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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