test four lec 19 Flashcards
what are acute viruses
kill their host
what happens in lysogenic cycle
bacteriophage is quiescent
integrates into cell chromosome as prophage
can reactivate to become lytic
transduction
what are prions
proteins that infect animals
what is a viral capsid composed of
repeated protein subunits
maximizes capacity while minimizing the required number of genes
how does slow release work
filamentous phages can extrude individual progeny through cell envelope
host cells grow slowly but dont die
use SS DNA to create DS DNA and reproduce
what makes ocean viruses different
most numerous and genetically diverse forms of life
control algae bloom
viral ecologists believe what of viruses
living entities
predator or parasite
how are animal viruses cultured
within whole animals by serial inoculation
ensures virus maintains its original virulence
can also grow in human cell tissue culture
what is the function of a capsid
packages the viral genome and delivers it into the host cell
they vary based on virus
what are the seven fundamental groups of viral species by baltimore virus classification
DS DNA SS DNA DS RNA \+ SS RNA - SS RNA RNA retrovirus DNA pararetrovirus
what dictates wether lytic or lysogenic
environmental cues
threaten host cell survival
what type of defenses have bacteria created against bacteriophage infection
genetic resistance (alter receptor proteins) restriction endonucleases CRISPR (integration of phage DNA sequences) bacterial immune system
how can you measure relatedness of different viruses of a common ancestor
comparing their genome sequence
what is a virus
a non cellular particle that must infect a host cell, where it reproduces
what is used to reveal common descent of viruses with shared infected hosts
statistical analysis
what are viroids
RNA molecules that infect plants
what allows viruses to attach to host cells
cell surface receptors
what is the baltimore virus classification
primary distinction among classes of viruses is genome composition and the route used to express messenger RNA
how are viral genomes classified
baltimore method viral proteins capsid envelope proteins polymerase
how does lysis work
make enzyme that breaks down cell wall
host cell bursts to release progeny phage
what type of curve do batch cultures of viruses create
step curve
what is the envelope like in an icosahedral virus
contains glycoprotein spikes
teguments are present inbetween the envelope and capsid
what is a virion
a virus particle
do viruses play a significant role in carbon balance
yes
when do you use proteomic classification
useful of viruses because their small genomes encode few proteins
how do viruses fill important niches in all ecosystems
limiting host population density
selecting for host diveristy
what type of genome do large viruses have
more than 100 genes
what are bacterial cell receptors used for
sugar uptake (maltose)
how does a new virus emerge to sicken humans
humans eat wildlife
(SARS)
as variants of endemic milder pathogen
(H7N9)
what environment can you find viruses
all types
what are the characteristics of a filamentous virus
capsid consists of a long tube of protein genome coiled inside vary in length (genome size) include bacteriophage and animal viruses helical symmetry (tube around genome) usually contain ss DNA and RNA
what type of organism does viruses infect
all types
what are cell surface receptors
proteins that are specific to the host species and which bind to a specific viral component
what are the two types of life cycles of bacteriophages
lytic
lysogenic
how do viruses infect hosts
mimicking by spreading “computer viruses” whose info “infects” computer memory
the pox virus has what type of capsid
genome surrounded by several layers
(core envelope with outermembrane)
contain large number of accessory proteins
how do you culture viruses
requires growth in host cell
bacteriophages cultured either in batch culture or as isolate plaques on a bacterial lawn
how do viroids replicates
they use the host RNA polymerase
what are the characteristics of icosahedral viruses
polyhedral
20 identical triangular faces
rational symmetry
capsid is enclosed in an envelope
acute vs persistant viruses
acute outnumbers in natural ecosystems
what are orthologs
genes of common ancestry in two genomes that share the same function
what is the criteria that is used by the ICTV over virus taxonomy
genomes composition capsid symmetry envelope size of the virion host range
what are the two types of symmetrical viruses
icosahedral and filamentous
what are the two types of capsids
symmetrical and asymmetrical
what happens in the lytic cycle
bacteriophage quickly replicates killing host cell
cause cell to burst, releasing new phages
what type of genome do small viruses have
small
encoding under 10 genes, which may overlap in sequence
what does a virion consist of
a single nucleic acid (DNA or RNA) contained within a protective protein capsid
what are persistant viruses
along for the ride
may evolve traits that confer positive benefits in a virus-host mutualsim
what is needed for host infection
host recognition and attachment
genome entry
assembly of virions
exit and transmission
what is transduction
take host genome and pass it on to other cells
how do most viruses interact with hosts
positively
express host genes and by protecting hosts from other organisms
what characteristic does T4 bacteriophages have with asymmetrical
have icosahedral head and helical neck
what are proteoms
proteins encoded by genomes
what is injected from phages into host cell
only genome through cell envelope
phage capsid remain outside
“ghost”
characteristic of asymmetrical viruses
complex multipart structures
what is required for viruses to replicate
require host cell
do viroids have protein capsids
no
what makes prions different
they have NO nucleic acid component
have abnormal structure that alters the conformation of other normal proteins
what type of genome comparison is used when finding common ancestor
orthologs
