Chapter 19 Genetic Code species to another Overview Concept 19 1 Genes can be transcribed and translated after being transplanted from one Transgenic Plants Genetically Modified plants Bacteriophages Phages viruses that can infect and set in motion a genetic take over of bacteria such as E Coli Viruses consists of a nucleic acid surrounded by a protein coat Discovery of Viruses leaves a mosaic coloration Tobacco mosaic disease stunts the growth of tobacco plants and gives their 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 Viruses 1 Nucleic Acid Contains viral genes Can be single or double stranded DNA or RNA 2 Capsid Protein coat that surrounds the nucleic acid viral genome Capsomeres Protein sub unit building blocks that make up capsid 3 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 a combination 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 ends with the death of host cells Produces new phages and lyses breaks open host s cells wall releasing Virulent phage only uses lytic cycle to reproduce Restriction Enzymes Recognize and cut up certain phage DNA in Lytic Cycle the progeny virus 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 apparatus membrane or Host cell s plasma membrane RNA as viral material genome to DNA Retro viruses Use the enzyme Reverse transcriptase to copy RNA 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 DNA 1 Mutations Creates adaptive Changes in proteins 2 Genetic Recombination Transfers DNA from one bacterium to another a Transformation bacterial cell takes up DNA from dead cells outside and combines it with its own DNA b Transduction infecting bacterial virus phage introduces c Conjunction transfer of specific plasmids from one DNA from previous hosts bacterium to another 3 Rearrangement of Transposons bacterial DNA segments that move within DNA molecule affects overall gene expression
View Full Document
Unlocking...