V IRAL R EPLICATION

V IRUS Like live organisms: need to replicate and create progeny. Unlike organisms: A virus cannot survive on its own. It is only active when replicating within a host, using a hosts' resources. Once inside a host, a virus's sole purpose is to make as many copies of itself, and infect other host cells.

V IRUS Infecting virus can be thought of as a set of instructions. Viral genome tricks host cell into making viruses. Viruses can only reproduce inside cells Outside, they are metabolically inert virions Virion is an inactive virus particle outside of a cell Not alive or dead but inactive or active 3

V IRUS Viruses lack their own ribosomes and enzymes for protein and nucleic acid synthesis Virus hijacks the cell’s transcription and translation machineries to express Early genes Middle genes Late genes End result is assembly and release of virusesviruses 4

PRINCIPAL EVENTS INVOLVED IN REPLICATION/L YTIC C YCLE Adsorption The first step in infection of a cell is attachment to the cell surface Penetration The virus enters the cell in a variety of ways according to the nature of the virus.

Uncoating Nucleic acid has to be sufficiently uncoated that virus replication can begin at this stage. Synthesis of viral nucleic acid and protein Many strategies are used.

Assembly/maturatio n New virus particles are assembled. There may be a maturation step that follows the initial assembly process. Release Virus may be released due to cell lysis, or, if enveloped, may bud from the cell.

THINGS TO REMEMBER Viruses have highly efficient replicative capabilities that allow for rapid evolution and acquisition of new phenotypes. Viruses replicate via a component assembly model allowing one virus to produce many progeny simultaneously via the lytic cycle. Virus replication allows for mutations to occur through usual host pathways. BozamanBozaman!

RNA VIRUSES Include the human AIDS virus, HIV During the infection process, the viral RNA enters a cell and is converted to a doublestranded DNA The term retrouirus: RNA-DNA

R ETROTRANSCRIPTION