1. Viruses
Chapter 2 Ce!s
Section 3

2. What are viruses???
cold sores the flu measles AIDS
virus
•nonliving particle
•strand of hereditary material surrounded by a protein
coating
•no nucleus or other organelles
•no cell membrane
•can have many shapes
•too small to be seen with the light microscope

3. how do viruses multiply
•all viruses can make copies of themselves
•they can’t do that without the help of a living cell
•the living cell is called a host cell
•crystallized viruses can be stored for years. Then, if
they enter an organism, they can multiply quickly.
•once a virus is in a host cell, the virus can act in 1 of 2
ways:
•be active
•become latent (inactive)

4. active viruses
When a virus enters a cell and is active, it causes the host cell to
make new viruses. This process destroys the host cell.
Steps that occur:
virus aaches to a specific host cell
virus’s hereditary material enters the host cell
hereditary material causes the cell to make viral hereditary
material and proteins
new viruses form inside the host cell
new viruses are released as host cell bursts open and is
destroyed

7. latent viruses
virus enters the cell
its hereditary material can become part of the cell’s hereditary
material
does not immediately make new viruses or destroy the cell
as host cell reproduces, the viral DNA is copied
can be latent for years
certain conditions, whether inside or outside your body, cause
the latent virus to become an active virus

9. example:
COLD SORE
a latent virus in the body has become active
cold sore is a sign that the virus is active and destroying
cells in your lip
when the cold sore goes away, the virus has become latent
again
virus is still in your body’s cells, but it is “hiding” and doing
no apparent harm

10. how do viruses affect organisms?
Who can viruses aack?
animals, plants, fungi, protists, bacteria
Some viruses only infect only specific kinds of cells...
Some viruses are limited to one host species (ie: potato
leafroll virus) or to one type of tissue.
Some can affect a broad range of hosts. Rabies, for
example, can infect humans and many animals.
The virus and the place it aaches to the surface on the host
cell must fit together exactly. Because of this, they usually
only aack one type of cell.

12. How do viruses move?
They cannot move by themselves. They reach a host’s
body by being carried by the wind or by being inhaled.

13. fighting
viruses
We fight viruses by geing VACCINES
they are used to prevent diseases
made form weakened virus particles that can’t cause
disease anymore
vaccines have been used to prevent many diseases, such as:
measles, mumps, smallpox, chicken pox, polio, rabies, swine
flu

14. first vaccine
Edward Jenner is credited with developing the
first vaccine in 1796.
He developed a vaccine for smallpox, a disease
that was still feared in the early twentieth
century.
Jenner noticed that people who got a disease
called cowpox didn’t get smallpox.
Jenner didn’t know he was fighting a virus

16. treating viral diseases
WHAT YOUR BODY DOES ON ITS OWN: make interferons.
What are interferons???
proteins that are produced rapidly by virus-infected cells
they move to non-infected cells, causing them to produce
protective substances.
MEDICINE THAT CAN HELP: Antiviral drugs
Antiviral drugs can be given to infected patients to help fight a
virus.
Some are effective, but some have adverse side effects.
Antibiotics treat bacterial infections but not viral diseases

18. preventing viral diseases
Public health measures for preventing viral diseases
includes:
Vaccinating people
Improving sanitary conditions
Quarantining patients
Controlling animals that spread disease

19. research with viruses
Through research, scientists are discovering helpful uses for
some viruses.
Gene therapy substitutes normal hereditary material for
a cell’s defective hereditary material.
The normal material is enclosed in viruses that “infect”
targeted cells.
The new hereditary material replaces the defective hereditary
material.
Using gene therapy, scientists hope to help people with genetic
disorders and find a cure for cancer.