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Viruses- Are they alive? • • • • Acellular Can not metabolize Can’t grow or respond to environment Can’t reproduce without host • Discovery- Wendell Stanley- tobacco mosaic virus Virion- virus outside of cell • Capsid-protein coat surrounding nucleic acid • Genetic material- DNA or RNA – – – – dsDNA- double stranded DNA ssDNA- single stranded DNA dsRNA- double stranded RNA ssRNA- single stranded RNA • Super small amount of genes • Capsomeres- Surface proteins- only attach to particular host or even specific cells in the host Enveloped virion • Membrane acquired from its host cell during viral replication or release • Composed of phospholipid bilayer & proteins- specific for host attachment Bacteriophage • Infects bacteria • Replication– 2 cycles Lytic Cycle-pg 390 (virulent-causes disease) 1. Attachment - the virus attaches itself to the host cell. 2. Injection - the virus inserts its genetic material into the host cell. 3. Integration & Replication- the genetic material tells the cell what to do & the host cell builds parts of the virus. 4. Assembly - the cell assembles the replicated parts into new viruses. 5. Lysis - the cell breaks open and each replicated virus can now infect other cells. Lysogenic Cycle- pg 392 (temperate- doesn’t kill right away) 1. Attachment 2. Injection 3. Integration- virus DNA becomes part of bacterial DNA- prophage 4. Replication- when host cell replicates its own DNA, virus DNA is also copied 5. Assembly 6. Trigger > Lytic Cycle • can be caused by sunlight, radiation, chemicals Virus Life Cycle • http://www.hhmi.org/biointeractive/hiv-lifecycle?utm_source=BioInteractive+News& utm_campaign=8559c11a70BioInteractive_News_Vol_309_15_2014&u tm_medium=email&utm_term=0_98b2f5c6 ba-8559c11a70-69298381 Animations • www.youtube.com/watch?v=wVkCyU5aee U • http://www.youtube.com/watch?v=_J9xKitsd0&feature=related Viroids • Small, circular pieces of RNA that are infectious to plants • Lack capsids • May appear linear Prions • Not viruses because they lack nucleic acid • Composed of single protein- PrP – All mammals contain a gene that codes for the a.a. sequence for cellular PrP • Can re-fold into stable structures, changing shape & become harmful • Excess PrP or mutations cause the prion PrP • 40% of humans have PrP that can misfold