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Viruses: Acellular Organisms with Unique Replication Mechanisms

Explore the fascinating world of viruses, their characteristics, and their replication mechanisms. Discover the difference between lytic and lysogenic cycles, learn how animal viruses replicate, and explore other viral agents such as viroids and prions. Understand the importance of vaccines in preventing viral infections.

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Viruses: Acellular Organisms with Unique Replication Mechanisms

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  1. 19-3 VirusesAre they alive? Yes No • Acellular • Can not metabolize • Can’t grow or respond to environment • Can’t reproduce without host- obligate parasites • Have DNA or RNA • Evolve • *can only be seen with electron microscope

  2. 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

  3. 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

  4. Bacteriophage • Infects bacteria • Replication- • 2 cycles

  5. Enveloped virion • Membrane acquired from its host cell during viral replication or release • Composed of phospholipid bilayer & proteins- specific for host attachment

  6. Lytic Cycle(virulent-causes disease) • Attachment - the virus attaches itself to the host cell. • Injection - the virus inserts its genetic material into the host cell. • Integration &Replication- the genetic material tells the cell what to do & the host cell builds parts of the virus. • Assembly - the cell assembles the replicated parts into new viruses. • Lysis - the cell breaks open and each replicated virus can now infect other cells.

  7. Lysogenic Cycle(temperate- doesn’t kill right away) • Attachment • Injection • Integration- virus DNA becomes part of bacterial DNA- prophage • Replication- when host cell replicates its own DNA, virus DNA is also copied • Assembly • Trigger > Lytic Cycle • can be caused by sunlight, radiation, chemicals

  8. Lytic vs Lysogenic Cycles • www.youtube.com/watch?v=wVkCyU5aeeU • http://www.youtube.com/watch?v=_J9-xKitsd0&feature=related

  9. How do Animal viruses replicate? • Same steps as bacteriophages, just some differences in what is happening in each • Ex: removal of outer coat

  10. 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

  11. Viroids • Small, circular pieces of RNA that are infectious to plants • Lack capsids • May appear linear

  12. 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

  13. Retroviruses • Work “backwards” • RNA > DNA > RNA > Protein • HIV • http://www.youtube.com/watch?v=eS1GODinO8w

  14. Treeman • http://www.hlntv.com/video/2013/10/03/tree-man-genetic-condition-growths-hands-legs

  15. Vaccines • How are they made? • Reading • http://content.time.com/time/video/player/0,32068,60312463001_1951560,00.html

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