Viruses1-1-1

1 – main characteristic1 – surprising fact1 – question

Viruses

What’s a Virus?1. Viruses are tiny particles that can invade living cells. Because viruses are not cells they are non-living and can not perform all the functions of living cells.

For example, they cannot take in food or get rid of wastes. In fact, about the only life function that viruses share with cells is reproduction.

2. Viruses can only reproduce (multiply) when they are inside a living cell.

3. The organism that a virus enters is called the host. A host is a living organism that provides a source of energy for a virus or organism.

4. Organisms that live on or in a host and cause harm to the host are called parasites.

• Almost all viruses act like parasites because they destroy the cells in which they multiply.

When you have a cold, are you the host or a parasite?

How Viruses Multiply

The Structure of a Virus

5. A virus is a piece of genetic material (DNA or RNA) covered by a protein called the

protein coat, that infects and reproduces only in a living cell.

Genetic material (DNA or RNA)

Protein coat

The Size of a Virus

6. Viruses are so small that they can only be seen with very powerful microscopes. They are

about 100X smaller than a typical bacterium. They are measured in nanometers (nm) which

are 1 billionth of a meter! (1/1,000,000,000; 1/109)

Virus

How Big is a ….?

Viruses come in many sizes and many shapes.

Viruses are not included in the classification system we studied and are not named using binomial nomenclature.

Can you tell me why?

Viruses are often named for the diseases they cause or the organ or organism they infect.

rabies virus – causes the disease rabies

adenovirus – infects adenoid tissue bacteriophage – is a virus

that infects bacteria

Viral Diseases

7. Viruses can cause diseases in plants, animals, fungi, bacteria and protists.

8. There are no antibiotics to cure viral diseases. But some viral diseases can be prevented by vaccines.

A vaccine is made from damaged virus particles that can’t cause disease anymore.

9. Edward Jenner, an English doctor, is credited with developing a vaccine in 1796. Jenner developed a vaccine for smallpox, a disease that was greatly feared, even into the twentieth century.

Jenner noticed that people who milked cows and came down with a disease called coxpox didn’t get smallpox. He prepared a vaccine from the sores of milkmaids who had cowpox. When he injected it into healthy people, the cowpox vaccine seemed to protect them from smallpox.

Viral Diseases in Humans

Disease Affected Body Part

Vaccine

Aids Immune system no

Chicken pox Skin yes

Common cold Respiratory system no

Influenza or flu Respiratory system yes

Measles Skin yes

Mumps Salivary glands yes

Polio Nervous system yes

Rabies Nervous system yes

smallpox Skin yes

The good thing about viruses is…10.Viruses are used in gene therapy.

Scientists take advantage of a virus’s ability to enter a host cell. They add important genetic material to a virus and then use the virus as a messenger service to deliver the genetic material to the cells that need it.

This technique has been used successfully for treating cystic fibrosis. Researchers are hoping to use similar techniques for sickle-cell anemia and cancer.

Viruses1-1-1

1 – main characteristic1 – surprising fact1 – question