Overview of Conjugation Flashcards
Describe the experiment that demonstrated that sexual recombination could take place in bacteria.
Was achieved by Lederberg and Tatum. Working with double auxotrophs for His and Trp, found that revertants were occurring i.e, bacteria were becoming phototrophic again, and sexual recombination must be taking place.
Davis U-tube experiment - using a U-tube showed that sexual recombination i.e conjugation requires contact.
Give a brief overview of how conjugation takes place in bacteria - E.coli.
Conjugation occurs in plasmids. Contact between two cells occurs via the pillus. At the OriT site the enzyme, Nicase, nicks the plasmid leaving a 3’ OH group which can be extended through DNA synthesis. The pillus pulls the two cells closer together, and a pore complex forms. Rolling circle transfer occurs, whereby DNA replication at the 3’ OH pushes the ssDNA into the recipient cell, which is then converted to dsDNA. Occurs between F+ (donor) and F- (recipient)
What is horizontal gene transfer in bacteria?
Whereby an organism acquires genes directly from another cell and incorporates them into its genome, is critical in bacteria adaptions, and is distinct from vertical gene transfer (i.e passing genes to offspring/ next generation)
Provide a brief explanation of conjugative chromosome transfer.
Donor cells are Hfr. Whereby the F plasmid is integrated into the chromosome. Same mechanism as standard plasmid conjugation, however when it comes to chromosomal transfer, the entire chromosome is not transferred. Part of the integrated F plasmid, and part of the chromosome are transferred, but due to the instability of the mating pore complex not everything is transferred.
