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No 19-3 Viruses Are they alive? Yes • Acellular • Have DNA or RNA • Can not metabolize • Evolve • Can’t grow or respond to environment • Can’t reproduce without host- obligate parasites • *can only be seen with electron microscope 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 Discovery- they were looking for the cause of Tobacco Mosaic Virus • 1883- Adolf Mayer-disease is contagious • 1892- Dmitri Ivanovsky- uses filter to trap “bacteria” • 1897-Martinus Beijerinch- caused by something smaller than bacteria • 1898-named virus- meaning “poison” • 1935- Wendell Stanley- isolates virus Bacteriophage • Infects bacteria • Replication– 2 cycles Enveloped virion • Membrane acquired from its host cell during viral replication or release • Composed of phospholipid bilayer & proteins- specific for host attachment Lytic Cycle (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 (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 Lytic vs Lysogenic Cycles • www.youtube.com/watch?v=wVkCyU5aee U • http://www.youtube.com/watch?v=_J9xKitsd0&feature=related How do Animal viruses replicate? • Same steps as bacteriophages, just some differences in what is happening in each – Ex: removal of outer coat Latency • -viruses remain dormant in cells • Prolonged viral activity for years – Ex: chickenpox, herpes • Can become integrated into host’s chromosomal information permanently, so all cells after that are infected – Ex: HIV 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 Retroviruses • Work “backwards” – RNA > DNA > RNA > Protein – HIV – http://www.youtube.com/watch?v=eS1GODin O8w Treeman • http://www.hlntv.com/video/2013/10/03/tre e-man-genetic-condition-growths-handslegs Vaccines • How are they made? – Reading – http://content.time.com/time/video/player/0,32 068,60312463001_1951560,00.html