Download Viruses: viruses are not considered to be living organisms do not

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