Fig. 19-1 Figure 19.1 Are the tiny viruses infecting this E. coli cell alive? 0.5 µm

RESULTS Extracted sap from tobacco plant with tobacco mosaic disease Fig. 19-2 RESULTS 1 Extracted sap from tobacco plant with tobacco mosaic disease 2 Passed sap through a porcelain filter known to trap bacteria 3 Rubbed filtered sap on healthy tobacco plants Figure 19.2 What causes tobacco mosaic disease? 4 Healthy plants became infected

RNA DNA Membranous envelope Head RNA Capsomere DNA Capsid Tail sheath Fig. 19-3 RNA DNA Membranous envelope Head RNA Capsomere DNA Capsid Tail sheath Capsomere of capsid Tail fiber Glycoprotein Glycoproteins 18  250 nm 70–90 nm (diameter) 80–200 nm (diameter) 80  225 nm Figure 19.3 Viral structure 20 nm 50 nm 50 nm 50 nm (a) Tobacco mosaic virus (b) Adenoviruses (c) Influenza viruses (d) Bacteriophage T4

18  250 nm RNA Capsomere of capsid (a) Tobacco mosaic virus 20 nm Fig. 19-3a RNA Capsomere of capsid 18  250 nm Figure 19.3 Viral structure 20 nm (a) Tobacco mosaic virus

DNA Capsomere Glycoprotein 70–90 nm (diameter) (b) Adenoviruses 50 nm Fig. 19-3b DNA Capsomere Glycoprotein 70–90 nm (diameter) Figure 19.3 Viral structure 50 nm (b) Adenoviruses

Membranous envelope RNA Capsid Glycoproteins 80–200 nm (diameter) Fig. 19-3c Membranous envelope RNA Capsid Glycoproteins 80–200 nm (diameter) Figure 19.3 Viral structure 50 nm (c) Influenza viruses

Head DNA Tail sheath Tail fiber 80  225 nm (d) Bacteriophage T4 50 nm Fig. 19-3d Head DNA Tail sheath Tail fiber 80  225 nm Figure 19.3 Viral structure 50 nm (d) Bacteriophage T4

VIRUS Entry and uncoating DNA Capsid Transcription and manufacture Fig. 19-4 VIRUS Entry and uncoating 1 DNA Capsid Transcription and manufacture of capsid proteins 3 2 Replication HOST CELL Viral DNA mRNA Viral DNA Capsid proteins Figure 19.4 A simplified viral reproductive cycle Self-assembly of new virus particles and their exit from the cell 4

Fig. 19-5-1 1 Attachment Figure 19.5 The lytic cycle of phage T4, a virulent phage

Attachment Entry of phage DNA and degradation of host DNA 1 2 Fig. 19-5-2 1 Attachment 2 Entry of phage DNA and degradation of host DNA Figure 19.5 The lytic cycle of phage T4, a virulent phage

Attachment 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 Figure 19.5 The lytic cycle of phage T4, a virulent phage 3 Synthesis of viral genomes and proteins

Attachment Entry of phage DNA and degradation of host DNA Fig. 19-5-4 1 Attachment 2 Entry of phage DNA and degradation of host DNA Phage assembly Figure 19.5 The lytic cycle of phage T4, a virulent phage 4 Assembly 3 Synthesis of viral genomes and proteins Head Tail Tail fibers

Attachment Entry of phage DNA and degradation of host DNA Release Fig. 19-5-5 1 Attachment 2 Entry of phage DNA and degradation of host DNA 5 Release Phage assembly Figure 19.5 The lytic cycle of phage T4, a virulent phage 4 Assembly 3 Synthesis of viral genomes and proteins Head Tail Tail fibers

The phage injects its DNA. Fig. 19-6 Daughter cell with prophage Phage DNA 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 Lysogenic cycle is entered Figure 19.6 The lytic and lysogenic cycles of phage λ, a temperate phage Prophage New phage DNA and proteins are synthesized and assembled into phages. Phage DNA integrates into the bacterial chromosome, becoming a prophage.

Table 19-1 Table 1

Table 19-1a Table 1

Table 19-1b Table 1

Capsid and viral genome enter the cell Capsid 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 Copy of genome (RNA) Glyco- proteins Figure 19.7 The reproductive cycle of an enveloped RNA virus New virus

Fig. 19-8 Glycoprotein Viral envelope Capsid RNA (two identical strands) Reverse transcriptase HIV Membrane of white blood cell HIV HOST CELL Reverse transcriptase Viral RNA RNA-DNA hybrid 0.25 µm HIV entering a cell DNA NUCLEUS Provirus Chromosomal DNA Figure 19.8 The reproductive cycle of HIV, the retrovirus that causes AIDS RNA genome for the next viral generation mRNA New virus New HIV leaving a cell

Viral envelope Glycoprotein Capsid RNA (two identical strands) Reverse Fig. 19-8a Glycoprotein Viral envelope Capsid RNA (two identical strands) Reverse transcriptase HOST CELL HIV Reverse transcriptase Viral RNA RNA-DNA hybrid DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation Figure 19.8 The reproductive cycle of HIV, the retrovirus that causes AIDS mRNA New virus

Membrane of white blood cell HIV HIV entering a cell Fig. 19-8b Membrane of white blood cell HIV Figure 19.8 The reproductive cycle of HIV, the retrovirus that causes AIDS 0.25 µm HIV entering a cell New HIV leaving a cell

(a) The 1918 flu pandemic (b) Influenza A H5N1 virus Fig. 19-9 (a) The 1918 flu pandemic 0.5 µm Figure 19.9 Influenza in humans and other animals For the Discovery Video Emerging Diseases, go to Animation and Video Files. (b) Influenza A H5N1 virus (c) Vaccinating ducks

(a) The 1918 flu pandemic Fig. 19-9a Figure 19.9 Influenza in humans and other animals (a) The 1918 flu pandemic

(b) Influenza A H5N1 virus 0.5 µm Fig. 19-9b Figure 19.9 Influenza in humans and other animals (b) Influenza A H5N1 virus

(c) Vaccinating ducks Fig. 19-9c Figure 19.9 Influenza in humans and other animals (c) Vaccinating ducks

Fig. 19-10 Figure 19.10 Viral infection of plants

Fig. 19-10a Figure 19.10 Viral infection of plants

Fig. 19-10b Figure 19.10 Viral infection of plants

Fig. 19-10c Figure 19.10 Viral infection of plants

Original Prion prion Aggregates of prions New prion Normal protein Fig. 19-11 Original prion Prion Aggregates of prions New prion Normal protein Figure 19.11 Model for how prions propagate

host cell and injects its DNA Phage DNA Fig. 19-UN1 The phage attaches to a host cell and injects its DNA Phage DNA Bacterial chromosome Prophage Lytic cycle Lysogenic cycle Virulent or temperate phage Destruction of host DNA Production of new phages Lysis of host cell causes release of progeny phages 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

Fig. 19-UN2 A B Number of bacteria Number of viruses Time Time

Fig. 19-UN3

You should now be able to: Explain how capsids and envelopes are formed Distinguish between the lytic and lysogenic reproductive cycles Explain why viruses are obligate intracellular parasites Describe the reproductive cycle of an HIV retrovirus Describe three processes that lead to the emergence of new diseases Describe viroids and prions