Growing Viruses

1. Growing Viruses • Animal viruses may be grown in living animals or in embryonated eggs. Figure 13.7

2. Growing Viruses • Animal and plants viruses may be grown in cell culture. • Continuous cell lines may be maintained indefinitely. Figure 13.8

3. Virus Identification • Cytopathic effects • Serological tests • Detect antibodies against viruses in a patient. • Use antibodies to identify viruses in neutralization tests, viral hemagglutination, and Western blot. • Nucleic acids • RFLPs • PCR

4. Virus Identification Figure 13.9

5. Multiplication of Bacteriophages (Lytic Cycle) • Attachment: Phage attaches by tail fibers to host cell. • Penetration: Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell. • Biosynthesis: Production of phage DNA and proteins. • Maturation: Assembly of phage particles. • Release: Phage lysozyme breaks cell wall.

6. 1 2 3 Figure 13.11, steps 1–3, 6–7

7. 4 Figure 13.11, steps 4–5, 8

8. One-Step Growth Curve Figure 13.10

9. Lytic cycle: Phage causes lysis and death of host cell. • Lysogenic cycle: Prophage DNA incorporated in host DNA.

10. The Lysogenic Cycle Figure 13.12

11. Specialized Transduction 2 3 4 5 6 Figure 13.13

12. Multiplication of Animal viruses • Attachment: Viruses attach to cell membrane. • Penetration by endocytosis or fusion. • Uncoating by viral or host enzymes. • Biosynthesis: Production of nucleic acid and proteins. • Maturation: Nucleic acid and capsid proteins assemble. • Release by budding (enveloped viruses) or rupture.

13. Attachment, Penetration, and Uncoating • Pinocytosis Figure 13.14a

14. Attachment, Penetration, and Uncoating • Fusion Figure 13.14b

15. Release of an Enveloped Virus by Budding Figure 13.20

16. Multiplication of DNA Virus Figure 13.15

17. Attachment Capsid Nucleus RNA Cytoplasm Host cell Entry and uncoating Maturation and release Translation and synthesis of viral proteins RNA replication by viral RNA- dependent RNA polymerase Uncoating releases viral RNA and proteins. – strand is transcribed from + viral genome. Capsid protein Viral protein Viral genome (RNA) (a) ssRNA; + or sense strand; Picornaviridae + strand mRNA is transcribed from the – strand. + Sense Strand (+ Strand) RNA Virus Figure 13.17a

18. Attachment Capsid Nucleus RNA Cytoplasm Host cell Entry and uncoating Maturation and release Translation and synthesis of viral proteins RNA replication by viral RNA- dependent RNA polymerase Uncoating releases viral RNA and proteins. The + strand (mRNA) must first be transcribed from the – viral genome before proteins can be synthesized. Viral protein Viral genome (RNA) Capsid protein (b) ssRNA; – or antisense strand; Rhabdoviridae – strands are incorporated into capsid Additional – strands are transcribed from mRNA. — Antisense Strand (— Strand) RNA Virus Figure 13.17b

19. Attachment Capsid Nucleus RNA Cytoplasm Host cell Entry and uncoating Maturation and release RNA replication by viral RNA- dependent RNA polymerase Translation and synthesis of viral proteins Uncoating releases viral RNA and proteins. mRNA is produced inside the capsid and released into the cytoplasm of the host. RNA polymerase initiates production of – strands. The mRNA and – strands form the dsRNA that is incorporated as new viral genome. Viral protein Viral genome (RNA) (c) dsRNA; + or sense strand with – or antisense strand; Reoviridae Capsid proteins and RNA- dependent RNA polymerase Double-Stranded RNA Virus Figure 13.17c

20. Pathways of Multiplication for RNA-Containing Viruses Figure 13.17

21. Multiplication of a Retrovirus Figure 13.19

22. DNA and RNA Viruses Compared • DNA: Cellular enzyme transcribes viral DNA in nucleus. • DNA, reverse transcriptase: Cellular enzyme transcribes viral DNA in nucleus; reverse transcriptase copies mRNA to make viral DNA. • RNA, + strand: Viral RNA is a template for synthesis of RNA polymerase.

23. DNA and RNA Viruses Compared • RNA – strand: Viral enzyme copies viral RNA to make mRNA in cytoplasm. • RNA, double-stranded: Viral enzyme copies – strand RNA to make mRNA in cytoplasm. • RNA, reverse transcriptase: Viral enzyme copes viral RNA to make DNA in cytoplasm.

24. Cancer • Activated oncogenes transform normal cells into cancerous cells. • Transformed cells have increased growth, loss of contact inhibition, tumor specific transplant and T antigens. • The genetic material of oncogenic viruses becomes integrated into the host cell's DNA.

25. Oncogenic DNA viruses Adenoviridae Heresviridae Poxviridae Papovaviridae Hepadnaviridae Oncogenic RNA viruses Retroviridae Viral RNA is transcribed to DNA which can integrate into host DNA HTLV 1 HTLV 2 Oncogenic Viruses

26. Latent viral infections • Virus remains in asymptomatic host cell for long periods. • Cold sores, shingles • Presistent viral infections • Disease processes occurs over a long period; generally is fatal. • Subacute sclerosing panencephalitis (measles virus) Figure 13.21