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viral properties
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notes on viral properties including types of virus, virus structure, virus genomes, stages of an infection
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1Hull York Medical School
Viral properties
Viruses are smaller than anything from the bacterial world – they are nanometers
small – we can only see them with electron micrograms
Shapes include – filamentous, icosahedral, spherical
Icosahedron – very symmetrical – has 20 faces – proteins come together to make the
virus particle in this shape
Viruses are outside of the domains of life due to their need for a host to replicate
Obligate intracellular parasites – use hosts and depend on the machinery of the host
to replicate
Cannot make energy or nuceic acids independent of their host
Replication is by self-assembly of individual parts
Genomes are either DNA or RNA
As it is intracellular it must be infections to ‘live’
Must be able to use and subvert the hosts processes to produce their components
Viral components self-assemble
Virus structure
o Nucleocapsid – has a nucleic acid such as RNA or DNA contain in a capsule
o Virion – the infectious part – non-enveloped (naked) is the nucleocapsid –
enveloped – nucleocapsid plus envelope – enveloped have glycoproteins and
a capsid
Enveloped virus example – Influenza virus – spike proteins H and N – susceptible to
mutation and recombination – new strains can cause pandemics or epidemics
Naked virus – norovirus – many catch this in the winter – spread through water or
food which has been contaminated
Being naked or enveloped has an impact on the stability – naked spreads more easily
as it is more stable – can survive in many environments – enveloped viruses must
stay wet and are very sensitive to detergents. They are very large and must spread
through droplets and does not need to kill a cell to spread.
Infectious dose – the lower the number the more infectious
Can classify based on what we see but overall that is fairly useless – they are
classified by the identity and the polarity of the nucleic acid and strategy of their
replication
DNA and RNA are opposite strand – RNA is always single stranded – mRNA is + a
copy of this strand is the – strand
DNA, RNA or RNA-DNA viruses – double or single stranded
How a new virus particle is made – needs to have new viral proteins so you need
mRNA and a copy of the genome
Virus genomes must code for proteins for all parts not in the host cells – proteins for
viral particle, enzymes for replication and what is needed to interfere with the host
immune defence or aid infection
Must have mRNA to create a virus – you will need enzymes for double stranded RNA
– this is a virus specific process
How is the genome replicated? RNA, DNA or retrovirus?
You cannot copy positive to positive it needs to go from negative to positive
Rabies – negative strand which needs to make a positive copy to go back to negative
- -RNA enters cell and copy is made to +RNA – proteins allow genome copying
Stages of the infectious cycle:
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