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20 Cards in this Set
- Front
- Back
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3 mechanisms of horizontal gene transmission
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1. Transduction (generalized or specialized)
2. Transformation 3. Conugation |
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Generalized transduction
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Phage infect donor bacteria with phage DNA
Small fraction of phages synthesized will package bacterial DNA by mistake Donor lysis Second infection with phages on recipient bacteria Some bacteria will be infected by phage carrying that bacterial DNA |
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Specialized transduction
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Lysogenic prophage DNA packaged into phages along with accidental bacterial DNA immediately adjacent to the prophage
Donor cell lysis Second infection Chimeric (phage + bacterial) DNA injected into bacterial recipient Temperate phages only Site of integration limits what type of DNA you pick up |
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Transformation
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simply taking up information from the environment into the bacteria
Gram positive: binding, fragmentation, transport (uptake) Gram neg: binding, fragmentation, uptake into periplasm, transport (final uptake) |
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Conjugation
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Bacterial mating
Donor connects with recipient (mating jxn) Substrate processing and transport Plasmid regeneration and cell dissociation *Unidirectional: donor to recipient *Gram neg uses a pilus *Conservative: information that is donated is also copied; not lost in donor cell |
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Domains of life
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Archaea
Bacteria Eukarya |
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Prokaryotes
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Bacteria
Archaea No true nucleus; no visible MB organelles |
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Eukaryotes
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Fungi- uni (yeast) or multicellular (molds)
Protozoa- unicellular Helminths- multicellular; macroscopic |
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Homologous recombination
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Way for bacterial DNA to get incorporated:
pairing of similar DNA sequences over 100s to 1000s of bps Ex. incorporation via horizontal gene transfer; genome rearrangements |
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Site-specific recombination
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Specific, short (10s bp) DNA sites
Ex. prophage excision/integration (typically temperate prophages) |
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Non-homologous recombination
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No DNA sequence similarity at recombination sites
Ex. transposition |
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Recombination
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Way to combine different DNA molecules
1. Homologous 2. Site-specific 3. Non-homologous |
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Transposable genetic elements
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Target DNA inserted as essentially random locations
Can carry antibiotic resistance Can interrupt host gene expression Can change expression pattern of neighboring genes Genome reorganization Insertion sequences Composite sequences Replicative transposition |
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Insertion sequences
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Simplest transposon
Overall length about 1-2 kbp Can catalyze their own movement from one piece of DNA to another |
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Composite transposons
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Non-replicative or replicative
Flanked by two insertion sequence elements (may or may not be exact replicas) Instead of each IS element moving separately, the entire length of DNA spanning from one IS element to the other is transposed as one complete unit. Composite transposons will also often carry one or more genes conferring antibiotic resistance. |
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REplicative transposition
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*Transposition is a form of non-homologous recombination*
Donor DNA and target DNA fuse; replication occurs through the transposon; now both target DNA and donor DNA have the transposon Effectively copying the transposon into the target |
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Collective genome
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Core genome + flexible gene pool (20-30%)
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Core genome
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homogeneous G+C content
All essential fxns |
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Flexible gene pool
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Varying G+C content of foreign origin
Prophage Mobile genetic elements (Insertion sequences, transposons) Genomic islands |
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GEnomic islands
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Contiguous block of bacterial genes that encode pathogenesis functions and are of foreign origin
Could encode: Pathogenesis (secretion, adhesion, invasion, toxins, siderophores) Symbiosis Metabolism Drug resistance |
