Viruses

Evolution of Virus Alive or Not Biologically inert Unable to replicate genes Unable to regenerate ATP probably evolved as bits of cellular nucleic acid

Structural Component of Virus small infectious particles nucleic acid Double or single stranded DNA Double or single stranded RNA Single circular molecule or linear Capsid Protein shell some cases, a membranous envelope Made from membrane of host cell

Virus structure

Obligate intracellular parasites Replicate only in host cells

Identification of a host cell Lock and key Viral surface proteins and specific receptor molecules of the host

Bacteriophage Virus that infects bacteria Bacterial Defenses Natural selection Restriction enzymes Lysogeny Co-exist

Lytic vs Lysogenic

Retrovirus Equipped with RNA transcriptase RNA DNA DNA can enter the nucleus into the host genome HIV

Viral Infections in Animals Damage or kill cells Produce toxins Defense tools Vaccines Anti-viral drugs

Viral infections in Plants Horizontal transmission entering through damaged cell walls Vertical transmission inheriting the virus from a parent

Viroids and Prions Viroids Prions circular RNA molecules that infect plants and disrupt their growth Prions slow-acting virtually indestructible infectious proteins brain diseases in mammals – mad cow propagate by converting normal proteins into the prion version