Viruses
The latin word for poison!!!
A Virus

Nonliving particle cosisting of a core of
hereditary material surrounded by a protein
coat.
 Does not grow
 Does not respond
 Does not eat
 Only reproduces
 Can reproduce only inside a living cell (host
cell)
Viruses
 Some
can be made into crystals and
stored in a jar for years.
 If opened, the virus can enter an
organism (host), quickly reproduce, and
cause new infections.
 Causes damage to the organism
Classifying Viruses
 Viruses
come in a variety of shapes due
to their protein covering.
 They are responsible for many
diseases.
 They are classified by shape, the kind of
hereditary material they have, the kind
of organisms they infect, and their
method of reproduction.
Naming Viruses
 Viruses
are often named after the
disease they cause.
 Ex: polio virus……causes polio disease
 Also named after the organ or tissue
they infect.
 Ex: adenovirus…infects the adenoid
tissues.
The T4 Virus
 Also
called a bacteriophage
 Type of virus that infects bacteria.
 Many sided head attached to a tail.
 Injects its hereditary material into the
cell through the tail, much like a
hypodermic needle.
T4 Bacteriophage
What do viruses do?
 Once
inside a host cell, a virus can do 1
of 2 things.
 1. Be active (Lytic)
 2. Be latent: or be an inactive part of
the cell for a while. (Lysogenic)
The Active Phase (overview)
The Active Virus (Step 1)
Attach: a specific virus attaches to the
surface of a specific bacterial cell.
The Active Virus (Step 2)
Invade: Hereditary material of the virus
injects itself into the bacterial cell.
The Active Virus (step 3)
Copy: Viral heredity material takes control of the
bacterial cell and the cell begins to make new virus
particles.
The Active Virus (step 4)
Release: Cell bursts open and hundreds of new
virus particles are released. New particles go on to
infect other cells.
The Latent Virus
 The
latent virus enters the cell and
becomes part of the cells hereditary
material without immediately destroying
the cell or making new viruses.
 May “hide” inside cells for many years.
 May become active at any time.
The Latent Virus (overview)
Latent Virus (Step 1)
Specific virus attaches to the surface of a specific bacterial cell.
Hereditary mateial of the virus injects itself into the cell.
Latent Virus (Step 2)
Virus becomes part of the bacterial cell’s chromosomes.
Latent Virus (Step 3)
Bacterial cell divides.
Latent Virus (Step 4)
Virus leaves chromosome and becomes active.
Latent Virus (Step 5)
New viruses are made.
Latent Virus (Step 6)
Bacterial cell breaks open and releases the viruses destroying the
host bacterial cell.
Latent Virus Example

Cold Sore:
 From latent phase to the active phase
 Virus enters the cell is remains latent.
 Stress, too much sun or cold makes the virus
become active.
 Sores become abundant.
 Sores disappear; virus becomes latent again.
 Still present, just not active.
Viral Diseases
 May
cause disease in plants, animals,
fungi, bacteria, and protists.
 No antibiotic medications to cure
viruses.
 Can be prevented by vaccines.
 Vaccines made from damaged virus that
can no longer cause disease.
Vaccine Example

Edward Jenner
 Developed vaccine in 1796 for smallpox.
 Smallpox was a greatly feared disease.
 Prepared the vaccine from using some of the
samples taken from the sores of the
milkmaids that had cowpox.
 Injected the material into healthy people.
 Protected them against the smallpox virus.
The End