -Creutzfeldt-Jacob disease

Viroids

-composed of nucleotides -cause disease in plants -enter through wounds -Cadang-cadang

Transduction resulting from a packaging error.

Generalized transduction.

Why are viroids resistant to nucleases?

Having a circular RNA "genome," they are resistant to most exonucleases (that digest the free ends of RNA or DNA)

Most temperate phages integrate into the host chromosome, whereas some replicate as plasmids. Which kind of relationship do you think would be more likely to maintain the phage in the host cell, and why?

Integration, because plasmids are frequently lost during cell division, which could leave a daughter cell without the virus genome

Which of the following describes a latent viral infection?

Long periods of time with essentially zero viral replication, punctuated by outbreaks of active replication and disease manifestation. Infected individuals are largely non-infectious between outbreak periods.

After beta phage infects Corynebacterium diphtheriae and integrates its DNA into the host genome, the bacterium is capable of causing the disease diphtheria. Which term best describes this phenomenon?

Lysogenic conversion

Which is a filamentous phage?

M13

T/F Sometimes a piece of bacterial DNA near the specific site of insertion stays attached to the phage DNA, and a piece of phage DNA remains behind.

True

T/F The lambda phage DNA always integrates into the host DNA in the same specific site.

True

Phage that lyses the bacterial host when completing its life cycle.

Virulent phage.

Generalized transduction occurs when

a bacteriophage packages a piece of bacterial DNA during replication.

During maturation or formation of phage particles

a few phage heads may surround fragments of host bacterial DNA.

The site at which a virus has infected and subsequently lysed the infected cell, releasing its progeny to infect and lyse surrounding cells, thereby forming a "clear zone," is

a plaque

In a quantal assay, animal viruses are quantified by

administering several dilutions of a virus preparation to a number of animals, cells, or chick embryos, then determining the dilution that infected/killed 50% of the group.

The basic parts of a bacteriophage are

an isohedral head, tail, tail pins, and fibers.

The correct order for the stages of phage infection is

attachment, penetration, transcription, replication of nucleic acid and protein, assembly, release

T/F Generalized transduction is so called because specific bacterial genes are transferred during this process.

False

There are ___ major families of RNA containing viruses that infect vertebrates.

14

In the case of T-even phages, the burst size is about

200 per host cell

There are ___ major families of DNA containing viruses that infect vertebrates.

7

Immunity to superinfection (infection of a cell at a later time with a second, identical bacteriophage) is a consequence of lysogeny. Why does this occur?

A repressor produced by the first virus will actively suppress the lytic cycle of the second virus.

Infection in which a virus multiplies rapidly and spreads in the host.

Acute infection.

Why is it virtually impossible to eradicate a disease caused by a zoonotic virus? -You'd have to drive the vector organism extinct to do so. -Many vector organisms have multiple stages of their life cycle that can carry a zoonotic virus, which complicates controlling the vector-borne transmission. -Many viruses transmitted in this manner may utilize more than one vector organism. -Many zoonotic viruses may be able to reside in more than one host organism, complicating control measures.

All of the above are correct

Once inside the host cell, phage DNA -is replicated. -is transcribed. -may get degraded by bacterial nucleases. -may integrate into the host chromosome.

All of the choices are correct

Which statement about most phages that contain single-stranded DNA is NOT true? -They are extruded from the host cell. -They contain a negative-sense DNA strand. -Their DNA is transformed to dsDNA before replication and transcription occur.

All of the choices are correct

Which of the following descriptions fits a chronic viral infection?

Characterized by continuous production of low levels of viral particles, potentially even in the absence of active symptoms of disease. The organism is usually still highly infectious during this time.

T/F Generalized transduction involves the transfer of phage genes from one bacterial cell to another.

False

Attachment

Phage attaches to specific receptors

Assemby

Phage components are assembled into mature virion particles

Synthesis

Phage genome is transcribed, proteins are translated. Phage DNA is replicated

Transduction resulting from an error in excision of a prophage.

Specialized transduction.

One of the most intensively studied virulent phages which infects E. coli is ______.

T4

Phage that is able to incorporate its genome into the host chromosome.

Temperate phage.

Genome Entry

The tail contracts, DNA is injected into the bacterial cell

Which of the following is not a characteristic of normal cells?

They grow as multiple layers