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HCD 12203
Basic Medical Microb
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INTRODUCT
VIRU
HCD 1Basic MMicrob
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VIRUSES
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General Structure of Viruses Size range
most
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General Structure of Viruses Capsids
All viruses have capsids - protein coats that enclose and
protect their nucleic acid. Each capsid is constructed from identical subunits called
capsomers made of protein. The capsid together with the nucleic acid are
nucleoscapsid.
Some viruses have an external covering called enthose lacking an envelope are naked
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Two Structural Types
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Two Structural Types
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General Structure of Viruses Viral envelope
mostly animal viruses acquired when the virus leaves the host cell exposed proteins on the outside of the envelope, called
spikes , essential for attachment of the virus to the hostcell
99
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Functions of Capsid/Envelope Protects the nucleic acid when the virion is outside the
host cell Helps to bind the virion to a cell surface and assists the
penetration of the viral DNA or RNA into a suitable hostcell
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General Structure of Viruses Complex viruses: atypical viruses
Poxviruses lack a typical capsid and are covered by a
dense layer of lipoproteins. Some bacteriophages have a polyhedral
nucleocapsid along with a helical tail and attachmentfibers.
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Nucleic Acids DNA viruses
usually double stranded(ds) but may be singlestranded (ss)
circular or linear RNA viruses
usually single stranded,may be doublestranded, may besegmented intoseparate RNA pieces
ssRNA genomes readyfor immediate 1212
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General Structure Pre-formed enzymes may be present.
polymerases DNA or RNA replicases copy DNA reverse transcriptase synthesis of DNA from RNA
(AIDS virus)
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Classifying Viru Main criteria presently us
are structure, chemicalcomposition, and geneticmakeup.
No taxa above Family (nokingdom, phylum, etc.)
Currently recognized: 3orders, 63 families, and 2genera of viruses
Family name ends in -vir i.e. Herpesviridae
Genus name ends in vir
Simplexvirus
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r ons an er n ec ousParticles
h ll l f
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Other noncellular infectiousagents