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ID 6.6


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Small, obligate intracellular parasite
Genome: DNA/RNA that directs host assembly of new virions
Viral Classification/Nomenclature
Historically based on disease symptoms
Now, based on physiochemical properties
Viral Classification
(useful properties)
Nucleic Acid
Structure: capsid size, shape, (+)/(-) envelope
Viral protein coat
Composed of repeating proteins or capsomeres
Aggregate of structural units that comprise viral capsids
Viral nucleic acid + capsid
Enveloped Viruses
Nucleocapsid + cell membrane (derived from host)
Membrane includes viral surface glycoproteins
Naked vs. enveloped viruses
Enveloped viruses tend to be less stable
Envelope Glycoproteins
Encoded by virus
Inserted into membrane prior to budding
The complete virus particle
Structural pattern of viruses
Cubic (icosohedral - 20 sides), helical or complex capsid
May/may not be enveloped
"SPARE the coat"
(Functions of viral coat protein)
Receptor-binding (attachment to host cell)
Enzymatic activity
What structural component determines viral antigenicity?
The coat protein
DNA viruses
DNA = mRNA template and self-replication
Majority are dsDNA
If ssDNA, virus first synthesizes 2nd strand to make dsDNA
RNA viruses
May be ss/dsRNA
Can have single/multiple segments
Single segment can be (+)/(-)
If (+), serves as mRNA
If (-), must create (+)
Viral Genome Mutation
(point mutation)
Important mechanism of mutation in RNA VIRUSES
Why? The RNA polymerase is inherently clumsy and makes many mistakes
Majority of mistakes are deleterious but occasionally may result in an advantageous mutation
Viral Genome Mutation
Between RNA molecultes
Homologous: between long, like strands often during synthesis of (+) RNA
Viral Genome Mutation
Exchange of viral segments
(obviously only works in viruses w/segmented genomes and coinfection of same host cell)
Method of Viral Classification
Family, Genera, Type, Strain
Viral Classification Parameters (Family)
Biochemical/physical parameters
NA type and replication strategry
Viral Classification Parameters (Genera)
Physical/chemical proteins
Shared antigenicity
Viral Classification Parameters (Type)
Viral Classification Parameters (Strain)
The "event" surrounding infecotion (i.e. when, where, etc)
". . . virales"
Denotes ORDER
". . . viridae"
Denotes FAMILY
". . . virinae"
". . . virus"
Denotes GENERA
Emerging Viruses
Either newly appeared in population or is expanding its host range (corresponding increase in detectable disease)

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