Virus - Basics & News
Taxonomy & 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 cell
for 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 structur
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
non enveloped Virus: contains only nucleic acid
and protein
Tobacco mosaic virus:
helical capsid
Adenovirus:
icosahedral capsid
‘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 carry
structures for binding to cellular receptors
These both (non related) viruses bind to CAR but the binding structures look
very different
‘Canyons‘ for binding to CAR
(many enterovirus types)
Fiber (‘Spikes‘) for binding
to CAR (many adenovirus
types)
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
RNA-Virus
RNA viruses
DNA-Virus
DNA viruses
Baltimore System
way of mRNA production (->Proteinsynthesis)
DNA Virus
RNA Virus