Viruses What are viruses How do viruses cause

Viruses • What are viruses? • How do viruses cause infection?

What are infectious agents? Viruses – made of a nucleic acid molecule (DNA or RNA) surrounded by a protein coat (Not living) ◦ Example: influenza Viroids – made of single-stranded RNA without a protein coat (Not living) ◦ Only infect plants Prions – made of proteins that cause other proteins to fold incorrectly (Not living) ◦ Destroy nervous tissue ◦ Example: mad cow disease Bacteria – prokaryotes (Living)

Virus Structure Made of genetic material surrounded by protein coat (capsid) ◦ Capsid can be surrounded by a lipid bilayer

Types of Viruses Bacteriophages ◦ Viruses that infect bacteria ◦ Inject their genetic material into host cell Viruses that infect eukaryotes ◦ Can be directly injected into the host cell Example: HIV ◦ Can be taken into host by endocytosis Example: Influenza

Lytic Infection Virus attaches to host cell Injects genetic material Viral genetic material destroys host cell’s DNA Uses host cells proteins to make new viruses New viruses burst (lyse) out of host cell

Lysogenic Infection Virus attaches to host cell Injects genetic material Viral genetic material incorporates itself into host cell DNA (prophage or provirus) As host cell DNA is replicated, viral genetic material is too At some point, moves into lytic cycle to release new viruses