Virology Flashcards
How are viruses cultured? 3 ways
Primary cell culture from animal tissue
Diploid cell strains is one type of cell that can divid 100x before dying (used to prepare vaccines)
Continuous cell lines are a single cell type that can be propagated indefinitely
What are cytopathic effects?
Changes that virus makes to a cell culture
Includes rounding up, detachment from culture dish, formation of syncytium (group of fused cells)
How do you measure the concentration of a virus?
Plaque assay:
(1) prep a plate dilution on susceptible cells
(2) after the cells attach, overaly them with a semi-solid medium to restrict diffusion of virus particles
(3) now the cells are restricted, so they are stuck as a monolayer visible as “plaques”
(4) use a dilution factor to count the plaques
What is the lowest energy conformation of a virus particle?
Their minimum free energy conformation is attained when an unfavorable barrier is surmounted, following induction of the irreversible conformational transitions associated with attachment and entry
What shapes can the protein coat of the virus be?
Helical
Icosahedral (20 faces of equilateral triangles)
Both are symmetrical shapes
What can envelop some viruses?
What can be embedded in this envelope?
A membrane, which comes from the host cell’s membrane
Sometimes there are viral glycoproteins embedded in the lipid bilayer – these have external binding sites, antigenic determinants, sequences that mediate fusion with cell membranes for entry; internal parts are often essential for virus entry i.e. HA protein of influenza A virus
What are the 7 categories of viral genomes?
dsDNA
gapped dsDNA
ssDNA
dsRNA
ss+RNA
ss-RNA
ss+RNA with DNA intermediate

What is the final piece of genetic info that’s translated to proteins?
+ strand of RNA
Where do viruses enter in the body?
Usually the apical surface of epithelial or endothelial cells
Happens especially if tight junctions are loosened
Once a virus has entered apical surface of cell, how can it spread?
(1) Laterally, causing localized infection of epithelial/endothelial cells
(2) Tranported to basolateral surface to be released to underlying cells & tissues causing a systemic spread
A virion does not infect every cell it incounters.
What determines whether a virion infects a given cell?
A cell must be both susceptible (have the specific receptor which a virion recognizes) and permissive (have the intracellular compartments necessary for replication of a particular virus)
How does dsDNA get converted to +RNA?
mRNA is produced by copying the genome by host or viral DNA-dependent RNA polymerase
How is gapped DNA converted to mRNA?
(1) gaps must be filled to produce perfect duplexes
(2) mRNA synthesis occurs usually by a virus-encoded reverse transcriptase homologous to that of the retrovirus
How is ssDNA converted to +mRNA?
must be converted to a dsDNA template before being made into mRNA (even if the ssDNA is a - strand!!!
ssDNA –> dsDNA –> mRNA
How is dsRNA made into +mRNA?
The - strand of this double stranded RNA is converted to +mRNA by a viral RNA-dependent RNA polymerase to produce viral proteins
How is +strand RNA that’s part of viral genome prepared to “the” +mRNA?
The genome is replicated into a full length - strand
This - strand is replicated into full length + strand genomes
How is a + strand RNA with DNA intermediate prepared to became “the” + strand RNA?
A reverse transcriptase (RNA-dependent DNA polymerase)
The DNA serves as the template for viral mRNA and genome RNA synthesis by cellular enzymes
How is - strand RNA prepared to be the + strand RNA?
virus-encoded RNA-dependent RNA polymerases produce mRNAs from the - strand genome
Which step do the antiviral medications amantadine/rimantadine target?
the uncoating step: when the virus does endocytosis to get into the cell, it has to uncoat (aka lose the membrane around it)
How are viruses assembled?
Make a new genome, new caspid proteins, sometimes even envelope proteins– all occurs in different cellular compartments, so homing signals are required to make sure they get to the right location
Concerted assembly (genome/protein components happen at the same time) or sequential assembly (genome can insert into preformed protein envelope) can occur
How are virus particles released?
Lysis (cell bursts) or cell to cell spread (occurs without physical release of the particle)
How do NA inhibitors work?
i.e. Tamiflu, Relenza
They are neuroaminidase inhibitors (an enzyme that acts upon sialic acid, which is found on glycoproteins on the surface of normal host cells)
Blocking this enzyme prevents new viral particles from being released by infected cells
Where do many viruses enter the body?
Mucosa of respiratory tract, GI tract, UG tract
Outer surface of eye
Skin
What features of the respiratory tract protect it from viral entry?
How do viruses get it?
Swallowing, mucociliary blanket, macrophages in alveoli, IgA
Viruses can be found in aerosolized droplets from when somebody sneezes/coughs
These must be swept away by mucus, neutralized by antibody, or destroyed by alveolar macrophages