1. Viruses

2. What is a Virus?
A microscopic particle that gets inside a cell and often destroys the cell.
Examples:
Common cold
Flu
Acquired Immune Deficiency Syndrome (AIDS)

3. Viral Characteristics
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?

4. Non-Living Characteristics Living Characteristics
Are Viruses Living?
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
Living Characteristics
Has genetic material and proteins

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

6. Shapes of Viruses Crystals Spheres Cylinders Spacecraft
Example: The polio virus
Spheres
Example: Influenza viruses and HIV
Cylinders
Example: Tobacco mosaic virus
Spacecraft
Example: Viruses that attack bacteria

7. Structure 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

8. How do viruses make more of themselves?
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.

9. The Lytic Cycle 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.

11. The Lysogenic 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.

12. Treating a Virus Antibiotic? Fluids Antiviral medications
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

13. Preventing Viral Infections
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.