Introduction to viruses Flashcards
viruses are obligate
intracelluar parsite
are viruses living
no - inert particles
if virus needs enzyme to replicate its genome, the virus must do what
provide it itself - certain enzymes virus needs for replication and the virus has to carry those in itself
anything needed after stage of mRNA
virus doesn’t need to carry, ti will just happen
virus will self ______ within host cell
assemble
virus particle called
virion
virus has to have
genome
what kind of genome does virus have
DNA or RNA
if DNA genome can be
linear or circular
single or double stranded
RNA genome can be
linear or segmented
single or double stranded
if single stranded rna genome what is important
polarity
what are three possibilities for rna genome for virus
positive sense or negative sense or ambiesense (+ at one end - at one end)
negative sense RNA
opposite to mRNA cannot be directly translated
need enzyme to make RNA
RNA dependent RNA polymerase
all viral genoms have to be associated with what kind of proteins
capsid
what are possible structures for capsid
helical capsid
icosahedral capsid
capsid + nucleic acid is calld
nucleocapsid
what is actually introduced into cytoplasm of cell
nucleocapsid
minimal structure of virus
genome + capsid proteins
some viruses will have add’l structures
envelope
peplomers
packaged enzymes
envelope viruses will have
envelop
what is envelope
part of membrane of cell that the virus affected and assembled in
lipid bilayer that surrounds nucleocapsid
peplomers
viral glycoprotein spikes
targets for neutralizing antibodies
what is important about peplomer
targets for neutralizing antibodies
many viruses are designed to neutralize
peplomer
what does virus use to attach to specific receptor on host cell
peplomer (viruses block attachment!)
if virus needs enzyme the host cell can’t provide ie needs
pakcaged enzyme
what are examples of packaged enzymes
replicases, proteases
viral proteins that make up virion are called
structural proteins
oms proteins made during replication cycle of virus - they don’t become part of virus - they are called
non-structural proteins (not part of virion)
encoded enzymes a virus may need are not always packaged in
virion
ultimately virus needs to get to what stage on its own
mRNA
examples of helical enveloped virus
pox virus
rabies virus
HIV
how are viruses classified into order, family, etc (taxonomic classification)
how they replicate
*polarity/strand of genome
type of disease it will cause
most common route for infectious disease and true for virus
mucousal route (inhalation or ingestion)
once virus enters,once a virus enters,
limited replication then virus spreads
how can virus enter
repiratory, wounds, STD, fecal-oral
when virus enters there can be replication at
initial site it entered
incubation preriod
there can be asymptomatic period or prodrom period
dissemination may occur -
they may spread from primary to secondary site
some viruses spread to what site
tertiary
what is responsible for spreading HIV
dendritic cells
primary site replication can be spread to
secondary site
secondary site replication can be spread to
tertiary site
but not all viruses will spread correct?
