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24 Cards in this Set
- Front
- Back
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What is meant by artifical transformation?
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Carried out in the lab using techniques such as: CaCl to render their membranes more permeable to DNA, higher concentrations of DNA, or using plasmids to transfer DNA.
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What DNA sequences and enzymes are required for Homologous Recombination?
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The process is mediated by RecA with the SOS response and can occur b/w any two areas of sequence identity.
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What are the two examples of site specific recombination (from lecture)? Are they RecA mediated?
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1."Inversions"Salmonella Flagellar promoter requires hin, switched on/off produces diff. flagells 2. "Phage integration" lambda attp/E.coli attB uses int enzyme to let phage integrate. 3."Transposition" tramsposons & insertion elements require a transposase but target sites maynot be specific. RecA=no?
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What are the general characteristics of plasmids? What is plasmid copy #?
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Sm.circular replicons (2,000-200,000bp) double strained, nonessential, and there are a # of copies of a plasmid per chromosome( plasmid copy #).
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What does it mean to cure a plasmid?
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Plasmids can be eliminated from host cells in this process. May occur spontaneously or with treatments.
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What are the Conjugative (F)plasmids?
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all have sex pili (for gram-negative cells) responsible for cell attachment and plasmid transfer. Information required for plasmid transfer is located in the tra operon.
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What are the R Factor plasmids?
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Plasmid gene that codes for antibiotic resistance, may be for multiple antibiotics, may be on transposons(mobile units).
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What are the Col plasmids?
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Contains Bacteriocins which kill other bacteria by putting pores in their membranes, degrade DNA RNA (nucleases). "col"=colicin=kills E.coli!
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What are the Metabolic plasmids?
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Carry genes that can degrade(catabolic) substances (toluene,pesticides,sugars), nitrogen fixation(in Rhizobium-cross kingdom), and gall formation
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What are the Virulence plasmids?
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Make the host more pathogenic-better able to reisit host defense or produce toxins. Has adhesins and siderophores(bind Fe)
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Describe the ends and internal genes of Insertion Seq.(IS) and Transposons(Tn).
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They encode for their own movement w/in the genome: IS-small, only has genes for transposition,terminal inverted repeats(15-45bp), transposase. Tn-larger, also have other genes, 2 types of ends:simple w/flanking IR sequences or composite w/ flanking IS elements.
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When a transposon moves does the original copy remain?
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No, it remains in the parental site on the chromosome, while replicated copy inserts at the target DNA.
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Why is the target sequence duplicated?
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So that short, direct-sequence repeats flank the transposon's terminal inverted repeats.
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What is the effect of transposition on the gene with the target sequence?
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Termination, translation stops, new promoters, homologous recombination (deletions/duplications)
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What are the progeny of F+/F- conjugative matings? Of Hfr/F- matings?
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F+/F+; rare F- conversion
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What are F' plasmids?
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Error from Hfr excision bringing nearby DNA. F plasmid w/ some chromosomal DNA. Forms partial diploids
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Can Hfr strains mate with F+ Strains? How do Hfr strains arise?
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No; Hfr (High chromosome transfer rate) strains arise from integration via homologous recombination. Rare F- conversion due to long mating period of 100'; )
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How do genes transfered by these methods (F+,Hfr,etc)become incorporated into the genome?
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?
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What is meant by "transformation" of "competent" cells?
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-taking up naked (yummy) external DNA
-the ability to takeup and maintain naked DNA |
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What are the roles of competence factors and autolysins in the natural transformation of Streptococcus pneumoniae?
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Compentence factors simulate proteins including autolysins which partially digest peptidoglycan in growing bacteria so that the pg can be enlarged.
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How do generalized and specialized transductions differ?
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Generalized-accidental packing of chromosomal DNA, pac site misrecognition, P22 packages 1% of genome and incorp. by homo. recomb.
Specialized-phage excisions take adjacent genes. hybrid att is nonfxn, homo recomb. |
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How can conjugation be used to "map" the chromosome?
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Use Hfr(long mating period) and interupt at set times
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Which is more useful in mapping-generalized or specialized transduction?
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Specialized-it shows precise placement of genes on a chromo by way of Phage att site. Generalized-Cotransduction Freq. means by each other on chromo.
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How does the size of the viral genome limit the resolution of mapping? Which give the finest levels of resolution?
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Size of the genome may take more times to map due to small amount of information that can be transduced. Finest Resolution:Hfr-Transduction-Transformation-Sequencing
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