Download Virus Structure

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Virus Structure & Classification
developed by
Hugh B. Fackrell
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Lecture Outline
Scope of virology
 Nomenclature
 Virion
 Virus genome
 Virus symmetry
 Virion structure
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Scope of Virology
In developed countries viral infections are
the most common cause of acute disease
that does not require hospitalization
 In developing countries viral infections are
a common cause of mortality and disability
especially among infants and children
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Viruses as a health hazard
Now antibiotics effectively
control most bacterial
infections
Viruses pose a relatively greater
and less controlled threat to
human health
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Virus
obligate intracellular parasite
 delivers its genome into host cell

– genome is either DNA or RNA

genome transcribed and translated by host
synthetic machinery
Viruses are NOT cellular
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Virus

submicroscopic particles
– smallpox a large virus is at the limit of
resolution of the light microscope
– most require use of electron microscope
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Viruses Infect All Life Forms
Bacteria>> bacteriophage
 Plants
 Fungi
 Insects
 Fish
 Reptiles
 Bird
 Mammals
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Viral Nomenclature

viruse families end with -viridae
– eg poxviridae retroviridae
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Virus subfamilies -virinae
– alphaherpesvirinae herpes simplex
– gammaherpesvirinae- epstein Barr virus
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Virus genera -virus
– enterovirus- polio virus
– lyssavirus -rabies virus
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Siglum

An abbreviation derived from a few or
intial letters
– (plural sigla)
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Virus Sigla
Respiratory Enteric and Orphan Viruses
 Papilloma, Polyoma & Vacuolating agent
Viruses
 Hepatocytes & RNA genome
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Sigla (cont)
Parvovirus -small
 Adenovirus - gland eg adenoid tissue
 Herpes- creeping- nature of lesions
 Toga virus - cloaked with envelope
 Arena virus - sand like lesion
 Corona virus- crown like peplomers
 Bunya virus - Bunyamwera Africa
 Calcivirus - cup like
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Herpes zoster
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Virion
A fully assembled infectious virus
 At least two components
 Genome

– DNA or RNA
– Single stranded or doublr stranded
– Sense or antisense
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Capsid
– Protective protein coat
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DNA Viruses
Parvovirus ssDNA, sense or antisense,
linear
 HepadnaAvirus dsDNA,linear
 Papovavirus dsDNA,circular
 Adenovirus dsDNA,linear
 Herpes virus dsDNA,linear
 Pox virus dsDNA, linear
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RNA Viruses
ssRNA, Sense strand -picornavirus,
calicivirus, togavirus, coronavirus
 ssRNA, antisense strand -bunyavirus,
orthomyxovirus, arenavirus, filovirus,
rhabdovirus,paramyxovirus
 Retrovirus ssRNA 2 copies
 Reovirus dsRNA, 10-12 segments
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Capsid
Protein coat that protects the genome
 protection against nucleases
 few structural proteins
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Capsids Self Assemble
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Virion Symmetry
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Cubical Symmetry
– Adenovirus
– picorrnavirus
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Helical Symmetry
– Filovirus
– Rhadovirus
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Complex Symmetry
– poxvirus
– T4 bacteriophage
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Helical Symmetry
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Helical rigid
– Rhabdovirus,-rabies
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Helical pleomorphic
– Paramxyovirus -parainfluenza
– ,measles & respiratory syncytical virus
– Orthomxyovirus -influenza
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Helical Symmetry
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Rhabdovirus
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Cubic Symmetry
Icosahedral Symmetry
 20 equilateral triangles
 12 vertices
 532 symmetry
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Icoshedral Structure
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Complex Symmetry
Very rigid, defined structures
 may or may not have envelope
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Complex Symmetry
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Polio Virus
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Peplomer
Glycoprotein spikes
 on viral envelope
 coded by viral genome
 coronavirus,orthomyxovirus,
arenavirus,Rhabdovirus,paramyxovirus
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Determine viral host range
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Viral Envelope
Some viruses are surrounded by an
additional covering - viral envelope
 derived from host cell membranes
 contact virus proteins internally
 glycosylated proteins externally
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50% of animal viruses have an envelope
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