Viruses

A microscopic particle that gets inside a cell and often destroys the cell.

Examples:◦ Common cold◦ Flu◦ Acquired Immune Deficiency Syndrome (AIDS)

What is a Virus?

Small◦ Smaller than the smallest bacteria◦ About 5 billion virus particles could fit into a single

drop of blood. Can change rapidly

◦ Think about the flu vaccine…why can’t you simply get a flu shot one time and be vaccinated for life?

Viral Characteristics

Living Characteristi

cs

• Has genetic material and proteins

Non-Living Characteristics• Doesn’t eat (metabolism)• Doesn’t grow• Doesn’t use oxygen• Can only reproduce inside a

living cell that serves as a host• Using the host cell as a

factory, the virus forces the cell to make a virus rather than a healthy new cell.

• Can only function inside of a host

Are Viruses Living?

Viruses can be grouped by their shape, the type of disease they cause, or the kind of genetic material they contain.

Classification of Viruses

Crystals◦ Example: The polio virus

Spheres◦ Example: Influenza viruses and HIV

Cylinders◦ Example: Tobacco mosaic virus

Spacecraft◦ Example: Viruses that attack bacteria

Shapes of Viruses

All viruses are made of genetic material inside a protein coat.◦ The coat protects the genetic material and helps a

virus enter a cell.◦ Many viruses have a protein coat that matches the

characteristics of their specific host. The genetic material is either DNA or RNA

◦ Both of these contain information for making proteins Viruses that cause warts and chicken pox contain DNA Viruses that cause colds, the flu, and HIV contain RNA

Structure of Viruses

Viruses attack living cells and turn them into virus factories using the lytic cycle.

Some viruses don’t enter directly into the lytic cycle but instead go into the lysogenic cycle which is then followed by the lytic cycle.

How do viruses make more of themselves?

The virus finds and joins itself to a host cell. The virus enters the cell or the virus’s

genetic material is injected into the cell. Once the virus’s genes are inside, they take

over the direction of the host cell and turn it into a virus factory.

The new viruses break out of the host cell, which kills the host cell.

The cycle begins again.

The Lytic Cycle

The virus puts its genetic material into the cell but new viruses are not made right away.

Each new cell gets a copy of the viral genetic material when the host cell divides.

The genes stay inactive until the necessary amounts or conditions occur and then they become active.

Once the genes are active, the cells enters the lytic cycle.

The Lysogenic Cycle

Antibiotic?◦ Do not kill viruses

Fluids◦ Rest and drinking extra fluids is a way to help

your body fight the infection. Antiviral medications

◦ Many stop viruses from replicating and eventually the virus dies out

Treating a Virus

Vaccinations◦ Give the immune system a head start in fighting

off viruses Good hygiene

◦ Washing hands regularly, avoid going to work/school when you have a fever, etc.

Preventing Viral Infections