Download 19-3 Viruses

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.
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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.
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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