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Virus - Basics & NewsTaxonomy & Families
What is a virus ?
1. Structure
2. Genome
3. Replication
A virus is a virus (lat: poison)• Replication: a replicating biochemical complex without its own metabolism
•requires metabolism of living host cellfor replication
• Structure: Submicroscopic Size, 30 - 150 nm(exception:orthopox)
• Genome: contains genetic information, DNA or RNA
Virus - sizes
Comparison of Size: Virus/Bakterium
•An infectious virus particle ‘Virion‘•The genome (DNA or RNA) is always packed in a protein structure
the ‘Capsid‘•The combine Capsid/Genomestructure: ‘Nukleocapsid‘•The capsid structure can be spherical (Icosaeder)
or helical structure (Tubulus)•Some viruses have additional structures: a lipid envelope
engulfing the capsid
Adenovirus: icosahedral capsid
Tobacco mosaic virus: helical capsid
non enveloped Virus: contains only nucleic acid and protein
‘enveloped viruses‘
Herpes Simplex Virus Paramyxovirus
For enveloped viruses, the lipid envelope is always essential for infectivity.The envelops can be easily destoyed by ether & detergents
•Spherical capsids have an icosahedral structure•An Icosahedron has 20 triangular surfaces and
three axes of symmetry
Picornavirus:5-fold axes of smmetry animated X-Ray structure
• Icosahedral capsids are built from capsomers:identical units of the same proteins
X-Ray structure
capsid of picornaviridae
The capsid surface of non enveloped viruse must carrystructures for binding to cellular receptors
‘Canyons‘ for binding to CAR(many enterovirus types)
Fiber (‘Spikes‘) for bindingto CAR (many adenovirustypes)
These both (non related) viruses bind to CAR but the binding structures look very different
Comparison:replication of virus
vs. bacterium•obligat intrazellulär•NIE auf Nährmedien, Agars usw.•lebende Zellen erforderlich:
•Versuchstier•Brutei•Zellkultur
•Eklipse bzw. Latenzperiode, •Adsorption, Penetration, Uncoating• Proteinsynthese & Genomreplikation• Assembly & Virusfreisetzung
Classical Concept of ICTV
• taxonomy system: family/genus/species
• family names: ...-idae
• relevant for virus family:– genome type (DNA, RNA; ds-, ss-, )– capsid structure (helical, icosahedral)– enveloped/non enveloped
RN
A-V
iru
sRNA viruses
DNA virusesD
NA
-Vir
us
Baltimore Systemway of mRNA production (->Proteinsynthesis)
DNA Virus
RNA Virus
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