Virology

Viruses contain either ______ or ______ as their nucleic acid

DNA or RNA

T/F: Viruses utilize both DNA and RNA as the template for transcription

True

The nucleic acids of viral genomes are usually linear except __________ and ________ which are ________-

circoviridaie and papillomaviridae which are circular

viral genomes are either ______ or ______

segmented or nonsegmented

The only viruses with segmented genomes are:

Bimaviridae
Bunyaviridae
Orthomyxoviridae
Reoviridae

A Theory of virus evolution:
Viruses originated from primitive, pre-cellular ________ replicons

Primitive pre-cellular RNA replicons

viruses originated from segments of cellular ____ ______ which acquired the ability to replicate

nucleic acid

Free living organisms lost their genetic information and became dependent on other cells.

The Regressive Theory

Viruses __________ with their host cells

co-evolved

What are the two types of viral symmetry?

Icosahedral
Helical

All _______ and most ______viruses are Icosahedral, except ________

Poxiviridae

The only helical symmetry viruses are: (5)

Bunyaviridae
Coronaviridae
Orthomyxoviridae
Paramyxoviridae
Rhabdoviridae

What 5 parts make up a virus structure

Capsid
Envelope
Envelope Glycoprotein
Peplomers (peplomers)
Matrix Proteins (tegument)

T/F there is a single/unique prperty essential for species delineations

FALSE there is NO single or unique property

What are the 4 components of species delineation?

1. Type/Nature of the Genome
2. Mode/Site of replication
3.Structure of the virion
4.Sequencing of the viral genomeh

________ occurs when virions are not detectable

Eclipse phase

Fully assembled virions are released from infected cells by _______ or ______

Budding or cytolysis

What is the first step in viral replication

attachment to surface receptor on a host cell

what is the second step of viral replication

entry into the cell

what is the third step of viral replication

uncoating of nucleic acid

what is the 4th step of viral replication

replication of viral nucleic acid and synthesis of virus encoded protein

what is the 5th step of viral replication

assembly of newly formed virus particles and release from host cell

what are the 3 mechanisms NON-ENVELOPED viruses enter the cytosol?

1. introduction of viral genome via channels or pores
2. perforation- entire virus enters without lysis of the membranes
3. virus lysis and is released from endosome via acid-activated rupture

Uncoating is done by enveloped or non-enveloped viruses?

Both

What is uncoating?

the viral genome is released in the cell (parial or full dis`assembly of the virus)

Production of _____ is required for synthesis of viral proteins.

mRNA

DNA viruses which replicate in the nucleus use host cell _______to synthesize _____

transcriptases, mRNA

RNA viruses use ________ as mRNA OR make _________ to create mRNA

the viral genome (RNA), RdRp (RNA-dependent RNA polymerase)

RNA viruses replicate in the ________

Cytoplasm

What are inclusion bodies

viral inclusions in host cells visible under the microscope.

______ replicates in the nucleus but its inclusion bodies are in hte cytoplasm

circovirus

Two examples of single stranded DNA viruses are: hint: they must infect replicating cells, so that they can become ds DNA

Parvovirus
Circovirus

Retroviruses make _______ from their RNA using what enzyme NOT made by the host cel

ss DNA, using RNA dependent RNA polymerase

Retroviruses use ________ to create ds DNA from ssDNA, and input the virus into the host cell genome.

intgrase

What is ambisense

a mixture of positive (5-->3) and negative (3-->5) genome directions

_______ creates mRNA fron ds DNA

transcriptase

ss DNA ---------> ds DNA via:

DNA- dependent DNA polymerase

What two enzyme are in retroviruses to support replication?

reverse transcriptase and integrase

Non-enveloped viruses are released following __________

cell lysis

Two ENVELOPED viruses that are cytolytic are:

togaviruses
paramyxoviruses

T/F a virus that kills the cell is NOT more pathogenic than a virus that does not kill the cell

TRUE

What is a conditional-lethal mutant:

a virus that can only grow in a particular condition. example: temperature

What are antibody-escape mutants

the mutation can grow in an animal that was previously immune.

What are defective-interfering mutants?

a mutation occurred that cut out a piece of virus genome. This shorter portion is replicated. The short piece is NOT capable o infection.

