Viruses

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.

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

Shape & Size of Viruses Viruses vary widely in

shape. Vary greatly in size.

Much smaller than bacteria.

Structure of Viruses

2 ComponentsOuter Coat

Made of proteinsProtects the virusHelps the virus attach to

the surface of the host cell

Inner Core of Genetic Material

Either DNA or RNA

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.

Lytic vs. Lysogenic Viruses Lytic “Active” Virus

Virus immediately takes over cell’s functions and new viruses are rapidly produced

Eventually the cell bursts.

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.

Viral Diseases

Preventing Infectious Diseases

VaccineA 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.

Summary QuestionsExplain 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.