Viral Replication Flashcards
Most DNA viruses replicate in the ________, most RNA viruses replicate in the _______
Cell nucleus; cytoplasm
What 2 DNA viruses replicate in the cytoplasm?
- poxviridae
- African swine fever
What RNA viruses replicate in the nucleus?
- orthomyxoviridae
- retroviridae
- some paramyxoviruses (canine distemper)
Replication cycle outline
- attachment or adsorption
- penetration or uptake
- uncoating
- synthesis of viral nucleic acid and protein
- assembly/ maturation
- release
Attachment/adsorption
Virus attaches to cell surface
- occurs via ionic interactions (temp independent)
- recognizes specific receptors on cell surface –> cells without receptors are not susceptible to the virus!
Penetration
Virus enters the cells
What are 2 ways enveloped viruses can enter cells?
- fusion: entry via fusing with plasma membrane
- endocytosis: entry by endosomes at the cell surface
- -> virus taken up by invagination of clathrin-coated pits into endosomes
Endocytosis
Endosome becomes acidified –> virus membrane fuses with endosome membrane
- fusion of endosome and viral membrane = release of internal components of virus
Penetration for non-enveloped viruses
Virus crosses plasma membrane directly, or is taken up via clathrin-coated pits into endosomes
- virus directly crosses endosome membrane
Uncoating
Nucleic acid must be uncoated before virus replication can begin
- after uncoating, infectious virus particles cannot be recovered from cell (lasts until new infectious virions are made)
Assembly/maturation
Maturation may follow the initial assembly process
- viruses in final stage of assembly go thru a set of structural transitions and/or biochemical modifications that transform recursor particles into infectious particles
Release
- cell lysis
- budding (does not have to kill host cell)
- not all released viral particles are infectious
- enveloped viruses released by budding from plasma membrane
Structural protein
All proteins in a mature virus particles, even if they make no contribution to the morphology or rigidity of the virion
Non structural protein
Viral proteins found in the cell, but not packaged into the virion
How do viruses affect host cells?
Many inhibit host RNA, DNA or protein synthesis
- damage the function of cells or kills cells
Cytopathic effect
Morphological changes in the host cell caused by viruses
- consist of cell rounding, disorientation, swelling/shrinking, death, detachment from the surface
- depends on virus and cells on which it is grown
- will take a couple of inoculations to see CPE on artificial media
Use of CPE
- identify virus isolate
- quantitate infectious virus particles by the plaque-forming unit
Isolation and propagation of viruses
- animals
- embryos
- cell cultures
The more virus passes or adapts in host cells, the more _______
Virulence the virus becomes to the host
Preparation of specimen for inoculation
Fresh or frozen tissues –> homogenize –> freeze and thaw (rupture cell/release virus) –> low speed centriguation and filtration –> spin down viruses with ultra speed centrifugation
Primary culture
First in vitro cultures of cells taken directly from the organs
- requires death of animal hosts
Cell line
Cell line that can be subcultured and grow continuously
- ex: tumor cell that can be subcultured for many passages
- do not need to kill host
Growth of virus in cultured
- choice of cultured cells
- recognition of viral growth
- growth of virus in lab animals
- growth of virus in embryos-chicken embryonic eggs
A virus contains DNA and RNA
False
Viruses must have either double-stranded DNA or RNA
False
All viruses have an envelope
False
Viruses can be propagated in rich artificial media without cells
False
- cannot make proteins on their own
Adenoviridae
- site of replication: nucleus
- eclipse period (hr): 10
- budding (membrane): none
Herpesviridae
- site of replication: nucleus
- eclipse period (hr): 4
- budding (membrane): nuclear
Poxviridae
- site of replication: cytoplasm
- eclipse period (hr): 4
- budding (membrane): golgi
Retroviridae
- site of replication: nucleus
- eclipse period (hr): 10
- budding (membrane): plasma
Only enveloped viruses can do _______, but both enveloped and nonenveloped viruses can do _________
Fusion; endocytosis
Are all progeny created from replication infectious?
NO
- could be noninfectious due to mutations, etc
You do not know if a virus is present within a cell without ______
CPE
- each virus has its own unique CPE
