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Chapter 19-Genetic CodeGenes can be transcribed and translated after being transplanted from one species to anotherTransgenic Plants: Genetically Modified plants-OverviewBacteriophages (Phages): viruses that can infect and set in motion a genetic take over of bacteria, such as E.Coli-Concept 19.1Viruses consists of a nucleic acid surrounded by a protein coat-Discovery of VirusesTobacco mosaic disease stunts the growth of tobacco plants and gives theirleaves a mosaic coloration1883, Adolf Mayer discovered that he could transmit the disease by rubbing infected sap onto a healthy plant1890, Dimitri Ivanowsky passed the sap through a filter designed to remove bacteria, the filtered sap still contained the diseaseLater Matinus Beijerinck discovered that the infectious agent in the sap was able to reproduce only within the host cell that it infectedCredited with the concept of the Virus1935, Wendell Stanley confirmed this by crystalizing the infectious particle, Tobacco Mosaic Virus, (TMV).-Structure of Viruses1) Nucleic Acid: Contains viral genesCan be single or double stranded DNA or RNA2) Capsid: Protein coat that surrounds the nucleic acid (viral genome)Capsomeres: Protein sub-unit building blocks that make up capsid3) Membranous envelope: Found only in some virusesViral Envelope: Membranous envelopes that help virus infect host, surround capsid of influenza virusViral envelopes derived from host cell’s membrane, contain acombination of viral and host cell moleculesBacteriophages (phages): Viruses that infect bacteriaMost complex capsids found among virusesPhages have elongated capsid head that encloses their DNAProtein tail attaches phage to the host cell and injects the phage DNA inside-Concept 19.2: Viruses replicate only in host cellsViruses are obligate intracellular parasites, which means that they can replicate only in host cellsEach virus has a host range (Broad: West Nile, Narrow: Measles) limited number of host cells it can infect.Host specify results from evolution of viral recognition system of host cell receptor molecules-Replicative cycles of PhagesLytic Cycle, Lysogenic Cycle-Lytic CycleLytic Cycle: ends with the death of host cellsProduces new phages and lyses (breaks open) host’s cells wall, releasing the progeny virusVirulent phage: only uses lytic cycle to reproduceRestriction Enzymes: Recognize and cut up certain phage DNA, in bacteria.-Lysogenic CycleLysogenic Cycle: replicates phage genome with out killing cellProphage: Viral DNA is incorporated into the host cell’s chromosomesEnvironmental signal can trigger virus to enter lytic modeTemperate phages: use lysogenic and lytic cycle-Replicative cycles of animal virus2 factors to classify virusesDNA or RNA Single Strand or Double Strand-Viral EnvelopesViral glycoproteins on the envelope of virus bind to specific receptor molecules on the surface of host cellViral envelopes: Host’s nuclear envelope replace by Golgi apparatusmembrane or Host’ cell’s plasma membrane.-RNA as viral materialRetro viruses: Use the enzyme Reverse transcriptase to copy RNA genome to DNAHIV is the retro virus that causes AIDS, targets white blood cellsProvirus: viral DNA that is integrated into the host genome, permanent.-Prokaryotic GeneticsMost prokaryotic genes are located in circular DNABacteria sometimes change nucleotide sequences DNA1) Mutations: Creates adaptive Changes in proteins2) Genetic Recombination: Transfers DNA from one bacterium to anothera. Transformation: bacterial cell takes up DNA from dead cells outside and combines it with its own DNAb. Transduction: infecting bacterial virus (phage) introduces DNA from previous hostsc. Conjunction: transfer of specific plasmids from one bacterium to another.3) Rearrangement of Transposons (bacterial DNA segments that move within DNA molecule) affects overall gene


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FSU BSC 2010 - Chapter 19

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