Virology2 Flashcards
which viruses are naked icosahedral?
hepatitus A
polio viruses
which viruses are enveloped icosahedral?
yellow fever
herpes simplex
HIV
which viruses are enveloped helical?
influenza,
mumps,
measles,
rabies
which viruses are complex w many proteins (some combos of icosahedral & helical capsid structures) ?
herpesviruses
smallpox
hepatitis B
T4 bacteriophage
which viruses are circular?
papillomaviruses
many bacteriophages
which viruses is non-segmented?
parainfluenza viruses
which viruses are segmented?
influenza viruses
what is rolling-circle replication?
one strand of replicative form is nicked and replication enzymes are used to extend the free 3’ end
as complementary strand is synthesised around circular DNA, 5’ end is peeled off → displaced strand that continues to grow in length
what is viral reassortment?
definition + implication
- the exchange of genetic material between segments of 2 (or more) viruses of the same strain that have coinfected the same cell
- causes antigenic shift → increases pandemic potential
only in viruses w segmented genomes (flu, rota)
what is viral recombination?
- exchange of genetic material between 2 chromos of similar/related strains that have coinfected a host cell
- through crossing over of genes between 2 regions of homologous base sequences
- results in progeny w genetic material from 2 paternal viral strains
- increases genetic diversity
what is viral complementation?
- 2 viruses coinfect host cell
- virion A produces functional protein
- virion B has mutation in genome → nonfunctional protein
- no genetic info exchanged
- functional protein used in progeny of both virions
what is phenotype mixing?
- coinfection of cell w 2 related viruses
- virus A genome is partially/completed coated by surface protein of virus B → pseudoviron formation (viral hybrid)
- virus A determines genetic material of progeny
- virus B proteins determine host tropism (infectivity of hybrid virus)
- future generations lose this
what is phenotype masking (transcapsidation)?
- related viruses infect same cell
- capsid of 1 virus envelops genome of another virus
what is point mutation?
- hemagglutinin or neuraminidase genes
- causes antigenic drift → significantly increases potential of virus to cause epidemic
what are the 6 steps in a typical lytic cycle?
- attachment
- penetration
- uncoating
- replication & synthesis
- assembly
- release
APURAR
non-enveloped and enveloped viruses in the penetration step
non: via endocytosis or transmembrane transport
envelope: via endocytosis or fusion w host cell’s membrane
what does the uncoating step of the lytic cycle refer to?
nucleic acid needs to be uncoating for virus replication to begin
naked and enveloped during viral release stage
naked: released via cell lysis
enveloped: released via budding
budding doesn’t kill cells = persistent infections
what is the difference in the viral life cycle between viruses with RNA and DNA genomes?
genome of RNA virus does not enter nucleus, everything happens in the cytoplasm (unlike DNA viruses)
what are T-phages?
a series of seven phages that infect E.coli
what are the T-even phages?
- T2
- T4
- T6
what are the dependent virulent T-phages?
- T1
- T3
- T7
which T-phage is autonomously virulent and which one is well-studied?
T5 → autonomously virulent
T4 → well-studied
what are temperate phages?
become part of host chromo & replicated w cell genome until induced to make newly assembled viruses or progeny viruses
what is the difference between lytic and lysogenic cycles?
ito of definition
lytic → virus destroys host cell (rapid process w lysis)
lysogenic → viral genomes becomes integrated into host genome
describe the lysogenic cycle (5)
- latent period: host cell not killed → viral nucleic acids undergo genetic recombination
- bacterial DNA replicates = prophages replicate
- lysogenic/phage conversion (change in phenotype)
- persistin host until induction → excision of viral genome from host → proceed to lytic cycle
- lysogeny
provirus vs prophage
provise doesn’t undergo excision after splicing into genome
what are the 4 symptoms of viral infection in plants?
- hyperplasia = galls
- hypoplasia/dec in cell growth = yellowing
- cell necrosis = cell death
- malformed leaves
what are the 2 main courses of viral infection?
+ subdivisions
- acute
-
persistent
* latent infection
* chronic infection → host cell infusion
* transforming infection
what is the course of a typical acute infection?
virus prod increases → reaches threshold level → adaptive response → clear infection → antibodies, residual effector cells & memory cells = protection
what is persistent infection?
- when virus not completely cleared from system of host but stays in certain tissues or organs of infected person
- 2 main categories: latent & chronic
what is latent infection?
virus remains in equilibrium with host for long periods before symptoms again appear, but actual viruses can’t be detected until reactivation of disease occurs
HSV, chicken pox
what is slow infection?
slow virus period of a year separates the initial acute infection & fatal outcome
hep B
what is chronic infection characterised by?
continued presence of infectious viruses following primary infection
what are the 2 viruslike agents?
viroids → no coat proteins, infectious ssRNA
prions → infectious particles made of proteins, lack nucleic acid
