Virology Flashcards
what is a virus
genetic element that can replicate only inside a living cell
what do viruses rely on the host cell for
energy , metabolic intermediates, and protein synthesis
what is the extracellular form of a virus
virion
a virus cannot replicate until it has done what
infect a host cell
how large are viruses
20-300nm
how many base pairs do viruses have
less than 700kbp
what is essential to the survival of a virion
the capsid
what is a capsid
a protein sheath containing the virus genome
what types of host does a virus use if it doesnt have a capsid
probably bacterial
if a virus has a capsid, what will it most likely use as its host
animal
what is it called when a virus has no envelope
naked
what is the envelope of a virus made of
protein plus lipid
what is the purpose of the virion
to protect the virus when it is outside of a host cell
what is a nucleocapsid
inner structure of nucleic acid plus the capsid protein (the whole thing)
what are the two ways a virus can infect the host
lytic or lysogenic
what is lytic infection
virus redirects hosts metabolism to support virus replication (host cell destroyed)
what is lysogenic infection
host cell is not destroyed but is genetically altered and the virus genome becomes part of the host genome
what is the protein that a capsid is made up of
capsomers
what is the nucleic acid for viruses
DNA OR RNA
how are virus nucleic acids further divided
single or double stranded, plus sense or minus sense
what is the shape of viral genomes
circular or linear
what is viral plus sense RNA synonymous to
exact same base pairing as viral mRNA
what is viral minus sense RNA
complimentary base pairing to viral mRNA
what types of viruses typically have the smallest genomes
RNA have smaller genome than DNA
what is another name for bacterial viruses
bacteriophages
virion assembly being a spontaneous process what is it called
self assembly
what are the two primary shapes for a virus
rod or spherical
what kind of symmetry do rod shaped bacteria have
helical
what kind of symmetry do spherical viruses have
icosahedral symmetry
where does a non-enveloped virus get its envelope from
it gets it from the host cell upon infection (takes host cell membrane)
how many faces does an icosahedron have
20 triangular faces and 12 vertices
axes of symmetry divide an icosahedron into how many segments
5, 3, or 2
is an icosahedron or a rod preferable to a virus
icosahedron is preferred because it takes less capsomers to make
what is the most complex viral shape
head-plus-tail
most enveloped viruses affect what
animals
why do you not find enveloped viruses in bacteria and plants
because they have cell walls and these are much more difficult tp penetrate
why are envelopes so important to viruses
its what comes into contact with animal cells and the two membranes must fuse before penetration
what on the virus envelope allows for attachment to the host cell
there are embedded proteins in the virus envelope (often glycoproteins)
what do naked viruses use to attach to the host cell
peplomers
what must a virus do first in order to replicate itself
it must take infect a host cell
why can a virus not use a dead host cell in order to replicate
there are energy requirements so it needs a living cell to get energy from
what are the 5 steps of viral replication
attachment, penetration, synthesis, assembly, release
what happens in attachment of a viral cell
virus attaches to host
what happens in penetration of a virus
enters host cell and injects its genome
what happens in synthesis of a virus
makes new genetic material using the host cell energy and nutrients
what happens in assembly of a virus
package genomes into new individual viruses
what happens in the release of viruses
viruses are released from the host cell (lysis)
what are the ways virions can be released from a cell
lysis, budding, excretion
when we treat viral infections what are we trying to do
trying to use antibodies to block attachment of virus to host cells
what are two ways that a virus can resist the defenses of the host
restriction endonucleases
nucleic acid modifications
what is a temperatre virus
double stranded DNA virus that can infect host long term in a stable relationship
what nucleic acid does class 3 viruses have
double stranded RNA
what nucleic acid does class 4 viruses have
single strranded positive RNA
what nucleic acid does class 5 viruses have
single stranded negative RNA
what nucleic acid does class 6 viruses have
single stranded positive RNA
what nucleic acid does coronaviruses have
ssRNA (+)
what nucleic acid does the polio virus have
ssRNA(+)
what kinda of viruses have ssRNA(-)
rhabdoviruses, orthmyxovirus, paramyxovirus
how are viruses identified for immunizations
H_N_
what does H refer to
hemagluttinin
what does N refer to
Neuraminidase
what kind of nucleic acid does class 1 and 7 viruses have
dsDNA
what kind of nucleic acid does class 2 viruses have
ssDNA(+)
what class of viruses uses reverse transcriptase
class 6 viruses
what is reverse transcription
process of copying RNA into DNA
what is the phenomena of overlapping genes
insufficient DNA to encode all viral-specific proteins unless parts of the genome are read multiple times in different reading frames
why is hemagluttinin so important in immunizations
hemmaglutinin is highly immunogenic
what is the function of neuraminidase
breaks down sialic acid in host cytoplasmic membrane
why does antigenic shift occur
RNA makes mistakes and cannt go back and fix them like DNA can
why does antigenic drift happen
more so mutations to the virus over time (much slower than shift)
what are the two sub viral particles
viroids and prions
what do viroids typically infect
plants
what are viroids most importantly missing
proteins
what do prions infect
only animals
what important thing are prions lacking
no nucleic acid
what do prions transmit
spongiophore enecephalopathies (mad cow disease, scrapie)
how do prions do their damage
cause proteins in host cells to fold incorrectly, losing their function