T/F: If a defective interfering mutant is present the then the normal viral genome will be replicated and not the DIM

False, DIM's are replicated.

What is a host-range mutant

a virus mutant that can affect something other than the host species.

When a virus is passed through a non-host species multiple times it becomes host species________ and will ______ to the new species

Attenuated to the host
Adapt to the new species

What are antibody escape mutants?

the virus is not recognized by an antibody. (influenza)

A defective interfering particles require a _______ for replication

the original virus

The exchange or transfer of genetic material between different viruses in the same cell is ________

genetic recombination

genetic recombination can occur between viruses, and between viruses and the _______

host cell

What are the three types of genetic recombination

1. intramolecular
2. copy choice
3. reassortment

Genetic ______ may result due to recombination

reactivation

Intramolecular recombination occurs in _____ Viruses

DNA

Dissociation and reestablishment of covalent bonds describes ________ recombination

intramolecular

Copy choice recombination is seen in what virus types

positive- sense- single - stranded RNA viruses

During copy choice recombination _______ switches between RNA strands during synthesis of the new RNA

RNA polymerase

What virus does copy choice recombination occur frequently in?

coronaviruses (has a large ssRNA)

________ occurs randomly with segmented genomes such as with these three viruses.

Reassortment,
orthomyxoviruses
reoviruses
bunyaviruses

what is reassortment

various segments of genomes are mixed in cells that are infected with multiple viruses.

Reassortment results in a rapid ____ ______

antigenic shift

in _________ _________, a cell is infected with multiple viruses, infectious progeny are produced from both parental viruses. the parental viruses may or may not be infectious.

Genetic reactivation

T/F genetic reactivation may be caused by intramolecular recombination, copy-choice recombination or reassortment.

True

T/F In genetic recombination the parent and progeny viruses are the same.

False

T/F Complementation and phenotypic mixing does NOT result in a change of the genome

TRUE

what is complementation?

Two viruses are on one cell. Once virus has a defective gene, the other has a functional gene. The functional gene product is substituted for the defective gene product. These viruses do not have to be related

What is the term for a defective virus

A satellite virus.

Describe phenotypic mixing

NO defective virus. The progeny of one viruses is released from the cell and is surrounded by the envelope containing glycoproteins that were made by the other virus

T/F The parent virus of the satellite virus must be there for the satellite virus to cause disease

True

T/F Satellie viruses can replicate and grow in culture

False

T/F Defective Interfering Particles can cause disease only with the parent virus.

FALSE defective interfering particles can cause disease with the parent and with other families of virions.

T/F Reassortment must include the genome

True

T/F phenotypic mixing involves the genome

False, phenotypic mixing only involves the envelope.

What are inclusion bodies created from?

viral nucleic acid, viral protein, or altered cellular material.

where are inclusion bodies located?

in the cytoplasm or the nucleus

What are negri bodies

inclusion bodies due to rabies.

Intracytoplasmic Inclusion bodies are made by what 4 viruses

poxvirus
reivirus
rabies virus
paramyxovirus

What 3 viruses cause intranuclear inclusion bodies

adenoviruses
herpesviruses
parvoviruses

What viruses causes both intranuclear and cytoplasmic inclusion bodies

canine distemper virus

Which viruses induce cell fusion

lentiviruses
paramyxoviruses
herpesviruses

fused cells are called what

syncitia
(the viruses are syncytial viruses)

What is hemadsorption

the binding of red blood cells to the surface of infected cells

What three viruses cause hemadsorption

orthomyxociruses
paramyxoviruses
togaviruses

What is hemagglutination

clumping of red blood cells when they are mixed with free virions.

T/F only enveloped viruses cause hemagglutination

Fales: both enveloped and non-enveloped viruses cause hemagglutination

What types of tests are used to detect and identify specific viral species

Serological tests

What color do cells infected with a virus stain with immunoperoxidase

red

What is Pathogenicity

the ability of an organism to infect a host and cause disease

what is infectivity

the ability to invade and replicate. It does not mean the virus is pathogenic

How do you calculate pathogenicity

Pathogpathogenicity = infectivity x virulence