1. Viruses

2. Characteristics of Viruses
A small, nonliving particle that invades and then reproduces inside a living cell.
Nonliving because…
Viruses are not cells.
Do not use energy to grow or to respond to their surroundings.
Cannot make food, take in food, or produce wastes.
Act as a parasite
Obtain energy from host and may cause harm to their host.

3. Naming Viruses Don’t use binomial nomenclature (nonliving)
Variety of names.
Ex. Tobacco mosaic virus, Ebola, Epstein-Barr

4. Shape & Size of Viruses Viruses vary widely in shape.
Vary greatly in size.
Much smaller than bacteria.

5. Structure of Viruses 2 Components Outer Coat
Made of proteins
Protects the virus
Helps the virus attach to the surface of the host cell
Inner Core of Genetic Material
Either DNA or RNA

6. How Viruses Multiply Basic Mechanism
Attachment
Virus enters cell
Virus’s genetic material takes over the cell’s functions
Genetic material directs the cell to produce the virus’s proteins and genetic material
Proteins and genetic materials are then assembled into new viruses
KEY DIFFERENCE: Some viruses take over the cell’s function immediately while others wait for awhile.

7. Lytic vs. Lysogenic Viruses
Lytic “Active” Virus
Virus immediately takes over cell’s functions and new viruses are rapidly produced
Eventually the cell bursts.

8. Lysogenic Cycle
Instead of going into action to make more viruses, the virus’s DNA becomes part of the cell’s genetic material.
Does not affect cell’s function for awhile.
After a period of time, the cell will suddenly enter the lytic cycle.

10. Viral Diseases

11. Preventing Infectious Diseases
Vaccine
A substance that stimulates the body to produce chemicals that destroy viruses or bacteria.
May be made from dead or altered viruses or bacteria.
Does not cause the disease but activates the body’s natural defenses and effectively puts the body “on alert” for possible virus or bacteria invasion.

12. Summary Questions Explain why viruses are considered nonliving.
Describe the basic structure of a virus.
Describe how viruses multiply.
You have a case of the flu. A friend recommends a new treatment advertised in a magazine. The ad states that the treatment works by “deactivating the virus’s nucleus so it can’t reproduce.” Could this treatment cure you? Explain.