lecture 2- viral replication Flashcards
what is a virion?
extracellular or intracellular infectious form of a virus
what are the 6 basic steps of viral infection/replicaiton
- viral attachment
- endocytosis
- uncoating
- replication
- assembly
- egress
eclipse period
the period between the entry of the virus genetic material into the host, causing infection and the appearance of new mature virus in a host cell
latent period
before virus is released
tissue tropism depends on … (2)
- susceptibility (suitable receptors on host)
- permissivity (host cellular machinery must be able to support viral replication and release)
how do enveloped viruses enter a cell
virus attaches to host plasma membrane at receptor sites with glycoproteins then envelope is lost during endocytosis (uncoated) and only nucleus and capsid enters the cell
how do naked viruses enter a cell (2 mechanisms)
whole virus enters in a vesicle made from host plasma membrane (ex: adenoviruses)
OR
only genome enters via pore-mediated penetration (ex: picornaviruses)
which of the following steps is used by all viruses?
translation
transcription
RNA rep
DNA rep
reverse transcription
translation
why doesnt pox virus replicate in the nucleus, despite being a DNA virus?
poxvirus has its own transcriptase and thus does not need to replicate in nucleus
where do most DNA viruses replicate? why?
most replicate in host nucleus because they need cellular polymerase and RNA polymerase 2
where do most RNA viruses replicate? why?
most RNA viruses replicate in host cytoplasm because
a) +vs sense viruses can act as mRNA
and
b) -ve sense viruses carry RNA dependent RNA polymerase
what are the exceptions to RNA viruses replicating in cytoplasm?
retroviruses replicate in nucleus and cytoplasm
influenza replicates in nucleus
hepadnavirus replicates in nucleus and cytoplasm
replication strat of dsDNA
host cell Pol (except pox)
replication strat of ssDNA
host cell Pol –> dsDNA intermediate
replication strat of dsRNA
do not depend on host Pol–> carry viral RNA pol
replication strat of +ve ssRNA
directly access host ribosome
replication strat of -ve ssRNA
carry viral pol (RdRp) –> +ve ssRNA intermediate
replication strat of ssRNA (retro)
DNA intermediate –> integration into host genome (carry reverse transcriptase and integrase)
true or false: herpesvirus is very highly regulated
true
what differentiates the replication style of herpesvirus
- very highly regulated
- alpha, beta and gamma regulatory proteins (cascade, starting with alpha)
- DNA virus –> replication occurs in nucleus
what differentiates the replication style of flavivirus?
- RNA viral rep (replication occurs in cytoplasm)
- less regulated
- +ve sense RNA
- creation of polyproteins
-envelopment by plasma membrane
what 2 enzymes are needed for retrovirus replication
reverse transcriptase and intergrase
what role does intergrase have in retrovirus replication
integrates viral genome into host genome in host nucleus
lysis of the host cell more commonly occurs with a) enveloped or b) naked viruses?
b) naked viruses
usually accumulate in nucleus or cytoplasm and release by lysis of host cells, vs enveloped which bud off of plasma membrane
examples of enveloped viruses
herpes, pox
examples of naked viruses
adeno, picorno, reo, calici
what viruses replicate in both the nucleus and the cytoplasm?
hepadnavirus and retroviruses
when replication occurs in the cytoplasm, what is this called?
reverse transcription
are enveloped viruses infectious before their envelope is acquired?
no
where can enveloped viruses be released/budded off from
mucosal surface
endoplasmic reticulum
cytoplasm
golgi
nucleus
basal surface
can viruses replicate in water?
not without a living host
what is special about poxvirus in regards to viral replication
despite being a DNA virus, it replicates in the cytoplasm
what is special about influenza in regards to viral replication
despite being a RNA virus, it replicates in the nucleus
