Virology II Flashcards
replication curve
initial latent period followed by exponential growth
what occurs during the latent period
producing early enzymes, nucleic acids, and protein coat
NO production of infectious virus from cells
when during the replication curve are structural components of the virus produced
end of replication curve –> exponential growth
what are the steps of the replication cycle
- attachment
- entry
- uncoating
- replication
- assembly
- release
replication cycle for an enveloped DNA virus
- virus envelope binds to receptors on host cell
- envelope fuses w/ plasma membrane so only encapsidated virus enters
- viral genome (DNA) exits from the capsid and enters the nucleus via a nuclear pore than circularizes inside the nucleus
- transcription and translation of early proteins produces transcription factors that promote synthesis of late proteins; late proteins encode the capsid and envelope
- genome gets enclosed into the capsid at the inner leaflet of the nuclear membrane
- assembled virus buds off of the nuclear membrane to form a vesicle; vesicle fuses with outer cell membrane to exocytose out of the cell in a lipid envelope
how do antiviral drugs work
target any stage of the replication cycle
- helicase/primase inhibitors
- nucleoside analogs
- protease inhibitors
replication cycle for an enveloped RNA virus
- virus envelope binds to receptors on host cell
- entire virus gets engulfed into the cell –> forms endosome –> drop in pH triggers fusion of viral envelope with endosome membrane
- viral genome (RNA) exits from the capsid and enters the cytoplasm
- RNA viral genome acts as a template for complementary RNA strands via RNA polymerase –> new copies of viral genome are made
- comp. RNA strands also act as mRNA –> gets translated into capsid proteins in the cytoplasm and envelope glycoproteins in ER/golgi - capsid assembles around each new copy of the viral genome in cytoplasm; vesicles transport the envelope glycoproteins from golgi then fuse with outer cell membrane to present glycoproteins on cell surface
- capsidated virus buds off of the outer membrane, forming the envelope surrounded by glycoproteins
attachment
interactions between virus and cell surface proteins/carbohydrates
how do viruses find host cells
viruses are free floating - must encounter host cells that express the correct receptors
what determines specificity of virus binding to host cells
host cells must express the correct receptors in order to be infected by viruses
receptors determine tropism for certain tissues within certain hosts
adhesion vs entry receptors
adhesion: initial binding between virus envelope and host cell; loose adhesion
entry: final binding between virus envelope and host cells; tight adhesion
entry and uncoating
breaching the plasma membrane and releasing the genome
mechanisms of entry and uncoating
- direct penetration
- membrane fusion
- endocytosis
direct penetration
capsid does not enter the cell
injects viral genome directly into the cell
membrane fusion
envelope attaches and fuses to release capsid into cytoplasm
endocytosis
entire envelope and capsid gets engulfed into the cell
many different pathways exist
replication
producing more viral genomes
STRATEGY: depends on viral genomic acid and its polarity
LOCATION: depends on genomic nucleic acids (DNA vs RNA)
where do DNA viruses replicate
nucleus
where do RNA viruses replicate
cytoplasm
positive sense RNA replication
looks like mRNA –> can be directly translated into viral proteins
does not require virus to have its own RNA polymerase
negative sense RNA replication
opposite direction than mRNA –> must be transcribed by RNA polymerase into a positive sense strand before translation can occur
virus must have its own RNA polymerase attached
assembly and release
newly synthesized genomes assemble into new viruses and get released
where do DNA vs RNA viruses assemble and release
DNA: nucleus
RNA: cytoplasm
how are enveloped viruses released
budding off of the cell - takes components of the outer cell membrane with it to form envelope
can occur on different sides of the cell to allow for systemic spread or viral secretions
how are encapsidated viruses released
lysis of the cell
can not bud off because does not have an envelope made of membrane components
physical viral assays
measure the presence of virus structure, antigen, or genome
- hemagglutination assay
- hemagglutination inhibition
- ELISA
- PCR
hemagglutination assay
determines presence of viral antigen
combine sample + RBCs in a well
- if antigen present –> virus will agglutinate the RBCs together to make solution diffusely pink
- if no antigen present –> lack of virus will cause RBCs to clump and sink to the bottom
hemagglutination inhibition
determines presence of viral antibody
combine virus + RBCs + sample in a well
- if antibody present –> will bind virus and prevent agglutination causing RBCs to clump and sink to the bottom
- if no antibody present –> virus will agglutinate and well becomes diffuse pink
ELISA
determines presence of viral antigen
sample + known antibody to see if antibody binds to antigen in sample
sandwich method vs non sandwich
PCR
determines presence of viral nucleic acid
replication of viral genome within patient sample
early fluorescence indicates higher concentration of viral genome in the sample
biological viral assays
measures how infectious the virus is
- culture and cytopathic effects
- plaque assays
culture and cytopathic effects
determines if a virus is infectious
inoculating virus within the cell line and determining the reaction
plaque assay
determines how much infectious virus there is
measures plaque forming units per volume of sample tested
