viruses. evolution of virus alive or not – biologically inert – unable to replicate genes –...
TRANSCRIPT
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 – 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