4C Viruses

• NONLIVING• Contain either DNA or RNA

(but NEVER Both)

VIRUS

Why is a virus considered non-living?

• They cannot replicate on their own (without a host cell)• They cannot obtain and use energy• They cannot respond to the

environment

What a virus does

It invades a cell.It turns the cell into a virus making

factory until it no longer needs the cell.

It then destroys the cell releasing new viruses to continue the cycle.

How does a virus replicate?

Virus injects it’s genetic info into a host cell. Host cell then “replicates” viral DNA

to makes new viruses

How do they replicate?(replicate means to make more)

LYTIC CYCLE

Lysogenic CycleWait for animation

LYTIC CYCLE

• destroys host cell in a short amount of time

LYSOGENIC CYCLE

• takes longer to destroy host cell

Both Cycles Together

Types of Viruses

• Adenovirus• Retrovirus• Bacteriophage

Adenovirus

• any of a group of DNA viruses first discovered in adenoid tissue, most of which cause respiratory diseases

Retroviruses• Made of RNA• Inject their RNA into

the host cell• Host cell makes it into DNA• Viral DNA joins the host DNA• Viral DNA pirates the cell and forces the cell

to make new viral RNA and new viruses

HIV is a retrovirus

Bacteriophage

Virus that

attacks bacteria

Common Viral Diseases

• Rhinoviruses cause the common cold• HPV (Human papillomavirus) can cause cervical

cancer in women• Herpes simplex viruses cause mouth and/or genital

sores, lesions, and ulcers.• Influenza viruses cause the flu• HIV (Human Immunodeficiency Virus) causes AIDS

and weakens the immune system

Rabies

H1N1

Plant Viruses

How is a disease caused by a virus?

• New viruses made inside BURST out of and destroy host cell

• When your cells die your health is affected

Controlling Viruses

• Antibiotics DO NOT work on viruses.• Most human viral infections can be

fought off by the immune system—boost the immune system with lots of water and rest.

How does a VACCINE work?• Vaccines stimulate the immune

system to create antibodies that recognize a certain virus… • Vaccines inject a small amount of

the virus into your system.

How do vaccines work?• The body then builds antibodies to fight that

specific virus.• Antibodies remember that virus in the future

in case you are exposed to that virus again. • These antibodies patrol your body and if

they recognize that virus…they call in reinforcements and your immune system goes to battle!

Compare viruses to living cellsWhat do they have

in common?

They have DNA & RNA and

They both change over time