viruses Flashcards
why do viruses differ from all other life forms
no functional organelles
only replicate within a host
cannot produce their own energy
metabolically inert outside of host
what kind of parasite are viruses
obligate
replication of virus within host cell usually causes
cell death and eventually disease
viruses consist of what kind of nucleic acid
either DNA or RNA
what is a viruses nucleic acid surrounded by
a protein coat called the capsid
some viruses have another layer around the capsid, what is it
the envelope, which contains membrane proteins that extend outwards
size range of common viruses
20-300 nm diameter, some much larger
3 shapes of virus capsids
helical (cylindrical or rod shaped), icosahedral (3D and somewhat round) and complex
what could the viral genome be
dsDNA, ssDNA, dsRNA OR ssRNA
what shape is the virus genome usually
single linear or circular molecule
so either RNA or DNA, ss or ds, linear or circular (except ds circular for RNA does NOT exist)
we know some virus have a segmented genome comprised of multiple parts, what is this called
multi-partite
how do viruses recognize host cell
surface cell receptors
how do viruses multiply in host
they use host cell machinery to produce new nucleic acid and proteins, new virions are assembled and leave host cell, cell often destroyed in process
viruses classified into groups according to:
type of nucleic acid
shape of capsid
envelope or not
replication strategy
genome sequence and organization
other criteria such as size, pH sensititvity, host range etc
***NOT TYPE OF DISEASE CAUSED BECAUSE VIRUSES OF SAME FAMILY CAN CAUSE RANGE OF DISEASE
name a type of enveloped, dsDNA virus
herpesvirus
name a type of non enveloped dsDNA virus
adenovirus
name a type of non enveloped ssDNA virus
parvovirus
name type of enveloped ssRNA virus
coronavirus
name type of non enveloped dsRNA virus
reovirus
name a type of non enveloped ssRNA virus
calicivirus
how do you classify virus
family, then genus, then species (which is usually type of disease caused)
usually call them by species name
what are viruses name after
usually the disease they cause but sometimes named after place they were first isolated
should you italicize viruses
previously no but now YES (not widely accepted)
why might people believe viruses existed only after evolution of first cellular life
because they are obligate intracellular parasites, rely on other cells
why might believe believe viruses came before evolution of first cellular life
because they are simply molecular genetic parasite and could of parasitized and nucleic acid/ protein replication system including prebiotic systems (before life)
what are issues with virus evolution
-no fossils
-huge diversity of viruses, do they have different ancestors?
is it clear that some viruses do have lineages and evolutionary relationships
yes
what is virus evolution theory 1
viruses are escaped pieces of host cell DNA (genes coding for replication enzyme and genome coating protein)
why might virus evolution theory 1 be right
fits with some DNA viruses that use host-like replication processes, also fits with retrovirus which insert a DNA copy of their genome into host cell and can “pick up” host cell genes when virus replicates
why might virus evolution theory 1 be wrong
emergence of a full virus genome has never been observed and genetic analysis doesn’t indicate a cellular origin for most DNA viruses
what is virus evolution theory 2
-viruses are degenerate unicellular life forms (may have once be small cells that parasitized larger cells and over time genes that were not required were lost)
why might virus evolution theory 2 be right
fits with large DNA viruses which psychically resemble bacteria and have complex genomes
why might virus evolution theory 2 be wrong
sequence of viral genomes indicates that they did not originate from bacterial or other unicellular genomes, instead they have distinct viral lineages
what is virus evolution theory 3
viruses originated independently from host cells, with several separate viral origins occurring at different times
RNA virus may have origins in the RNA world
DNA viruses likely co evolved w their hosts while the DNA world was developing
which virus evolution theory has most supporting evidence
3
how are many of major viral diseases controlled
vaccination programs
are viruses the top of the list as the cause of emerging diseases
yes, because, mutations expand host range and increase virulence
as well disruption to ecosystems and social factors bring animal species closer together
provide an example of different types of viruses of veterinary significance
henipavirus: hendra and nipah viruses
both viruses maintained in flying fox fruit bats
trasnmit to humans via horses (hendra) or pigs (nipah) or directly from bats