yes
4 types of viral infection
abortive
productive - nonlytic
latent
productive - lytic
abortive
cell cannot survive replication of virus or virus itself is defective
productive (non-lytic)
the host cell is altered but not killed- permissive and productive
producive nonlytiic is often viruses that have
envelope
productive - lytic
host cell death and release of progeny viruses
- permissive and productive
cell is lysed during replication
producitve - lytic characteristic of what virus
no envelope
latent viral infection
viral genome persists inside host cell without production of virus particles
latent viruses can become reactivated
when latent viruses are reactivated lead to production of
virus particles
lytic infections mediated by
naked viruses (no evvelope)
budding is mediated by
envloped virus (during budding iti will aquire envelope)
regardless if relase is lytic or budding what are the steps
Adherence Penetration Replication Assembly Release
penetration
release nucleocapsid into cell
replication
synthesis of viral proteins
release
lysis or budding
transofrming virus e cause
cancer
do all transofrming viruses integrate
no
first step due o highly speicif reaction of
peptomer
specificity of peplomer receptor interaction determins
tropism (type of cell virus can affect)
tropism:
(type of cell virus can affect)
permissiveness
allows virus to enter and replciate
two main strains of HIV
T tropic
M tropic
T tropic HIV straing primarlily affects
t lymphocyte
m tropic strain primarlily affects
macrophage
both strains HIV the receptor primarily binds to
CD4
once virus binds to CD4 what happens
it undergoes conformational change that allows it to bind to a coreceptor
coreceptor for m tropic strain of HIV
CCR5 (chemokine receptor)
coreceptor for t trophic strain
CXCR4 (chemokine receptor)
m tropic strain of hiv will not affect
t lymphocytes
t trophic strain of hiv will not affect
macrophage
influenza virus peplomer called
Haemagglutinin
HA stands for
Haemagglutinin
where does human flu replicate
airway epithelia
once it binds has to deliver
nucleocapsid into cell
can enevloped viruses fuse
yes - they can fuse with bilayer of host cell
where does fusion occur
often cell membrane but can be membrane inside cell like endosome
can naked viruses fuse
no b/c they just have coating of protein and own’t fuse with lipid
adenovirus enduses induces
lysis of endosome once its taken up
main mechanisms virus can enter cell - draw out
pg 20
influenza virus will only fuse at
acidic pH
HIV virus will fuse at
neutral pH
neutral pH fusion takes place where
at surface of cell
acidic pH fuses wehre
endosome
fusion at acidic pH is also called
pH dependent fusion
poliovirus will form what in endosome
pore - it allows genome to be available for replication
adenovirus lead to what of endosome
lysis - then the nucleocapsid is delivered to where it replicates
what is function of spike glycoproteins
bind to receptor on surface of cell allowing the cell to become infected (they remain in membrane!)
they define where they are going to bud from cell by the spike glycoproteins
multinucleated giant cells are called
syncytia
influenza viruses taken up into endoxomes and then
it fuses - it needs the pH to drop
will syncytia formation happen during influenza
no
will ther be fusion at neutral pH for influenza virus
no - they cannot force fusion at the neutral pH it needs pH to drop
entry does not necesarilly require
fusion (naked virus!)
naked virus will not fuse with
lipid membrane
once nucleocapsid is delivered and uncoated what needs to happen
need to replicate
enzymes that carry ou replication are
host or viral enzymes (or both)
enzymes always made on host
ribosomes
once repplication happens there will be
assembly & release
naked virus released by
lysis
not naked virus released by
budding
large DNA viruses life cycle
wave of transcription
immediate early genes expressed followed by early genes, they encode proteins that regulate the transcription and replication of virus. they are made early on. many RNA virsuses don’t have wave of transcription, most you just straigt away mke structural/nonstructural proteins
in macromolecule once genome made then
make what is needed to package enome
what are stages of macromolecular syntehssis and replciation
Transcription of Immediate Early and Early mRNA synthesis of nonstructural regulatory proteins
Replication of genome
Transcription of Late mRNA structural protein synthesis
when viruses are assembling they can give rise to
inclusion bodies
inclusion bodies
proteins falling out of solution - so many proteins being made
where will inclusion bodies be
wherever replication is taking places
what is period b/w addition of virus where amount of virus seems to decrease
eclipse period
why does amoutn of virus decrease once injected
b/c it is being taken up into cell
eclipse period
b/w infection and when more virus can be detected than what was added (length depends on virus)
RNA viruses encode
RNA-dependent RNA polymerase
permissivness =?
entry + replication
what are syncytia
multinucleated cells
pH independent fusion leads to the formation of what
syncytia (multinucleated cells)
what are chemokines
chemoattracts that a cells in our body make to tell immune system there is infection going on
HIV fuses with what membrane
plasma
enveloped viruses fuse with what
host cell membrane - often plasma membrane but isn’t always
fusion at neutral ph is also called
ph independent fusion
what is the result of fusion at neutral pH
once nucleocapsid is released into cell, spike glycoproteins remain in the plasma membrane
the spike glycoproteins allows them to fuse with other cells with spike glycoproteins resulting in multinucleated cells
