13 Viruses, Viroids, and Prions
Viruses • Contain DNA or RNA • Contain a protein coat • Some are enclosed by an envelope • Most viruses infect only specific types of cells in one host
Viruses Figure 13.1
Helical Viruses Figure 13.4a–b
Polyhedral Viruses Figure 13.2a–b
Enveloped Viruses Figure 13.3
Complex Viruses Figure 13.5a
Viral Taxonomy • Family names end in -viridae. • Genusnames end in -virus. • Viral species: A group of viruses sharing the same genetic information and ecological niche (host). Common names are used for species. • Subspecies are designated by a number.
Herpesviridae Simplexvirus Human herpes virus HHV-1, HHV-2, HHV-3 Retroviridae Lentivirus Human immunodeficiency virus HIV-1, HIV-2 Viral Taxonomy
Growing Viruses • Viruses must be grown in living cells. • Bacteriophages form plaques on a lawn of bacteria. Figure 13.6
Growing Viruses • Animal viruses may be grown in living animals or in embryonated eggs. Figure 13.7
Growing Viruses • Animal and plants viruses may be grown in cell culture. • Continuous cell lines may be maintained indefinitely. Figure 13.8
Virus Identification The cytopathic effect of viruses Figure 13.9
Virus Identification • Cytopathic effects • Serological tests • Detect antibodies against viruses in a patient. • Nucleic acids • PCR
Multiplication of Bacteriophages (Lytic Cycle) • Attachment • Penetration • Biosynthesis • Maturation • Release
1 2 3 Figure 13.11, steps 1–3, 6–7
4 Figure 13.11, steps 4–5, 8
One-Step Growth Curve Figure 13.10
Two Possible Life Cycles • Lytic cycle: Phage causes lysis and death of host cell. • Lysogenic cycle: Prophage DNA incorporated in host DNA.
The Lysogenic Cycle Figure 13.12
Bacterial Toxins Resulting from Phage Genes • Scarlet Fever – Streptococci • Botulism – Clostridium Botulinum • Cholera – Vibrio cholerae
Specialized Transduction 2 3 4 5 6 Figure 13.13
Multiplication of Animal viruses • Attachment • Penetration • Uncoating • Biosynthesis • Maturation • Release by budding (enveloped viruses) or rupture.