Viruses, Viroids, and Prions 13 Viruses, Viroids, and Prions

Attachment, Penetration, and Uncoating Pinocytosis Figure 13.14a

Attachment, Penetration, and Uncoating Fusion Figure 13.14b

Release of an Enveloped Virus by Budding Figure 13.20

Multiplication of DNA Virus Figure 13.15

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

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

Multiplication of a Retrovirus PLAY Animation: Viral Replication Figure 13.19

Cancer Activated oncogenes transform normal cells into cancerous cells. Transformed cells have: increased growth loss of contact inhibition tumor specific transplant antigens

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

Table 13.5

Prions Infectious proteins Inherited and transmissible by ingestion, transplant, and surgical instruments Spongiform encephalopathies: Sheep scrapie Creutzfeldt-Jakob disease Mad cow disease PrPC: Normal cellular prion protein, on cell surface PrPSc: Scrapie protein; accumulates in brain cells forming plaques PLAY Animation: Prion Reproduction

Prions Figure 13.22

Plant viruses: Enter through wounds or via insects. Viroids: Infectious RNA; e.g., potato spindle tuber disease. Figure 13.23

Some Plant Viruses Table 13.6

Crossing the Species Barrier UN 13.3