VirusesViruses

Are they living?

Video Clip: United Streaming

• Watch this Video Clip from United Streaming as an introduction to Viruses– Introduction to Viruses_Discovery

School_(2:58)

Make a Comparison

• THINK! - How are computer viruses similar to viruses that infect your body?

– A computer virus uses your computer’s resources to do its dirty work

– A virus that infects living organisms does the same thing. It takes over the cells of the living organism.

Are Viruses Considered Living?

• Viruses DO NOT have all six characteristics of life.

• Viruses can’t reproduce on their own. They need living cells or hosts (living things that harbor viruses).

• For this reason, viruses are considered non-living.

• We refer to viruses as parasites .

• THINK! – What is a parasite?– something that lives inside an organism and

harms it.

How Does a Virus Enter a Host?

Flu Attack! How A virus Invades your Body!http://www.youtube.com/watch?

v=Rpj0emEGShQ&noredirect=1

As you watch think of the following:

1. How does a virus enter your cells?

2. What is a virus made of?

3. How do you defend against it?

The proteins on virus match proteins on your cell (key and lock)

Proteins and Genetic Material

Your Body has an immune system

How Does a Virus Enter a Host?

Structure of Viruses

• Size– Viruses are extremely small– An electron microscope is needed to see them

• Shape– Viruses can be round, rod-shaped, or cubed

• Structure– 1. Protein coat

• Thin covering which protects the virus particle.

• It is studded with proteins that are recognized by the host cell. In this way, a virus can trick a cell into letting it inside

– 2. Genetic material• Viruses do not contain a nucleus. • However, a virus does contain a core of

genetic material (DNA or RNA) which controls the particle.

Can you find the 2 parts to each virus?

Life Cycle of A Virus

• Viruses multiply using the following steps:

– 1. Virus attaches to its host.

– 2. Virus injects its genetic material inside the host cell.

– 3. The viral genetic material takes over and viral parts are made.

– 4. These viral parts assemble into viruses.

– 5. The virus particles burst out of the cell and the dead host cell is left behind.

Active Viral Life Cycle

Go online: www.phschool.com use Web Code cep-1021

Defending Against Viruses

• Vaccines

– Vaccines are made from weakened varieties of a virus.

– They work by stimulating your immune system to create antibodies against the virus.

• THINK! – Why don’t we have a vaccine for every virus?

– Some viruses like the common cold virus, flu, and HIV mutate (change) rapidly.

– Even if you were vaccinated your body would not be able to defend itself against the new and improved strain.

Vaccines & How They Work

• Watch the segment from PBS Program Rx for Survival titled “Vaccines & How They Work”– http://www.pbs.org/wgbh/

rxforsurvival/series/video/index.html

– Pay attention to the historical significance of the scientific discoveries made!