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CHAPTER 18 Microbial Models: The Genetics of Viruses and Bacteria Size Averages Eukaryotic 10 um. Bacteria 1 um. Viruses .1um. Respiratory infections & pink eye The human Papilloma virus causes warts and cervical cancer double stranded circular DNA Adenovirus causes respiratory infections and pink eye Bacteriophages Simplified viral reproductive cycle double stranded DNA Lytic cycle of a T4 phage Parts selfassemble The lysogenic and lytic reproductive cycles of phage lambda a temperate phage The reproductive cycle of an enveloped virus with a single stranded RNA genome but not a retrovirus Structure and Life Cycle of an HIV virus a retrovirus HIV infection Ebola virus-too virulent? Deer mouse Hanta virus Vaccines- ”harmless” variations of the virus that initiate the immune system to form memory T-cells and B-cells Synthetic vaccines-made from other viruses usually the smallpox virus with recombinant DNA technology, no possible infection Tobacco mosaic virus Tobacco mosaic virus Viroids Tiny molecules of naked circular RNA. They do not encode proteins but they can replicate in host cells using the hosts cells enzymes. They seem to only affect plants. Some how they disrupt metabolism of the plants and cause errors in regulation of protein synthesis. Affects tomatoes, potatoes, and palm trees Prions Infectious protein molecules that can somehow replicate in cells. They cause degenerative brain diseases. They cause scrapie in sheep, “mad cow disease” or bovine spongiform encephalitis, and Creutzfeldt Jacob disease in humans. Cause the normal form of a protein to fold up wrong and thus become a prion. RESTRICTION ENZYMES RESTRICTION ENDONUCLEASES Produced by bacteria for protection from viruses, they cut DNA at specific recognition sites and prevent it from taking over the cell. They can all be called endonucleases. They often make uneven cuts that leave short single-stranded pieces on each end called “sticky ends” How do bacteria keep their own DNA from being cut by their restriction enzymes? Methylate their restriction sites How are restriction enzymes used in recombinant DNA technology? Normal without an F+ episome Replication of the bacterial chromosome begins at one origin and continues in both directions Detecting genetic recombination in bacteria So, what happened? Conjugation and recombination in E. coli Plasmids-small rings of DNA that contain 2 - 30 genes and can replicate on their own when in a cell by rolling circle replication R plasmids contain genes for antibiotic resistance How could several genes for antibiotic resistance end up on the same plasmid? Transposons Conjugation and recombination in E. coli Conjugation and recombination in E. coli F-pili Insertion of a transposon and creation of direct repeats Anatomy of a composite transposon The trp operon a Repressible Operon Tryptophan absent, repressor inactive, operon on The trp operon a Repressible Operon Tryptophan present, repressor active The trp operon a Repressible Operon Tryptophan present, repressor active, operon off The lac opreron: an inducible operon for enzymes that are only needed occasionally What would happen if a mutation to the regulator gene produced a defective repressor protein? What would happen to the levels of the mRNA and the enzymes after all available lactose was digested? Smallpox Measles Measles Polio Hepatitus Killed 300,000 worldwide Began in 1918 Herpes E. coli DNA plasmids
