Structure
of
Viruses
The intact virus unit or infectious particle is called the virion. Each virion consists of a nucleic acid core surrounded by a protein coat (capsid) to from the nucleocapsid.
The nucleocapsid may be naked or may be surrounded by a loose membranous envelope. It is composed of a number of subunits called capsomeres.
The capsid protects the nucleic acid core against the action of nucleases.
Viruses
occur
in
three
main
shapes,
spherical
(actually
polyhedral),
helical
(cylindrical
or
rod
like)
and
complex.
Polyhedral and helical viruses may have naked capsids, or the caps ids may be covered by envelopes.
