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Viruses
Is a virus living like a cell?
Achoo!!

Sneezing is an involuntary
action that aids the body by
clearing congestion within
the nose. But sneezing also
spreads viruses.
1.
What happens if a virus
enters your body? What are
some symptoms?
2.
What can you do to limit the
spread of viruses?
What is a Virus?

Is it living or nonliving?


NON-LIVING
Why would we think
it’s living?


Has DNA
Can Reproduce
What is a Virus?

A strand of DNA
surrounded by a
protein coat.
Virus Multiplication

Viruses can make copies of themselves only inside a
living host cell.
Virus Multiplication


Active viruses – make the host cell create new viruses,
which kills the host cell.
Latent viruses – hide in the host cell without destroying it.


Virus hereditary material becomes part of the host cell hereditary
material.
Latent viruses can become active and then destroy the host cells.
I’ll hide out! They’ll
never find me!
Effects on Organisms

Most viruses infect only specific kinds of cells.

Viruses are often carried to the host through the air.

The virus and host cell must fit together exactly to
begin a viral infection.
Effects on Organisms

Bacteriophages attach to bacteria and inject their
hereditary material.
Fighting Viruses


Vaccines – weakened virus particles that allow the
host to fight some diseases.
Treating viral diseases




Antibiotics are not effective treatments for viral
infections.
Infected cells sometimes produce interferons which are
proteins that can protect noninfected cells.
Antiviral drugs often have adverse side effects, limiting
their use.
Public health measures can prevent or slow disease.
Research

Gene therapy uses viruses to replace defective
cell hereditary material with normal cell
hereditary material.
Viral Reproduction
1. The virus attaches to
a specific host cell.
Viral Reproduction
2. The virus’ DNA
enters the host cell.
Viral Reproduction
3. The DNA of the
virus causes the cell to
make copies of itself!
Viral Reproduction
4. New viruses form
inside the host cell.
Viral Reproduction
5. New viruses are
released as the host cell
bursts open and is
destroyed.