GEN MICROBIOLOGY BIOL 2051
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This 8 page Class Notes was uploaded by Charles Kohler on Tuesday October 13, 2015. The Class Notes belongs to BIOL 2051 at Louisiana State University taught by K. Sullivan in Fall. Since its upload, it has received 8 views. For similar materials see /class/222793/biol-2051-louisiana-state-university in Biological Sciences at Louisiana State University.
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Date Created: 10/13/15
Chapter 9 Gene Transfer Mutations and Genome Evolution 0 DNA sequence is not static doesn t stay exactly the same happens bc Horizontal gene transfer Transformation Conjugation Transduction Another reason for non static is bc of Mutations Or deletions how serious depends on what is deleted Insertions 0 Effects of Gene Transfer Spreads useful genes among bacteria one bacteria has some great genes and it can shares those genes with another bacterium Good Antibiotic resistance genes Spread wherever antibiotics are overused Like in hospitals and farms Good Pathogenicity stands Encode genes for cell to act as a pathogen Difference between typical E coli in gut and pathogenic Ecoli 0157H7 Good Genes to degrade special metabolitesoil spills Mechanisms of horizontal gene transfer Transformation Transduction Conjugation Transformation competent cell picks up free DNA from the environment get from when other cells lyse Some cells are naturally competentBacillius Some cells can be made competent we can make them competent in the lab by Salt treatment the salts with neutralize the negative charge outside of cells DNA negative and wont repel each other Electroporation electrical shock opens pores in cell membrane DNA enters through pores If free DNA isn t incomorated into 39 it will be degraded into cln Free DNA can t replicate on its own Transduction 7 Bacterial DNA is transferred from one bacterium to another by a Virus Bacteria phage injects DNA into host DNA is packaged into Viral capsid Normally M DNA is packaged Rarely bacterial DNA is packaged by M DNA is transferred to new host Can bring new bacterial genes to host Generalized transduction During Viral infection random pieces of bacterial DNA are accidentally packaged into Viral capsid Any part of the host chromosome can be transferred to a recipient cell Specialized transduction only specific ismall portions of the bacterial chromosome can be transferred to a recipient Donor DNA is either incorporated into recipient chromosome or degraded Specialized transduction example Lambda bacteriophage which infects Ecoli integrates into E 601139 between gal amp bio genes so lambda is inserted btwn to areas of the cell Sometimes lambda DNA excises incorrectl and brin s ad39acent host enes either gal or bio With it Conjugation mating copy of a plasmid is transferred from one cell to another by cell to cell contact Plasmid extrachromosaomal DNA usually circular that replicates independently of the host chromosome Contact between bacteria is first made with pilus pilus brings the cells together Cells are then drawn together to form a mating pair for actual transfer of DNA F fertility plasmid One type of plasmid that can be copied amp transferred to new cell R resistance plasmid carries antibiotic resistance genes Formation of an Hfr F plasmid can sometimes integrate into the host chromosome Hfr high frequency recombinants 7 entire plasmid has integrated into the bacterial chromosome Conjugation can then lead to transfer of large regions of the host chromoso e a potentially form a new plasmid Ithink fax k F formation next thing that happens The F plasmid can be excised form the chromosome l Sometimes it is excised intact F Other times some of the chromosome is excised along with the F plasmid F F prime 7 F plasmid plus chromosomal DNA l Recombination o In all these processes conjugation transformation transduction a piece of DNA enters a bacterial cell This new DNA can replace a portion of the chromosomethis is recombination Donor DNA must be very similar homologous 1 to recipient DNA for recombination to occur Requires specific recombination proteinsRecA RecBCD RuVAB EX If donor DNA has 16102 gene it would replace the 16102 gene in the recipient chromosome Recipient Donor I I 1 Mobile Genetic Elements 39 Chromosome sequence is not xed 39 T 39 39 elements pieces of genetic material that can iust insert quot into genetic material insert into chromosome 39 Found in all species 39 Can jump from one site to another 39 Nonreplicative transpositionnot replication just moving from one place to another 39 Can copy to a new site 39 Replicative transposition this one copies Mutations amp Mutants Mutation change in DNA sequences Mutant organism that has a mutation Genotype genetic makeup of an organism Designated by 3 lowercase letters followed by a capital letter All 4 are italicized or underlined lacZ can make enzyme betagalactosidase plus sign Mutant lacZ Change in DNA sequence in that gene minus Sign Phenotype observable prperties of a strain lSt letter is capitalized not italicized Phenotype of a lacZ strain is LacZ Even if genotype of a mutant is different from the parental strain they can have the same phenotype Mutations Point mutation change in a single base pair can cause a single amino acid change in a polypeptide or no change at all depending on the condon involved 39 Transition purine gt purine or pyrimidine gt pyrimidine 39 Transversion purine lt gt pyrimidine more serious Types Silent mutation no change in phenotype Base change doesn t cause amino acid change Missense mutation causes amino acid change Nonsense mutation changes sense codon to nonsense not coded for an amino acid a stop codon codon Larger mutations 39 Insertion of a section of DNA into chromosome 39 Deletion of a portion of the chromosome 39 Inversion Flipping a portion of chromosomeso its backwards form were it used to be Deletions amp insertions of bases cause more serious changes in the DNA including Frame shifts mutation and often result in loss of gene function Frame shift mutation genetic code is normally read 3 bases at a time 1 codon at a time If reading begins at 2quotd or 3rd base of a codon instead of 1st results in reading frameshift Mutagens Cause Mutations 39 Electromagnetic radiation 39 Xrays gamma rays gt The Hulk 39 UV light gt skin cancer 39 Spontaneous change in N base structure 39 Chemicals 39 Analogs ofbases 39 Basemodifying chemicals 39 Intercolators insert between bases 39 Cause frameshift mutations DNA Repair 39 Mismatch repair 39 Mispaired base cut out of strand 39 Strand without methyl groups is newer 39 Assumed to be in error strand without the methyl group Thymine dimers Induced by UV light Cut out by UvrABC complex nucleotide excision repair or photo reactivation photolyase repairs bases without excision Damaged Bases Excised by speci c enzymes Replaced by DNA Polymerase I Recombinational repair Occurs just after strand has been copied Undamaged strand is copied replaces damaged strand Catalyzed by RecA recombinase SOS Repair Extensive DNA damage inactivates LexA Activation of many repair genes Rapid polymerization of DNA Errorprone but better than no repair
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