Download Viral Structure - Chapman @ Norquay School

A Brief Look at the Structure of Viruses
Mr. Chapman
Biology 20

Viruses are much smaller than plant and
animal cells, and also much smaller than
bacterial.

Viruses range in size from 18 – 300 nm. Note
that 1 nanometre = 1 x 10-9 m.

A virus is simply made of genetic material
(either RNA or DNA) surrounded by a protein
shell called a capsid.

A single viral particle is called a virion.

Capsids (the protein structure on the outside
of the virus) are different shapes for different
viruses, and some are covered by a lipid
(a.k.a. Fat) envelope.

The lipid envelope is the protective outer coat
of a virus, from which spiky structures from
proteins or sugars sometimes stick out.

A virus is called a naked virus when it consists
of only the genetic material surrounded by a
capsid (no lipid envelope).

In some viruses, capsids form a 20-sided
polyhedron.

Other viruses are rod-like, and some strandlike viruses are shaped in coils, like a spring or
a helix.

Unlike prokaryotes and eukaryotes, viruses
have DNA or RNA, but never both.

The structure and shape of particular viruses
are very important.

A virus can only infect certain hosts, and it
identifies its hosts by fitting its surface
proteins to receptor molecules on the
surface of the host cell.

The system is like a lock and key, and viruses
need the correct key to infect a particular cell.
Believe it or not, the answer is not clear.

Unlike other types of cells, a virus really has no
structure to maintain at all.

Viruses don’t eat, excrete, use energy, or require
oxygen at all. They don’t have organelles, either
In fact, they do almost nothing that living
organisms do – except reproduce.

Even so, a virus can only reproduce after it has
infected a host cell.

What are the three main components of a
typical virus? Which one of these components is
a naked virus missing?

How does the size of a virus compare to that of a
plant or animal cell?

Why are the structures protruding from the lipid
envelope important for bonding to host cells?

Why is it unclear as to whether or not a virus is
alive?
Complete the rest of the class by reading section 18.2 of the Biology
textbook, and complete questions 1 – 4 on page 551.