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Review: characteristics of living things cladistics phylogeny dichotomous keys Dec 23:01 PM Viruses: viruses are not considered to be living organisms do not have cellular structure and are not included in the six kingdoms viruses invade the cells of organisms and use the metabolism of a host cell to reproduce a virus consists of strands of DNA or RNA surrounded by a protective protein coat called a capsid Dec 23:03 PM 1 viruses can come in various shapes Dec 23:07 PM Where do viruses come from? a virus cannot reproduce without a host viruses probably started as fragments of nucleic acids that escaped from their original cells nucleic acids are complex compounds carrying hereditary information this would suggest that viruses and their hosts (cells) are closely related and why viruses are able to infect certain cells but not others Dec 23:09 PM 2 Viral Replication of a T4 Virus (a) Attachment: T4 virus attaches to a specific receptor site on a hosts cell wall (ecoli bacteria) weak bonds form joining the virus to the host (b) Entry: T4 injects its nucleic acid (DNA) into the bacteria host the viral DNA passes into the cell while the capisid remains outside Dec 23:12 PM (c) Replication hosts protein synthesis is stopped by viral degradation of the host DNA the hosts metabolism instead starts to replicate the viral DNA (d) Assembly spontaneous assembly of new viruses occur in the host cell Dec 23:16 PM 3 (e) Lysis and release the host cell membrane and cell wall break open (lyses) this releases the new virus particles and the cell dies *see diagrams on pages 122 and 123 Dec 23:17 PM Dec 23:21 PM 4 Readings: Pages 122 126 Questions: Page 126: #'s 1,2,5,6,10 Dec 23:22 PM 5