Chapter 20.1 - Viruses

Part 1 – Virus Structure and Function

The Discovery of Viruses

Scientists were looking for the cause of a disease that was

infecting TOBACCO plants.Causing tobacco mosaic

disease.

The Experiment

Filter a solution that causes the disease through a small filter that bacteria cannot get through.

The Results

The filtered solution can still infect the tobacco plant.

The Conclusion

The disease was caused by something smaller than a bacteria. They called it a virus.

The Discovery

1935—Wendell Stanley discovered the structure of a virus and proved that they are NOT a

LIVING ORGANISM. 1946 Nobel Prize

winner. Extensive virus work..proved that they cause cancer.

What is a Virus

Complex, submicroscopic, organic particle. (20 nm, have carbon)

Not cellular, no cell parts. Do not carry out life functions on

their own. Reproduce only inside a living cell

(host cell)

What is a Virus

Parasitic (live off others)Disrupts the lives of the

cells they invadeFound in air, soil, and water

Structure of a virus capsid

Nucleic acid

Tail

filaments

Influenza

Small pox

bacteriophage

Ebola

West Nile

HIV

Hepatitis C

Structure of a Virus

A virus is a particle made up of a

nucleic acid core (either DNA

or RNA) and an outer protein coat called a capsid.

Some viruses also have an extra

outer layer called an envelope.

Role of Viruses

Most viruses are pathogens—

disease causing agents.Small pox, chicken pox, cold sores,

warts, AIDS, rabies, mumps, flu, measles, some forms of cancer and the common cold are caused by viruses.

How does the body handle viruses?

It is the job of the immune system to

fight diseases in the body. Your skin is one of the most important organs in this system because it keeps pathogens out of your body.

Once a virus is in your body, your main

defense is white blood cells. These cells are specialized to fight pathogens.

There are 2 main types of white blood

cells. T cells and B cells. B cells are normally more important for fighting viruses. Once a virus has entered your body, your B cells produce proteins called antibodies that will remember the virus and fight it off if the same virus enters your body again. This means that you normally never get the same viral infection twice.

Why do people have more than one cold or the flu more than once?

These viruses mutate quickly so your body doesn’t recognize them as the same thing.

(there are more than 200 strains of the common cold)

Vaccine

Substance prepared from

inactive or weak viruses that cause your body to react and produce antibodies without making you sick.

The HIV virus

HIV, the virus that causes AIDS, is in a class of viruses called retroviruses. These

viruses have RNA as their nucleic acid.

How do retroviruses reproduce?

They have a way to convert RNA to DNA.

The DNA is copied by the cells they invade.

HIV’s structure

HIV attacks your body’s T cells

Virus docks by matching receptor shapes on host cell surface.

HIV

Host cell

Matches the receptor on host

Because HIV mutates very quickly, it is difficult to cure.