CBG Lecture 20: Viral diversity Flashcards
define virus
a small non cellular agent consisting largely of nucleic acid within protein coat and requiring a cell for reproduction`
what is a way in which viruses differ from eachother
genome diversity ss or ds DNA or RNA circular or linear \+ sense or -sense segmented or nonsegm life cycles replication strategy
name some DNA viruses
herpes
pox
mimi
name some rna viruse
picorna
polio
rubella
HIV
is herpes virus dna/rna
dna
is polio dna/rna virus
rna
is mimivirus dna or rna virus
dna
what is max size of rna virus
30kbp
what is range of dna virus
3-800kb
which viruses tend to have overlapping genes
those with small genomes
is HIV rna or dna virus
rna
what is HIV genome size
9kb
how many strands are most rna viruses
single stranded
which RNa viruses are double stranded
reoviruses
what is unusual about reoviruses
they are RNA double stranded
what ssDNA viruses are there
some small viruses
whats unusual about parvoviruses
v. small SINGLE stranded dna virus
name a circular dsDNA virus
SV40
what is unusual about SV40 virus
has circular dsDNA genome
which viruses have lower error/mutation rate
dna viruses, because DNAP has proofreading arm
what is the effect of RNA viruses having a high mutation rate
every RNA virus is different so get quasispecies
what is a quasispecies
virus doesnt exist as single sequence but pool of sequences making it v difficult to make vaccines
why is it important for big viruses to be dsDNA
more stable therefore lower mutation rates
how can RNa viruses have genome that is mostly ss but with some ds
because can make ds by looping structures - secondary structures eg. hairpin
in what direction does - sense viruses go
3’ 5’
how do -sense viruses replicate
produce +sense mRNA before production of viral proteins
input RNA then to +RNA then to progeny RNA then to virions which are -sense 3’5’
what are polarity switches
from virion of -sense RNa back to +sense RNA
give example of segmented virus
influenza
give example of non-segment
retrovirus
give example of +sense non-segmented genome
retrovirus
what genome do retroviruses have
+sense non-segmented genome
how do nonsegmented viruses evolve
mutation
recombination
how do segmented viruses evolve
mutation
recombination
assortment
how many segments in influenza virus
7/8
when does antigenic shift occur
when RNA segment are exchnaged between viral strains in a secondary host
no cross protective immunity to virus expressing a novel hemaglutinin
what microscope used to see viruses
EM
what is basic structure of a virus
genome (nucleic acid) surrounded by capsid eg.TMV
give example of virus which has genome surrounded by capsid
TMV
what does the capsid of a virus do
protect nucleic acid
how can virus capsid be assembled
self assembly - monomeric protein units produce spherical particles
one or more capsid prteins:icosahedral formations
name some ds segmented RNA virus
reoviridae
name some nonsegmented negative strand rna virus
paramyxoviridae
filoviridae
name a segmented - rna virus
orthomyxoviridae
bunyaviridae
name a virus with an envelope
retrovirus: hiv
name some dna virus
circo/parvo/papoadeno/herpes/pox
name some host specific viruses
small pox and polio are human specific
name some human specific viruses
smallpox and polio
what is mortality rate of ebola
90%
for most viruses, how many viral cells do you need to get exposure to to contract it?
whyh is ebola the exception
normally need 1000s virus eg.polio but with ebola need 1
define zoonotic
infectious diseases of vertebrates that can be naturally transmitted to humans eg.rabies
name a zoonotic virus
rabies
ebola
what is WNV
west nile virus
how is WNV transmitted
crow to crow transmission in caged birds by infected mosquitos
what is WNV vector
mosquitos
how do mosquitos become infected with WNV
when they bite birds infected with WNV
what are the dead end carriers of WNV
uhans - the virus is not sufficient to be transmitted back to the mosquito, thereby ending transmission cycle
why are humans dead end csarriers of WNV
because the virusin them is not sufficient enough to be transmitted ack to mosquto therefore ends the transmittion cycle
whats unusual about mimivirus
physically big and related to other dsDNA viruses
how many genes do mimiviruses contain
what is its genome size
900
1Mbp genome size
apart from mimivirus, what virus has next biggest genome size
poxvirus
how many genes does poxvirus contain
900
how can you eradicate a virs
need to be human specific, effective vaccine, need virus to produce symptoms, need antigenetically STABLE virus
name some asymptomatic viruses
WNV in some mamals
poliovirus
how old are RNA viruses
up to 3.5bn yrs old
what are similarities between HIV types 1&2
replicate in the nucleus
contain 2 env proteins
contain RT
envelope fuses with cell membrane
how does adenovirus getinto host cell
endoctosed
how does influenza get into host cell
endocytosed then fuses with the endosome in a pH dependent manner
