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