Virus classification, structure, and replication Flashcards
how was TMV discovered as a virus not bacteria?
it could pass thru a filter, and abcteria couldn;t bc size
what is a bacteriophage
bacteria viruses with expanded virology and biology
foot and mouth
1st animal virus
yellow fever
first human virus
are viruses smaller than bacteria, fungus, and other microbes?
yes
biological classification of viruses
obligate intracellular parasites
2 theories of virus origin
- cellular: viruses were once cellular components but over time evolved separately
- autopoietic: once autopoietic entities, became dependent on cells for replication
what is virus classification based on
- particle structure
- genome
- replication features
- serology
- stability
what is particle structure
composition, shape, size
nucleocapsid
- RNA/DNA in a core protected by a protein coat (capsid)
- structure that defines virus (helical, pleomorphic, icosahedral)
- composed on repeating protein units called capsomeres
envelopes
virus modified cellular membranes acquired upon exit from host
*exposure to lipid solvents makes enveloped viruses non infectious
smallest and largest virus
18 nm, 300 nm
virus genome
composition can be single/double stranded DNA, single/double/ +ss, -ss RNA
+ssRNA
may be directly translated
-ssRNA
must be converted to + by RNA polymerase before translation
steps of virus replication
- attachment
- entry
- transcription
- translation
- genome replication
- assembly
- release
attachment
- virus receptor -> cellular receptor
- viral receptors may require co receptors
- major determinant of host range (tropism)
entry
- receptor mediated endocytosis OR direct penetration
- non enveloped viruses: thru pores (picornavirus), membrane disruption (adenovirus, reovirus)
- enveloped viruses: membrane fusion (influenza)
*many RNA viruses replicate in membrane complexes
transcription
- production of mRNA for protein synthesis
- -ssRNA must bring own polymerase into cell
translation
- protein production
- all viruses need cell’s ribosomes for this
- regulation of protein production can occur at transcript/translat level
genome replication
- +ssRNA genome is template for translation, polymerase makes -ssRNA for new genomes
- -ssRNA: virus must include polymerase
- dsRNA: particle includes polymerase, innate immune response allows genome to stay in particle, mRNA synth in particle and released to cytoplasm, mRNA is + strand in genome
- ss/dsDNA: must gain access to nucleus, prepares cell for replication, genome is copied
assembly
- packing new genomes into functional particles
- structural proteins help
- adenovirus: empty protein coat imports genome
- reovirus: RNA packed during capsid assembly
- retrovirus: preassembly on membrane
release
- lysis: best known for bacteriophage
- weak lysis: dependent on membrane breakdown after cell death
- budding (enveloped only): cell membrane becomes outer coat of virus particle
kinetics phases
eclipse: attachment and uptake
exponential growth: replication and assembly
plateau: cell death
initial discovery of virus
- disease in host
2. contamination in cell culture
confirmation of virus
- purification of virus
- confirmation of disease
- cell culture
