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24 Cards in this Set

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  • Back
What is meant by artifical transformation?
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.
What DNA sequences and enzymes are required for Homologous Recombination?
The process is mediated by RecA with the SOS response and can occur b/w any two areas of sequence identity.
What are the two examples of site specific recombination (from lecture)? Are they RecA mediated?
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?
What are the general characteristics of plasmids? What is plasmid copy #?
Sm.circular replicons (2,000-200,000bp) double strained, nonessential, and there are a # of copies of a plasmid per chromosome( plasmid copy #).
What does it mean to cure a plasmid?
Plasmids can be eliminated from host cells in this process. May occur spontaneously or with treatments.
What are the Conjugative (F)plasmids?
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.
What are the R Factor plasmids?
Plasmid gene that codes for antibiotic resistance, may be for multiple antibiotics, may be on transposons(mobile units).
What are the Col plasmids?
Contains Bacteriocins which kill other bacteria by putting pores in their membranes, degrade DNA RNA (nucleases). "col"=colicin=kills E.coli!
What are the Metabolic plasmids?
Carry genes that can degrade(catabolic) substances (toluene,pesticides,sugars), nitrogen fixation(in Rhizobium-cross kingdom), and gall formation
What are the Virulence plasmids?
Make the host more pathogenic-better able to reisit host defense or produce toxins. Has adhesins and siderophores(bind Fe)
Describe the ends and internal genes of Insertion Seq.(IS) and Transposons(Tn).
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.
When a transposon moves does the original copy remain?
No, it remains in the parental site on the chromosome, while replicated copy inserts at the target DNA.
Why is the target sequence duplicated?
So that short, direct-sequence repeats flank the transposon's terminal inverted repeats.
What is the effect of transposition on the gene with the target sequence?
Termination, translation stops, new promoters, homologous recombination (deletions/duplications)
What are the progeny of F+/F- conjugative matings? Of Hfr/F- matings?
F+/F+; rare F- conversion
What are F' plasmids?
Error from Hfr excision bringing nearby DNA. F plasmid w/ some chromosomal DNA. Forms partial diploids
Can Hfr strains mate with F+ Strains? How do Hfr strains arise?
No; Hfr (High chromosome transfer rate) strains arise from integration via homologous recombination. Rare F- conversion due to long mating period of 100'; )
How do genes transfered by these methods (F+,Hfr,etc)become incorporated into the genome?
What is meant by "transformation" of "competent" cells?
-taking up naked (yummy) external DNA
-the ability to takeup and maintain naked DNA
What are the roles of competence factors and autolysins in the natural transformation of Streptococcus pneumoniae?
Compentence factors simulate proteins including autolysins which partially digest peptidoglycan in growing bacteria so that the pg can be enlarged.
How do generalized and specialized transductions differ?
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.
How can conjugation be used to "map" the chromosome?
Use Hfr(long mating period) and interupt at set times
Which is more useful in mapping-generalized or specialized transduction?
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.
How does the size of the viral genome limit the resolution of mapping? Which give the finest levels of resolution?
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