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Week 139 – Influenza – Introduction to Viruses
Introduction to Viruses – Structure
•

The hierarchical viral structure is as follows:

− Naked virus – central genome (ss/ds RNA or DNA) è Capsid (composed of
capsomeres)
− Enveloped virus – as above + lipid bilayer membrane punctuated with
glycoprotein spikes

•

The nucleocapsid – has symmetry that can be:

− Icosahedral (i
...
DNA or RNA genomes) – herpes simplex, poliovirus &
parvovirus
− Helical (i
...
RNA genomes) – rabies & measles virus
− Complex (i
...
mostly RNA genomes) – bacteriophage (i
...
bacteria-infecting
virus) & influenza
Introduction to Viruses – Viral Lifecycle
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The viral lifecycle includes:

1
...

3
...

5
...

7
...
e
...
e
...


Introduction to Viruses – Viral Lifecycle – Penetration & Uncoating
•

Penetration can occur as follows:

1
...
e
...

2
...
e
...
This process is pHindependent and is utilised by measles, mumps & HIV
...
Receptor-mediated endocytosis (i
...
naked & enveloped viruses) – involves
attachment & endocytosis of the virion to form an intracellular endosome
...

•

Uncoating – is rupturing of the protein coat or viral capsid and exposure of
the viral genome within the host cell
...
DNA viruses – can use host DNA-dependent RNA polymerase to produce
mRNA
...
Positive sense ssRNA viruses – have RNA analogous to mRNA, which is
translated directly into viral proteins (i
...
RNA-dependent DNA polymerase)
...
Negative sense ssRNA & +/- sense dsRNA – use viral RNA-dependent RNA
polymerase to produce mRNA
...
Positive sense ssRNA (retro-) viruses – use viral RNA-dependent DNA
polymerase to produce dsDNA, which is incorporated into the host cell
genome by viral integrase
...

•

Viral genome replication can occur as follows:

1
...

2
...

3
...

4
...


DNA viruses
(exc
...

RNA viruses
replicate in the
nucleus

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