Medical Micro - virus Flashcards
what percentage of viral proteins form the capsid
50-90%
how does viral genome size vary
4-2500 coding genes
what are viroids
circular ssRNA
no protein capsid
no protein-coding gene
mostly present in plant pathogens
outline regressive theory of viral origin
free-living organisms became parisitic
over time they lost alot of their function - explains small genome size
what are the disadvantages of the regressive theory
there is too large a gap between a virus and the simplest of parasites
outline the escape theory of viral origin
genetic material that escaped from larger organisms
there are other examples of this like transposons
what is the main drawback of the escape theory to viral origin
doesn’t explain viral structure
outline the ancient theory of viral origin
self-replicating molecules from pre-cellular world
explains fundamental difference between virus and other life
what is the drawback to the ancient theory of viral origin
unexplained how virus-ancestors replicated without a host
how are viruses classified
based on structural traits:
capsid
nucleic acid type
absence/presence of envelope
what are the 7 classifications of life and which do viruses check
organisation -/
metabolism
response to stimuli
homeostasis
growth
reproduction -/
evolution -/
what are the 5 steps of viral replication
attachment
penetration
nucleic acid and protein synthesis
assembly and packaging
release - lysis
outline the basics of how HIV binds to CD4
binds to CCR5/CXCR4
still too far, requires co-factors to fuse membranes
what is the difference between how non-enveloped/enveloped animal viruses penetrate
non-enveloped - enters via endocytosis
enveloped - enters via fusion, needs uncoating of nucleocapsid to release nucleic acids
how do viruses enter plant cells
cell wall makes it harder so they find damaged cell walls to enter
or they use a vector
how do virus inject their material into a bacterial cell
bacterial cell wall is too rigid to cross
so the virus binds to the surface
the tail sheath contracts and the tail core is pushed through the cell wall and the genetic material is injected into the cytoplasm
sound familiar?
what is the difference between DNA virus and RNA virus synthesis
DNA - can be synthesised by host cell machinery
RNA - need to synthesis it themselves
because RNA-dependent RNA polymerase is absent in the host
what can genomic RNA act as in some RNA-viruses
functions as mRNA
outline the process of budding
virus is within an endosome
nucleic acid and capsid separate
nucleic acid encodes for envelope proteins
nucleic acid returns to capsid
envelope proteins join at the exosome
progeny virus is released from the cell
difference between vertical and horizontal gene transfer
vertical - transfer of genetic material from parent to offspring
horizontal - transfer from one lineage to another
features of mimivirus/mamavirus/megaviruses
large viruses infecting amoebae
400-800nm
~1000 protein coding genes
how large is an E. coli approx.
~ 2μm x 500nm
features of sputnik viruses
small virus infecting amoebae
virophage
when can sputnik viruses infect amoebae
cannot infect amoebae on its own
can only infect it if its already infected by a mimi/mamavirus
features of pandavirus
largest virus genome - 2x the size of a megavirus
~ 2500 protein-coding genes
infects amoebae
features of pithovirus
found in siberian permafrost
1.5μm x 500nm
infects amoebae
features of medusavirus
infects amoebae
forces host to form a thick hardened shell
what could this be?
features of polydnavirus
it is an insect virus found in parisitoid wasps
incorporated in wasp genome
only reproduces using wasp’s reproductive system
injected via eggs and enter host blood cells
reduces immune response
