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Viruses
Are they alive ?
What is a Virus?
A non – living, infectious particle made only
of a strand of DNA or RNA surrounded by a
protein coat. This protein coat is known as
a capsid.
Why would some
scientists debate
that a virus was
living?
Why are viruses considered non-living?
Viruses can not reproduce on
their own. A host cell is needed
for a virus to reproduce and make
proteins.
A virus is referred to as a pathogen.
A pathogen is any organism or
nonliving particle that can cause an
infectious disease.
Viroids and prions are pathogens as
well.
and use your book !!
Define:
1) Viroid:
2) Prion:
Mad Cow Disease
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1) What is mad cow disease?
2) What is the medical name for mad cow disease?
3) What is the human form of mad cow disease?
4) How can humans get vCJD?
5) How is the United States preventing the spread of vCJD?
6) What is one theory of how mad cow disease is caused?
7) How are healthy cows infected by cows with the disease?
8) When was the first case of vCJD reported?
9) How did the United States avoid spreading vCJD in December
2003?
• 10) List the symptoms of vCJD.
• 11) How is a case of vCJD confirmed?
• 12) Since there is no cure for vCJD, how are patients treated?
Mad Cow Disease News Clip
http://www.youtube.com/watch?v=
VgB9sg5dy8w
The Structure of a Virus
Surrounded by a protein coat called the capsid.
Capsids have many different shapes.
Each type of virus can infect only certain hosts.
For example, a bacteriophage is a virus that only
infects bacteria.
The virus uses its capsid to attach to the host cell ,
like a key fitting a lock.
There are 3 viral structures: bacteriophage, tobacco
mossaic, and influenza.
How do Viruses make us sick?
• Viruses cause 2 types of infections. Use
your book and write the analogies
used to describe each. Refer to pg 549
2 Types of Viral Infection
• Lytic Infection
• Lysogenic Infection
An infection pathway in
which the host cell bursts
releasing the new viral
offspring into the host’s
system. This infection does
not take long for symptoms
to occur.
The virus combines its DNA
into the host cell’s DNA
forming a prophage. This
infection can lie dormant for
a period of time before
symptons occur.
Example: Cold Virus & Flu
Example: AIDS, Herpes,
Chicken Pox
When a host’s cell bursts, the term used is Lyse.
Cell Lyse
lyse
Animated BIO