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Figure 10.22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings VIRUSES: GENES IN PACKAGES Viruses 1. Components 2. Infection cycle 3. DNA, RNA viruses Prions Components of a virus • envelope Membranous envelope • capsid • genetic material RNA – Ex. flu viruses Protein coat Glycoprotein spike Figure 10.18A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Phage reproductive cycle Phage attaches to bacterial cell. Phage injects DNA. Phage DNA directs host cell to make more phage DNA and protein parts. New phages assemble. Cell lyses and releases new phages. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Viral DNA may become part of the host chromosome Phage Attaches to cell Bacterial chromosome Phage DNA Cell lyses, releasing phages Phage injects DNA Many cell divisions Occasionally a prophage may leave the bacterial chromosome LYTIC CYCLE Phages assemble Phage DNA circularizes LYSOGENIC CYCLE Prophage Lysogenic bacterium reproduces normally, replicating the prophage at each cell division OR New phage DNA and proteins are synthesized Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phage DNA inserts into the bacterial chromosome by recombination Glycoprotein spike VIRUS • Viruses redirect the host cell machinery to make more viruses • Some animal viruses steal a bit of the host cell’s membrane Protein coat Viral RNA (genome) Plasma membrane of host cell Envelope 1 Entry 2 Uncoating 3 RNA synthesis by viral enzyme Viral RNA (genome) 4 Protein synthesis 5 RNA synthesis (other strand) Template mRNA New viral proteins protein 6 New viral genome Assembly Exit 7 Figure 10.18B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Plant viruses are serious agricultural pests • Most plant viruses have RNA – Example: tobacco mosaic disease Protein Figure 10.19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA • The deadly Ebola virus causes hemorrhagic fever – Each virus is an enveloped thread of protein-coated RNA • Hantavirus is another enveloped RNA virus Figure 10.20A, B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – HIV, seen here attacking a white blood cell Figure 10.22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • HIV is a retrovirus Invasion of T cell by HIV • HIV infection Figure 10.22x1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • AIDS quilt Figure 10.22x2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Other parasitic particles • Viroids - infectious RNA (no capsid) • Prions - infectious protein – Cellular PrP, prion PrP – Spongiform encephalopathies cause neural degeneration Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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