1.  Chapter 18~ Microbial Models: The Genetics of Viruses and Bacteria

2. Fig. 19-1 0.5 µm

3. Viral structure  Virus: “poison” (Latin)- infectious particles consisting of a nucleic acid in a protein coat  Viral Genomes (Can be) –double stranded DNA –single stranded DNA –double stranded RNA –single stranded RNA

4. Table 19-1

5. Table 19-1a

6. Table 19-1b

7. Viral structure  Capsids and Envelopes –Capsid- Protein shell that encloses the viral genome  Can be difference shapes depending on type of virus ( rod shaped, helical, polyhedral)  Built from Capsomeres which are protein subunits  Most complex in bacteriophages  Viral Envelopes –Almost like cloak that surrounds capsids –Many animal viruses have these –Derived from host cell membrane but also contain glycoproteins of viral origin

9. Viral reproduction: Lytic Cycle  Host range: infection of a limited range of host cells (receptor molecules on the surface of cells) –Most viruses are tissue specific  The lytic cycle: Results in death of host cell –1- attachment –2- injection –3- hydrolyzation –4- assembly –5- release  Virulent virus (phage reproduction only by the lytic cycle)

11. Viral reproduction: Lysogenic Cycle  Genome replicated w/o destroying the host cell  Genetic material of virus becomes incorporated into the host cell DNA (prophage DNA)  Temperate virus (phages capable of using the lytic and lysogenic cycles)  May give rise to lytic cycle

13. Animal Viruses  Most are RNA viruses –Some RNA viruses use their RNA to serve directly as mRNA which can be immediately transcribed –Others must use their RNA as a templates to make mRNA –And yet others, like retroviruses enzymes like reverse transcriptase in their reproduction cycle

14. Fig. 19-7 Capsid RNA Envelope (with glycoproteins) Capsid and viral genome enter the cell HOST CELL Viral genome (RNA) Template mRNA ER Glyco- proteins Capsid proteins Copy of genome (RNA) New virus

15. RNA viruses  Retroviruses: transcribe DNA from an RNA template (RNA to DNA and DNA to mRNA)  Reverse transcriptase (catalyzing enzyme)  HIV--->AIDS

16. How do we fight viral disease?  Vaccines –Edward Jenner made first vaccine using cowpox –Vaccines are made from non- virulent viruses

17. Viroids and prions  Viroids: tiny, naked circular RNA that infect plants; does not code for proteins, but use cellular enzymes to reproduce; stunt plant growth  Prions: “infectious proteins”; “mad cow disease”; trigger chain reaction conversions; a transmissible protein

18. Emerging Viruses  Emerging viruses are those that appear suddenly or suddenly come to the attention of scientists  Outbreaks of “new” viral diseases in humans are usually caused by existing viruses that expand their host territory  Viral diseases in a small isolated population can emerge and become global causing pandemics.