Chapter 19-Genetic CodeGenes can be transcribed and translated after being transplanted from one species to anotherTransgenic Plants: Genetically Modified plants-OverviewBacteriophages (Phages): viruses that can infect and set in motion a genetic take over of bacteria, such as E.Coli-Concept 19.1Viruses consists of a nucleic acid surrounded by a protein coat-Discovery of VirusesTobacco mosaic disease stunts the growth of tobacco plants and gives theirleaves a mosaic coloration1883, Adolf Mayer discovered that he could transmit the disease by rubbing infected sap onto a healthy plant1890, Dimitri Ivanowsky passed the sap through a filter designed to remove bacteria, the filtered sap still contained the diseaseLater Matinus Beijerinck discovered that the infectious agent in the sap was able to reproduce only within the host cell that it infectedCredited with the concept of the Virus1935, Wendell Stanley confirmed this by crystalizing the infectious particle, Tobacco Mosaic Virus, (TMV).-Structure of Viruses1) Nucleic Acid: Contains viral genesCan 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 virusesViral Envelope: Membranous envelopes that help virus infect host, surround capsid of influenza virusViral envelopes derived from host cell’s membrane, contain acombination of viral and host cell moleculesBacteriophages (phages): Viruses that infect bacteriaMost complex capsids found among virusesPhages have elongated capsid head that encloses their DNAProtein tail attaches phage to the host cell and injects the phage DNA inside-Concept 19.2: Viruses replicate only in host cellsViruses are obligate intracellular parasites, which means that they can replicate only in host cellsEach 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 PhagesLytic Cycle, Lysogenic Cycle-Lytic CycleLytic Cycle: ends with the death of host cellsProduces new phages and lyses (breaks open) host’s cells wall, releasing the progeny virusVirulent phage: only uses lytic cycle to reproduceRestriction Enzymes: Recognize and cut up certain phage DNA, in bacteria.-Lysogenic CycleLysogenic Cycle: replicates phage genome with out killing cellProphage: Viral DNA is incorporated into the host cell’s chromosomesEnvironmental signal can trigger virus to enter lytic modeTemperate phages: use lysogenic and lytic cycle-Replicative cycles of animal virus2 factors to classify virusesDNA or RNA Single Strand or Double Strand-Viral EnvelopesViral glycoproteins on the envelope of virus bind to specific receptor molecules on the surface of host cellViral envelopes: Host’s nuclear envelope replace by Golgi apparatusmembrane or Host’ cell’s plasma membrane.-RNA as viral materialRetro viruses: Use the enzyme Reverse transcriptase to copy RNA genome to DNAHIV is the retro virus that causes AIDS, targets white blood cellsProvirus: viral DNA that is integrated into the host genome, permanent.-Prokaryotic GeneticsMost prokaryotic genes are located in circular DNABacteria 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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