1. CH.19 Viruses

2. OVERVIEW P.381 Latin: virus means poison Def.: A virus is an infectious particle consisting of little more than genes packaged in a protein coat. Viruses are much smaller than Bacteria which are much smaller than Eukaryotic cells. Bacteriophage “Bacteria Eater”

3. OVERVIEW P.381 ARE VIRUSES LIVING OR NONLIVING? Living DNA/RNA Reproduce Evolve Metabolism Communication Homeostasis Nonliving No Cell Structures Can’t reproduce or carry out metabolism w/o host cell “Borrowed Life” “Gene transfer vehicles”

4. 19.1 VIRUS = N.A. + PROTEIN History 1883 Adolf Mayer-Tobacco mosaic disease. Ivanowsky-Bacterial filter Beijerinck-named virus 1935 Wendell Stanley- crystallization process. Structure 20nm dia.-smaller than a ribosome. Millions can fit on one pinhead. Double or single-stranded DNA or RNA. 200-2000 gene.

5. 19.1 VIRUS = N.A. + PROTEIN Capsid Protein shell enclosing viral genome. Three basic shapes:  Bacillus-Rod  Cocci-Spherical  Spirillum-Spiral

6. 19.1 VIRUS = N.A. + PROTEIN Viral Envelopes Accessory structures that help viruses infect hosts. Derived from membranes of host’s cell. Most complex capsids are bacteriophages.

7. 19.2 VIRUSES REPLICATE ONLY IN HOST CELLS Host range-host species a virus can infect via surface glycoprotein receptors. Some viruses have broad host range. Ex. West Nile Some viruses have very narrow host range. Ex. Measles Many viruses can only infect certain types of tissue. Ex. Cold, HIV

8. 19.2 VIRUSES REPLICATE ONLY IN HOST CELLS Viral Replicative Cycles 1. Binds to and enters host cell.  Some may lie dormant for years. 2. Commandeers and reprograms host. 3. Host begins making viruses. 4. Host cell releases viruses to attack new cells.

9. 19.2 VIRUSES REPLICATE ONLY IN HOST CELLS Phage Replication 1. Attachment 2. Injection 3. Synthesis 4. Assembly 5. Lysis-virulent phage *Many Bacteria produce restriction enzymes which cut up and destroy viral DNA/RNA.

10. 19.2 VIRUSES REPLICATE ONLY IN HOST CELLS Lysogenic Cycle Host is not destroyed, virus DNA becomes part of genome and Lytic cycle can be turned on.

11. 19.2 VIRUSES REPLICATE ONLY IN HOST CELLS Classes of Animal Viruses Table 19.1 p.387 I. Double-Stranded DNA (dsDNA) II. Single-Stranded DNA (ssDNA) III. Double-Stranded RNA (dsRNA) IV. Single-Stranded RNA (ssRNA); serves as mRNA V. ssRNA; Template for mRNA Synthesis VI. ssRNA; Template for DNA Synthesis

12. 19.2 VIRUSES REPLICATE ONLY IN HOST CELLS Retroviruses have the most complex replication cycle (class VI). Ex. HIV Fig. 19.8 p.389 1. Envelopes bind. 2. Virus fuses. 3. Reverse transcriptionase makes DNA. 4. Reverse transcriptionase make complimentary DNA.

13. 19.2 VIRUSES REPLICATE ONLY IN HOST CELLS 5. DNA incorporated in host’s DNA (provirus). 6. Genes transcribed. 7. Synthesis of capsid proteins. 8. Vesicles transport glycoproteins to cell’s membrane. 9. Capsids are assembled around viral genomes & reverse transcriptase. 10. New viruses bud off from the host cell.

14. 19.2 VIRUSES REPLICATE ONLY IN HOST CELLS Evolution of Viruses Infect every form of life. Probably appeared after cells. Original source probably plasmids or transposons. Mimivirus debate.

15. 19.3 VIRAL PATHOGENS Vaccines-immunity Antiviral drugs-slow/stop replication. Ex. AZT Emerging Viruses-epidemics: HIV, Ebola, West Nile, H1N1 (2009). Spanish Flu Pandemic (1918) 500 million infected, 50-100 million deaths.

16. 19.3 VIRAL PATHOGENS High mutation rates. Method of transfer. Animals to Humans. Ex. Swine Flu, Bird Flu.

17. 19.3 VIRAL PATHOGENS Viral Diseases in Plants 2,000 known types. $15 billion crop damage/year. Horizontal & Vertical transmission.

18. 19.3 VIRAL PATHOGENS Viroids Circular RNA molecules, only a few hundred nucleotides long, that infect plants. Abnormal development and stunted growth. Prions Infectious proteins. Cause degenerative brain disease. Ex. Mad Cow disease, Kuru. Transmitted in food. Incubation period of at least ten years. Virtually indestructible. 1997 Nobel Prize-Prusiner.