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Fig. 19-1 0.5 µm Fig. 19-2 RESULTS 1 Extracted sap 2 Passed sap from tobacco plant with tobacco mosaic disease 3 Rubbed filtered through a porcelain filter known to trap bacteria 4 Healthy plants became infected sap on healthy tobacco plants Fig. 19-3 RNA DNA Capsomere Membranous envelope RNA Head DNA Capsid Tail sheath Capsomere of capsid Glycoproteins Glycoprotein 18 250 nm 70–90 nm (diameter) 80–200 nm (diameter) 20 nm 50 nm (a) Tobacco mosaic (b) Adenoviruses virus 50 nm Tail fiber 80 225 nm 50 nm (c) Influenza viruses (d) Bacteriophage T4 Fig. 19-3a RNA Capsomere of capsid 18 250 nm 20 nm (a) Tobacco mosaic virus Fig. 19-3b DNA Capsomere Glycoprotein 70–90 nm (diameter) 50 nm (b) Adenoviruses Fig. 19-3c Membranous envelope RNA Capsid Glycoproteins 80–200 nm (diameter) 50 nm (c) Influenza viruses Fig. 19-3d Head DNA Tail sheath Tail fiber 80 225 nm 50 nm (d) Bacteriophage T4 Fig. 19-4 VIRUS 1 Entry and DNA uncoating Capsid 3 Transcription and manufacture of capsid proteins 2 Replication HOST CELL Viral DNA mRNA Viral DNA Capsid proteins 4 Self-assembly of new virus particles and their exit from the cell Fig. 19-5-1 1 Attachment Fig. 19-5-2 1 Attachment 2 Entry of phage DNA and degradation of host DNA Fig. 19-5-3 1 Attachment 2 Entry of phage DNA and degradation of host DNA 3 Synthesis of viral genomes and proteins Fig. 19-5-4 1 Attachment 2 Entry of phage DNA and degradation of host DNA Phage assembly 4 Assembly 3 Synthesis of viral genomes and proteins Head Tail Tail fibers Fig. 19-5-5 1 Attachment 2 Entry of phage 5 Release DNA and degradation of host DNA Phage assembly 4 Assembly 3 Synthesis of viral genomes and proteins Head Tail Tail fibers Fig. 19-6 Phage DNA Daughter cell with prophage The phage injects its DNA. Cell divisions produce population of bacteria infected with the prophage. Phage DNA circularizes. Phage Bacterial chromosome Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Lytic cycle Lysogenic cycle The bacterium reproduces, copying the prophage and transmitting it to daughter cells. The cell lyses, releasing phages. Lytic cycle is induced or New phage DNA and proteins are synthesized and assembled into phages. Lysogenic cycle is entered Prophage Phage DNA integrates into the bacterial chromosome, becoming a prophage. Table 19-1 Table 19-1a Table 19-1b Fig. 19-7 Capsid and viral genome enter the cell Capsid RNA HOST CELL Envelope (with glycoproteins) Viral genome (RNA) Template mRNA Capsid proteins ER Glycoproteins Copy of genome (RNA) New virus Fig. 19-8 Glycoprotein Viral envelope Capsid Reverse transcriptase HIV RNA (two identical strands) HIV Membrane of white blood cell HOST CELL Reverse transcriptase Viral RNA RNA-DNA hybrid 0.25 µm DNA HIV entering a cell NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation New virus New HIV leaving a cell mRNA Fig. 19-8a Glycoprotein Viral envelope Capsid Reverse transcriptase RNA (two identical strands) HOST CELL HIV Reverse transcriptase Viral RNA RNA-DNA hybrid DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation New virus mRNA Fig. 19-8b HIV Membrane of white blood cell 0.25 µm HIV entering a cell New HIV leaving a cell Fig. 19-9 (a) The 1918 flu pandemic 0.5 µm (b) Influenza A H5N1 virus (c) Vaccinating ducks Fig. 19-9a (a) The 1918 flu pandemic Fig. 19-9b 0.5 µm (b) Influenza A H5N1 virus Fig. 19-9c (c) Vaccinating ducks Fig. 19-10 Fig. 19-10a Fig. 19-10b Fig. 19-10c Fig. 19-11 Prion Normal protein Original prion New prion Aggregates of prions Fig. 19-UN1 Phage DNA The phage attaches to a host cell and injects its DNA Bacterial chromosome Lytic cycle • Virulent or temperate phage • Destruction of host DNA • Production of new phages • Lysis of host cell causes release of progeny phages Prophage Lysogenic cycle • Temperate phage only • Genome integrates into bacterial chromosome as prophage, which (1) is replicated and passed on to daughter cells and (2) can be induced to leave the chromosome and initiate a lytic cycle Number of bacteria A Time Number of viruses Fig. 19-UN2 B Time Fig. 19-UN3