Virus Structure & Classification

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Virus Structure & ClassificationVirus Structure & Classification

developed bydeveloped by

Hugh B. FackrellHugh B. Fackrell

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Lecture OutlineLecture Outline

Scope of virologyScope of virology NomenclatureNomenclature VirionVirion Virus genome Virus genome Virus symmetryVirus symmetry Virion structureVirion structure

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Scope of VirologyScope of Virology

In developed countries viral infections are In developed countries viral infections are the most common cause of acute disease the most common cause of acute disease that does not require hospitalizationthat does not require hospitalization

In developing countries viral infections are In developing countries viral infections are a common cause of mortality and disability a common cause of mortality and disability especially among infants and childrenespecially among infants and children

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Viruses as a health hazardViruses as a health hazard

Now antibiotics effectively Now antibiotics effectively control most bacterial control most bacterial

infectionsinfections

Viruses pose a relatively greater Viruses pose a relatively greater and less controlled threat to and less controlled threat to

human healthhuman health

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VirusVirus

obligate intracellular parasiteobligate intracellular parasite delivers its genome into host celldelivers its genome into host cell

– genome is either DNA or RNAgenome is either DNA or RNA genome transcribed and translated by host genome transcribed and translated by host

synethetic machinarysynethetic machinary

Viruses are NOT cellular

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VirusVirus

submicroscopic particlessubmicroscopic particles– smallpox a large virus is at the limit of smallpox a large virus is at the limit of

resolution of the light microscoperesolution of the light microscope– most require use of electrom microscopemost require use of electrom microscope

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Viruses Infect All Life FormsViruses Infect All Life Forms

Bacteria>> bacteriophageBacteria>> bacteriophage PlantsPlants FungiFungi InsectsInsects FishFish ReptilesReptiles BirdBird MammalsMammals

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Viral NomenclatureViral Nomenclature

viruse families end with -viruse families end with -viridaeviridae– eg poxviridae retroviridaeeg poxviridae retroviridae

Virus subfamilies -Virus subfamilies -virinaevirinae– alphaherpesvirinae herpes simplexalphaherpesvirinae herpes simplex– gammaherpesvirinae- epstein Barr virusgammaherpesvirinae- epstein Barr virus

Virus genera -Virus genera -virusvirus– enterovirus- polio virusenterovirus- polio virus– lyssavirus -rabies viruslyssavirus -rabies virus

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SiglumSiglum

An abbreviation derived from a few or An abbreviation derived from a few or intial lettersintial letters

– (plural (plural siglasigla))

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Virus SiglaVirus Sigla

RRespiratory espiratory EEnteric and nteric and OOrphan rphan VirusViruseses PaPapilloma, pilloma, PoPolyoma & lyoma & VaVacuolating agent cuolating agent

VirusViruseses HepaHepatocytes & tocytes & RNARNA genome genome

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Sigla (cont)Sigla (cont)

Parvovirus -smallParvovirus -small Adenovirus - gland eg adenoid tissueAdenovirus - gland eg adenoid tissue Herpes- creeping- nature of lesionsHerpes- creeping- nature of lesions Toga virus - cloaked with envelopeToga virus - cloaked with envelope Arena virus - sand like lesionArena virus - sand like lesion Corona virus- crown like peplomersCorona virus- crown like peplomers Bunya virus - Bunyamwera AfricaBunya virus - Bunyamwera Africa Calcivirus - cup likeCalcivirus - cup like

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Herpes zosterHerpes zoster

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VirionVirion

A fully assembled infectious virusA fully assembled infectious virus At least two componentsAt least two components GenomeGenome

– DNA or RNADNA or RNA

– Single stranded or double strandedSingle stranded or double stranded

– Sense or antisenseSense or antisense CapsidCapsid

– Protective protein coatProtective protein coat

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DNA VirusesDNA Viruses

Parvovirus Parvovirus ssDNA, sense or antisense, ssDNA, sense or antisense, linearlinear

HepadnaAvirusHepadnaAvirus dsDNA,linear dsDNA,linear Papovavirus Papovavirus dsDNA,circulardsDNA,circular Adenovirus Adenovirus dsDNA,lineardsDNA,linear Herpes virus Herpes virus dsDNA,lineardsDNA,linear Pox virus Pox virus dsDNA, lineardsDNA, linear

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RNA VirusesRNA Viruses

ssRNA, Sense strand ssRNA, Sense strand -picornavirus, -picornavirus, calicivirus, togavirus, coronaviruscalicivirus, togavirus, coronavirus

ssRNA, antisense strand ssRNA, antisense strand -bunyavirus, -bunyavirus, orthomyxovirus, arenavirus, filovirus, orthomyxovirus, arenavirus, filovirus, rhabdovirus,paramyxovirusrhabdovirus,paramyxovirus

RetrovirusRetrovirus ssRNA 2 copies ssRNA 2 copies ReovirusReovirus dsRNA, 10-12 segments dsRNA, 10-12 segments

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CapsidCapsid

Protein coat that protects the genomeProtein coat that protects the genome protection against nucleasesprotection against nucleases few structural proteinsfew structural proteins

Capsids Self Assemble

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Virion SymmetryVirion Symmetry

Cubical SymmetryCubical Symmetry– AdenovirusAdenovirus– picorrnaviruspicorrnavirus

Helical SymmetryHelical Symmetry– FilovirusFilovirus– RhadovirusRhadovirus

Complex SymmetryComplex Symmetry– poxviruspoxvirus– T4 bacteriophageT4 bacteriophage

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Helical SymmetryHelical Symmetry

Helical rigidHelical rigid– Rhabdovirus,-rabiesRhabdovirus,-rabies

Helical pleomorphic Helical pleomorphic – Paramxyovirus -parainfluenzaParamxyovirus -parainfluenza– ,measles & respiratory syncytical virus,measles & respiratory syncytical virus– Orthomxyovirus -influenzaOrthomxyovirus -influenza

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Helical SymmetryHelical Symmetry

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RhabdovirusRhabdovirus

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Cubic SymmetryCubic Symmetry

Icosahedral SymmetryIcosahedral Symmetry 20 equilateral triangles20 equilateral triangles 12 vertices12 vertices 532 symmetry532 symmetry

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Icoshedral StructureIcoshedral Structure

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Complex SymmetryComplex Symmetry

Very rigid, defined structuresVery rigid, defined structures may or may not have envelopemay or may not have envelope

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Complex SymmetryComplex Symmetry

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Polio VirusPolio Virus

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PeplomerPeplomer

Glycoprotein spikesGlycoprotein spikes on viral envelopeon viral envelope coded by viral genomecoded by viral genome coronavirus,orthomyxovirus, coronavirus,orthomyxovirus,

arenavirus,Rhabdovirus,paramyxovirusarenavirus,Rhabdovirus,paramyxovirus

Determine viral host range

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Viral EnvelopeViral Envelope

Some viruses are surrounded by an Some viruses are surrounded by an additional covering - viral envelopeadditional covering - viral envelope

derived from host cell membranesderived from host cell membranes contact virus proteins internallycontact virus proteins internally glycosylated proteins externallyglycosylated proteins externally

50% of animal viruses have an envelope