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Samenvatting les 2
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Summary of 15 pages for the course Virology at UA (Samenvatting les 2)
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Virus structuresA virus genome has two core modules that consist of proteins for genome replication (nsp) and
proteins involved in virion formation (sp)
Virus particles are made up from structural proteins
Protection of the fragile viral genome
A stable and protective protein shell
Recognition and packaging of viral genome
Interaction with cell membrane to form envelope
Delivery of the viral genome
Bind to host cell receptors
Fusion with cell membranes
Uncoating of genome
Transport of genome to appropriate subcellular localization (cytoplasma/ nucleus):
interaction with cellular proteins
Virus structures
Virion Infectious virus particle
Envelope Lipid bilayer from the host cell, E-proteins (envelope proteins)
embedded
Capsid structural unit Unit from which capsids or nucleocapsids are built: contain one or more
subunits
Subunit Single folded polypeptide chain
Nucleocapsid or capsid Protein shell surrounding the genome (capsa)
Virus particles are metastable -> must be stable to protect the genome, must be unstable and fall
apart on infection
3 basic virus structures
7 types of genomes but only 3 types of particle structure
-> helical, isocahedral, complex
Symmetry is the key to build virus particles
1
, Watson and Crick seminal observations:
They noticed that most virus particles were spherical or rod-shaped
Theory of genetic economy: as virus genomes are small, particles would be built with many
copies of a few proteins
Identical protein subunits are distributed with helical symmetry or rod-shaped/filamentous
viruses
Icosahedral symmetry for spherical viruses
Complex bacteriophage structures combine helical and icosahedral symmetries
Rule 1: each subunit had identical bonding contacts with its neighbours: repeated interaction of
chemically complementary surfaces at subunit interfaces naturally leads to symmetric arrangement
-> the more subunits, the larger the capsid
Rule 2: these bonding contacts are non-covalent: they are reversible
Virus particles are metastable
The stable structure is created by symmetric arrangement of many identical proteins to
provide maximal contact
Because the structure is not permenantly bounded together is can become unstable and can
be taken apard or lossened on infection to release or expose the viral genome
Many capsid proteins are self assembling in VLP = virus like particles
1. Helical symmetry
One single protein that coats the viral DNA
Enveloped RNA viruses with ss(-)RNA and helical capsids
o Filoviridae (ebola)
o Orthomyxoviridae (influenza)
o Rhabdoviridae (rabies)
o Paramycoviridae (measles virus, mumps virus)
DsDNA viruses of archaea
ssDNA viruses of bacteria
- and + RNA viruses of plants (non-enveloped)
2
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