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12 Cards in this Set
- Front
- Back
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what is a virus composed of
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a set of genes (RNA or DNA) packaged in a protein containing coat; some have lipid bilayer envelopes; complete particle termed a virion
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what are 2 classes of infectious agents that are smaller than viruses
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viroids which are RNA molecules without protein shells (they invade plants); prions that are proteins without apparent genes
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properties of viruses
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intact virions are infectious; intact virion is inert or dead; virus can only replicate (aka be alive) when it has been disassembled; any processes not provided by the cell most be encoded in the virus genome; obligate intracellular parasites; dependent on host cell for ENERGY AND PROTEIN synthesis (only unique characteristic because the others can describe bacteria); filterable agents
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what is the virion composed of
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genome, capsid, envelope (those without an envelope are naked), accessory proteins
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genome structure of viruses
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DNA genomes are wither double (ds) or single (ss) stranded; RNA genomes are double or single stranded where the ss genomes have sense (positive sense, negative sense, or ambisense (+ and -) and the negative sense genomes can be segmented or nonsegmented
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what is the viral capsid for
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stability, protection of nucleic acid, resistance to environment, and are often transmitted with fecal oral transmission
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viral symmetry
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the shape of the nucleocapside; iscosahedral symmetry= approximates a sphere, all human DNA viruses EXCEPT poxviruses (complex), most + ssRNA viruses EXCEPT coronaviruses (helical) and retroviruses (complex); also called CUBIC symmetry and viruses described as SPHERICAL; helical symmetry= cylindrical nucleocapsid, usually - ssRNA viruses, rod shaped
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the viral envelope
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they are labile; sensitivity to drying and solvents; often transmitted via the respiratory droplet or blood borne routes
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function of viral glycoproteins
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the region for attachment to the cellular receptor is exposed on the spike protein's surface; under mild acidic conditions the hemagglutinin folds over to bring the virion envelope and cellular membrane together and exposes a hydrophobic sequence to promote fusion
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classification of viruses
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families and subfamilies= genome type and structure, replication strategy, symmetry, presence of absence of envelope; genera= host range, serologic reactions; species= amino acid sequence of proteins, nucleic acid homology; strain= variations in nucleic acid sequences of viruses isolated from a particular location
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naked capsid virus=
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DNA or RNA + structural proteins + enzymes and nucleic acid binding proteins = nucleocapsid = naked capsid virus
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enveloped virus=
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nucleocapsid + glycoproteins and membrane = enveloped virus
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