My_Ch18_lecture(2009030423522681)

My_Ch18_lecture(2009030423522681) - Chapter 18 Molecular...

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Unformatted text preview: Chapter 18: Molecular Genetics of Viruses & Bacteria Purpose —to understand the differences in the molecular genetics of viruses and bacteria What you MUST know from Ch 18 : Viral structure Lytic cycle vs. Lysogenic cycle Reverse transcriptase Viroid vs. prion Transformation vs. conjugation Transposition (transposons) Operons (lac vs tryp) Note: for this unit, the “must know” topics are primarily in Ch 17, 18, and 20. Cliff’s has a good, concise review of Ch 18 topics for the AP exam. Viruses and bacteria are pathogens , which cause disease in the organisms that they enter. They are different, so the infectious diseases that they cause are treated differently. Structure of viruses A virus is a genome, either DNA or RNA, enclosed in a protein coat. (fig 18.2, p 321) • The protein coat is called a capsid • Some capsids contain a viral envelope , which is a membrane derived from the phospholipids and proteins from the host cell’s plasma membrane. o The viral envelope helps the virus to enter the host cell Viruses are parasites of cells ; they must enter a host cell to replicate. The host cell may be destroyed or killed in the process of viral take-over and replication, depending on the type of viral replication. Viruses are specific for the cells that they parasitize . • Bacteriophages (= phages ) are viruses that attack and replicate only in bacteria Viral reproduction for DNA viruses : Lytic cycle: • See fig 18.4, p 323 for a diagram of the lytic cycle • Virulent viruses reproduce only by the lytic cycle (can kill many host cells quickly) • Kills the host cell • Virus enters the host cell, injects viral DNA into cell • And then uses the enzymes of the host cell to replicate viral DNA and then transcribe and translate the viral DNA into viral proteins • The viral proteins and viral DNA are assembled into many new viruses, • Which lyse (break open) the host cell (thus, lytic cycle ), destroying the host cell • The new viruses then infect other host cells, and the process repeats, and the viral infection spreads • = short incubation period (time between exposure to virus and symptoms of illness start) Lysogenic cycle: • See fig 18.5, p 324 • Does not kill the host cell directly • Temperate viruses can use both the lytic and lysogenic cycles to replicate • Virus enters the cell, injects viral DNA into cell •...
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My_Ch18_lecture(2009030423522681) - Chapter 18 Molecular...

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