Download Viruses Living or Not

Viruses
Living or Not
???????
Characteristics of Viruses


Among the smallest
biological particles
that are capable of
causing diseases in
living organisms
Constructed of
compounds
associated with cells
Not Considered Living



A virus is not a
bacteria, fungus,
protist, plant or
animal.
They can not carry out
cellular functions.
A virus can not
replicate without
infecting cells and then
using the organelles
and enzymes of the
cells of the host.
Some scientists argue that
viruses are considered living.
What characteristics of life do
viruses exhibit that could
support this theory?
Be prepared to share your answer…
A Virus Has Two Essential Features

A Nucleic Acid
 DNA
or
 RNA
 But

not both
A Capsid – a
protein coat
surrounding the
nucleic acid.

Some may have a
membrane like
structure outside
the capsid called an
envelop

Examples:
Influenza
 Chickenpox
 Herpes-simplex
 HIV

Viral Shape


The shape of the virus is
determined by either its
capsid or its nucleic acid
Two examples of shape
Icosahedron has 20
trianglular faces -- herpes
simplex, chicken pox and
polio
 Helix is a spiral shape
( like DNA) -- rabies,
measles and tobacco
mosaic virus

How Do Viruses reproduce?
 REPLICATION
Steps of Viral Replication
1. The virus attaches to a
host cell
 2.
The virus
injects its
information into
the host cell



3. Viral parts are reproduced by using
the Host cell’s DNA
4. Viral parts are assembled to create
new viruses.
5. Viruses fill host cell. Cell bursts
(Lysis) to release new cells.
How do we remember this????

Create a pneumonic device to remember
the steps of Viral Replication.
Basic Virus Structure
Genetic
material
Head/
Capsid
Tail fibers