Ch 13

Most phages that contain single-stranded DNA

***ALL***

Please select the three methods that are used to cultivate animal viruses.

***ALL***

Spongiform encephalopathy occurs in

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Animal viruses are divided into a number of families whose names end in

-viridae.

Please order the following steps to reflect the order in which they occur in the replication cycle of an animal virus.

1 - Adsorption (attachment) to host cell surface 2 - Penetration and uncoating 3 - Synthesis of viral nucleic acid and proteins 4 - Assembly of viral particle 5 - Release from host cell

What is a defective phage?

A virus that has lost some of its genetic material, and therefore cannot replicate within a new target cell.

The term filterable viruses was coined by

Beijerinck.

Infective and non-infective viruses may be distinguished by growth on MacConkey's agar.

False

Why are viroids resistant to nucleases?

Having a circular RNA 'genome,' they are resistant to the digestion of most exonucleases (that nibble/digest the free ends of RNA or DNA).

Would ID50 and LD50 necessarily be the same for a given virus? Why or why not?

No, because a virus may be highly infectious (very low ID50 value) but only marginally lethal (very high LD50 value). A prime example of this is the rhinovirus (common cold virus).

Would you expect the number of virions to be the same if you measured them by the plaque assay or by counting using the electron microscope? Why?

No-the plaque assay only measures viable virus particles, while the electron microscope cannot distinguish between defective and viable virus.

The family to which the Rhinovirus belongs is the

Picornaviridae.

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

Spikes.

Crystallization of Tobacco Mosaic Virus was accomplished by

Stanley.

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

T4.

Why is it that abnormal forms of prion self-proteins can accumulate over time in the central nervous system, leading to disease?

The abnormal forms are resistant to normal cellular protease degradation.

If a virus utilizes a lytic life cycle of reproduction, it will not induce tumors.

True

Virulent as well as temperate phages can serve as generalized transducing phages.

True

Viruses that cause acute infection result in productive infections.

True

A consequence of lysogeny is lysogenic conversion. What does this term mean?

When a bacterial cell starts to produce a new phage protein (e.g. diphtheria toxin) after the viral genome inserts into the host genome.

Lysogenized cells

are immune to infection by the same virus AND may have new properties.

Prions

are made of protein only.

Which does not refer to the shape of a virus?

bacillus

The shape of the virus is determined by its

capsid.

Once integrated, phage DNA can remain in the prophage state as long as

certain phage genes are repressed.

A virion is a(n)

complete, extracellular virus particle.

If the infecting phage lacks some critical pieces of DNA necessary for replication it is called

defective.

Viruses are commonly referred to by their _________ name.

disease AND species

The common species name of the virus is based on the

disease the virus causes.

The viral envelope closely resembles the

eukaryotic cell membrane.

What are two ways that phage can replicate in harmony (not directly lysing) their host cell?

extrusion and lysogeny

The receptors to which animal virus attachment proteins usually bind are

glycoproteins.

The best known chronic infection involves

hepatitis B.

The best-known examples of viruses that cause latent infections are

herpes AND chickenpox.

Specialized transduction

involves the transfer of a few specific genes, utilizes a defective virus AND only involves genes near the viral DNA integration site.

The phenomenon responsible for the ability of Corynebacterium diphtherium to produce the virulent toxin responsible for the devastating effects of diphtheria is called

lysogenic conversion.

Cells taken from a tumor

may be used to grow viruses AND can be cultivated in vitro indefinitely.

Filamentous phage

only infect E. coli that have pili.

In latent infections, the virions are

only produced during reactivation.

A limiting factor for viral infection is

presence of specific receptor molecules on the host cell.

Normal tissue taken from animals and prepared immediately as media for viral growth is termed a(n)

primary culture

The approximate viral concentration of a sample may be determined by

quantal assay.

The terms isometric, icosahedral and pleomorphic refer to

shapes of viruses.

In the region of budding, the plasma membrane becomes involved with

spike proteins AND matrix proteins.

The genome of retroviruses is made of

ssRNA.

In the replication of phage containing positive-sense DNA,

the host's enzymes are used to make dsDNA.

Retroviruses are unique in that they

use RNA as a template to make DNA.

A phage that replicates inside the host cell and then lyses its host during its release is a

virulent or lytic phage.