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Chapter 19: Viruses and Bacteria (19-3) Virus means “poison” Vary in shape and structure A typical virus is composed of a core of either DNA or RNA surrounded by a protein coat (capsid). Viruses “sneak” inside cells… and have the cell copy its DNA. Viruses are species specific Bacteriophages attack bacteria In a lytic infection, a virus enters a cell, makes a copy of itself, and causes the cell to burst. The host cell cannot recognize the viral DNA. The cell makes viral mRNA…this mRNA takes over the cell… and synthesizes 1000s of copies. The infected cell lyses—“bursts” Chapter 19: Viruses and Bacteria (19-3) In a lysogenic infection, a virus embeds its DNA into the cell and is replicated along with the host cell’s DNA. Do NOT lyse the host cell away. Viral DNA becomes part of the hosts DNA…(prophage.) The prophage will remain this way for a varied amount of time. Some “factors” will activate the prophage, and the cell will start making viruses. Smallpox, polio, measles, AIDS, mumps, flu, rabies, hepatitis, cold, etc. Vaccines are the best protection against viruses. Vaccines (dead, weakened, or parts of a virus), give the immune system a head start. Oncogenic virus—causes cancer because they disturb the cells replication process. Viruses that contain RNA are Retroviruses…HIV RNA to DNA…backwards process