virus classification structure and replication Flashcards
theories of virus origin
cellular - viruses were once a cellular component
autopoeitic - viruses were once autopoeitic but became dep upon cells to replicate
viruses can be classified based on
virus particle structure genome replication features serology stability
a virus’s nucleocapsid is composed of
DNA/RNA core
protective capsid coating made of proteins
what’s a capsomere
repeating protein subunit of a capsid
some viruses acquire an _____ upon exiting the host. this can be dissolved using a _________
envelope
lipid solvent
how can bacterial genome be arranged?
single / double stranded and RNA or DNA
what’s the difference btween plus sense ssRNA, minus sense ss RNA and ambisense?
plus = can be used directly for prot translation minus = the antithesis of what's needed for prot translation ambisense = can code for different proteins depending on direction it's being read
what do DNA viruses need that RNA viruses don’t?
access to the nucleus
what do RNA viruses need that DNA viruses don’t?
RNA dep. RNA transcriptase,
-ssRNA and dsRNA must bring their own polymerase into the cell (+ssRNA can act as mRNA)
traits of viral receptors
- usually don’t mimic cell receptor’s normal ligands (binds to diff spots)
- typically are spike lke projections on particle surface
- may need a co-receptor
how can we change receptor recognition?
genetic engineering (integrin RGD sequence or pseudotyping particles)
pathways for viral entry
- endocytosis or direct penetration (pores or membrane disruption)
all viruses excpet ______ have to leave the nucleocapsid to be replicated
dsRNA
all viruses need cells _____ to produce proteins w/ no exceptions.
ribosomes
what’s the fate of stuctural vs. non-structural proteins?
structural go into the capsid
non-structural are only in the infected cell
how does replication work in a +ssRNA?
genome serves as template for translation
polymerase mades -ssRNA copy as template for new genomes
how does replication work for a -ssRNA?
virus particle must include viral polymerase
polymerase makes mRNA
genome replicates through full length +ssRNA intermediate
how does replication work for a dsRNA
virus particle includes viral polymerase
dsRNA induces innate immune response so it stays w/in the capsid
mRNA is syth. in the particle and exported to cytoplasm
mRNA serves as + strand in virus genome and -strand is synth from it during assembly
how does replication work for ssDNA and dsDNA?
most must gain access to nucleus (pox = exception)
prep cell for DNA replication (some need cell to be in active replication)
ensure genome ends are copied
different mechanisms of virus assembly
adenovirus - empty protein coat imports genome
reovirus - RNA packaged during capsid assembly
retrovirus - preassembly on a membrane
traits of virus replication kinetics
one step growth curve where every cell’s infected at the same time and every cell dies at the end of the infection (timed from start of infection to the beginning of the plateau
phases of virus replication kinetics
eclipse - attachment and uptake
exponential growth - replication and assembly
plateau - cell death
one step growth curves are good to assess
mutations, cell entry and process design
what is serology
antibody based viral detection
different assays used for virus detection
cytopathic effect - cell rounding, syncytia formation (cells fuse together), inclusion bodies (cells look like bricks)
fluorescent focus assays - infect cells and stain virus antigens with fluorescent antibodies
plaque assay - inoculate a cell monolayer w/ a dilute virus that will kill cells leaving clear areas.
infectious dose - inoculate either tissue cultures, eggs or animals with different dilutions of virus and see effects.
particle assays - either seen w/electron microscopy or bind w/ blood in hemagglutinin assay (red spots means not enough virus to stop blood from clumping)
genome assay - polymerase chain rxn or DNA/RNA blots
serological assays - antibody binding
