1. Microbial Models n The Genetics of Viruses and Bacteria

2. Viral structure n Virus: “poison” (Latin); infectious particles consisting of a nucleic acid in a protein coat n Capsid; (viral envelopes); DNA or RNA n Bacteriophages (phages)

3. Viral reproduction: Lytic Cycle n Host range: infection of a limited range of host cells (receptor molecules on the surface of cells) n The Lytic cycle : n 1- attachment n 2- injection n 3- hydrolyzation of Host DNA n 4- assembly n 5- release (bursts from osmotic swelling) n Results in death of host cell n Virulent virus (phage reproduction only by the lytic cycle) n May take only 30 minutes at 37 0 Bacteria have defenses: Restriction Enzymes!!

4. Viral reproduction: Lysogenic Cycle n Genome replicated w/o destroying the host cell n Genetic material of virus becomes incorporated into the host cell DNA (prophage* DNA) n * Called a “provirus” in Eukaryotes n Prophage usually codes for repressors which temporarily turn off virulent properties. n Temperate virus (phages capable of using the lytic and lysogenic cycles) n May give rise to lytic cycle

5. Lytic & Lysogenic Cycles: D:\bc_campbell_biology_7\0,7052,3117226-,00.html Other methods of infection: http://www.blackwellpublishing.com/

6. RNA viruses n Retroviruses: transcribe DNA from an RNA template (RNA makes DNA!) n RNA is double stranded but only one is a coding strand (the “+” strand) n Reverse transcriptase (catalyzing enzyme) n Viral DNA integrates itself as a “provirus” in t-lymphocyte cell. n HIV can lead to AIDS if it goes into lytic cycle or sufficiently taxes the t- lymphocytes.

7. Retrovirus (HIV) n D:\bc_campbell_biology_7\0,7052,3117226-,00.html D:\bc_campbell_biology_7\0,7052,3117226-,00.html

8. Vaccines: n Harmless variants or derivatives pathogenic microbes that mobilize the immune system. n Sometimes use “attenuated viruses”: ones that are just modified or weakened versions. n Work best for viruses that don’t mutate as quickly or easily. (Double stranded)

9. Emerging Viruses n Ones that “seem” to make a sudden appearance. n In reality, they not likely to be “new”, but have simply expanded their host territory. n Some examples: n May evolve or mutate continuously n May spread from one host species to another. n May have disseminated from a small isolated population n May be “released” by environmental disturbances (Ex.- Global Warming)

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

11. Bacterial genetics n Nucleoid: region in bacterium densely packed with DNA (no membrane) Usually circular. n Contain 1/1000 the DNA of Eukaryotes. n Plasmids: small circles of DNA separate from the main ring. n Plasmids replicate along with other DNA or sometimes just on its own. n Episome- a plasmid that can reversibly incorporate itself into the regular genome of the bacteria. n Reproduction: binary fission (asexual) n Mutations are rare (as usual) but impact bacterial variation more because of such rapid rates of reproduction.

12. Bacterial DNA-transfer processes n Transformation: genotype alteration by the uptake of naked, foreign DNA from the environment. Some can be”made competent” by successive heating & cooling or adding calcium ions.http://www.learner.org/http://www.learner.org/ n Transduction: phages that carry bacterial genes from 1 host cell to another generalized~ random transfer of host cell chromosome specialized~ incorporation of prophage DNA into host chromosome n Conjugation: direct transfer of genetic material; cytoplasmic bridges; sexual pili http://www.learner.org http://www.learner.org For 8 th edition. Section 27.2 ( pages 561-564)

13. Bacterial Plasmids n Small, circular, self-replicating DNA separate from the bacterial chromosome n F (fertility) Plasmid: codes for the production of sex pili (F+ or F-) n R (resistance) Plasmid: codes for antibiotic drug resistance n Transposons: transposable genetic element; piece of DNA that can move from location to another in a cell’s genome (chromosome to plasmid, plasmid to plasmid, etc.); also called “jumping genes” n http://highered.mcgraw-hill.com/sites/dl/free/0072556781/192785/anim0039.swf http://highered.mcgraw-hill.com/sites/dl/free/0072556781/192785/anim0039.swf

14. Transposition in Detail: n Transposase recognizes the inverted repeats Targeted inverted repeats are cut, and the target is cut, then the transposon is inserted For 8 th edition, see: section 21.3 & 21.4 (pp 432-438)

15. Operons: n Repressible (trp operon): n tryptophan (a.a.) synthesis n promoter: RNA polymerase binding site; begins transcription n operator: controls access of RNA polymerase to genes (tryptophan not present) n repressor: protein that binds to operator and prevents attachment of RNA polymerase ~ coded from a regulatory gene (tryptophan present ~ acts as a corepressor) n transcription is repressed when tryptophan binds to a regulatory protein Def: Unit of genetic function consisting of coordinately related clusters of genes with related functions (transcription unit) FOUND ONLY IN PROKARYOES!!! (NOT Eukaryotes)

16. Operons, continued n Inducible (lac operon): n lactose metabolism n lactose not present: repressor active, operon off; no transcription for lactose enzymes n lactose present: repressor inactive, operon on; inducer molecule inactivates protein repressor (allolactose) n transcription is stimulated when inducer binds to a regulatory protein Def: Unit of genetic function consisting of coordinately related clusters of genes with related functions (transcription unit) campbellbiology ANIMATON!