lecture8 Flashcards
(24 cards)
what kind of genome does COVID have?
+RNA genome
helical nucleocapsid
non segmented
how might a virion acquire phenotypic properties that differ from what is encoded in its genome?
if co infected by 2 allelicily different viruses—> each can encode progeny genomes & proteins that can assemble in random mixes
what does SARs encode that affects ___ response?
delayed IFN1 signaling
what is the features of Flu A?
kind of virus?
category?
ortho
- RNA virus–> helical nucleocapsids
Segmented & enveloped
RdRP
- has HA and NA
-8 genome segments
factors that influence virus variability:
replication via macromolecular assembly allows molecular sampling
how does this work?
–genotype mixing
phenotype mixes—>protein mosaics, 1 gen, a mix of both (broader tropism)
second generation–> inherence affects genome
factors that influence virus variability:
virus mutatation rates are much higher than cells
how?
- use own polymerase’s—> RdRP or RT
–usually lack proofreading (except corona but not perfect)
–RNA harder to read than DNA–> more error prone
–DNA virus uses host
some viruses accumulate about _____ mutation per genome per ____ cycle, meaning _____
one mutation
replicate cycle
no two viral genomes are alike
factors influence virus variability:
high fecundity of virus produces large pools of mutants from which variants with selective adv. can emerge
what are quasispecies?
drug resistance?
quasispecies—> pool of genetic variability that may include members with greater fitness in a new environment
defective lineages who can’t survive die off & disappear
lineages who can fight the drug expand and dominate
factors that influence virus variability:
reassortment and recombination
how?
what is antigenic drift?
reassortment–> genotype mixing , requires co infection on the organism and on the cell level
reassortment results in genetic (antigenic) shift
-resutls from virus mutations but is observed by the host —> each years epidemic is from antigenic drift
how does antigenic drift work on the flu?
well what’s antigenic shift?
minor changes in HA or NA surface antigens
-results in entirely new allele
what is an epitope?
region of molecule that elicits an immune response–> antigenic determinant
how could H1N1 flu reemerge in 2009?
why?
pigs are infected by flu A—–> but genetic drift is not common
pigs live less than a year, so animals do not maintain immune memory of previous infections
can flu go under antigenic shift?
why are so many ppl infected?
—-no—> has lots of genetic variation because it can’t undergo antigenic shift ( new allele), but can drift to make little variations
–more than 100 types due to antigenic drift
why are retrovirus recombination prone?
how does coronavirus show this?
co packaged with 2 RNA genomes (pseudo diploid)
—-discont. minus strand synthesis involved in subgeneric RNA synthesis ( recombination is frequent)
what factors affect rates at which variability is introduced?
RNA or DNA genome
genome organization—>
seg or not OR diploid or haploid
—> seg required for reassortment
—> pseudodiploid shows enhanced recombination
what affect frequency that variation is observed?
selection–> need to maintain viability
what are evolutionary constrains on virus variability?
selective pressures vs requirements–> surface epitopes and receptor recognition & use must maintain fitness
what is conserved and variable on CoV spike RBD?
the fusion machine and peptide stays same
but lots of variability on the binding domain at top
what is attenuation?
how does this work in tissue culture?
-generating virus that retains infectivity but is less virulent than wild type
–viruses loose genes they do noted
—viruses grow in tissue culture loose genes required only for host immune evasion
–type of environmental adaptation
what was the issue of myxoma?
evolved to restrain its lytic potential
—viral genomes are able to establish themselves in a host population and may evolve to be less lethal so that it still can infect–< survival is ensured
why people still suffer from rhinovirus?
—over 100 serotypes!
how might influenza burden the US in seasonal epidermis?
vaccines are 40-80 effective —> millions becomes infected
—1 percent are hospitalized–> 1/1000 die
why are retroviral genomes pseudo diploid?
why are they more prone to genetic recombination ?
what is present in resulting provirus ?
only type of virus that have 2 complete copies of genetic info
–proximity of 2 RNA during RT lets template switching & recombination
–only one version present in provirus–> so one is preserved for future generations rather than 2
When there is a very little difference between the dose of a drug that kills a virus and a dose that causes serious adverse reactions in patients,
this drug has a narrow therapeutic index
