8.8 conjugation

chromosomal transfer

-less common than plasmid transfer and involves Hfr cells (meaning high frequency of recombination) -are strains in which the F plasmid has integrated into the chromosomes by homologous recombination, which is rare. -note the process is reversible.

plasmid transfer

-most frequently trf to other cells by conjugation -these DNA molecules are replicons, so they can be replicated inside the cells.

The F plasmid encodes several proteins req for conjugation including

F pilus (AKA sex pilus)

when integrated F plasmid DNA is excised from the chromosome, an excision error can remove chromosomal DNA along with the F plasmid DNA, creating a plasmid called?

F'

In bacterial conjugation, all F+ donor cells are high frequency recombination (Hfr) cells. T or F

False

In bacterial conjugation, a donor cell with an F ___?___ located in the cytoplasm is considered F+

PLASMID

when an Hfr cell trf chromosomal DNA, the 1st step involves making an F pilus? T or F

TRUE

F donors

when an error occurs during excision, and a piece of the bacterial chromosomes is removed along with the F plasmid DNA. this action brings a chromosomal fragment into the F plasmid producing a plasmid call F' (F prime)

plasmid transfer involves :

1. making contact. -the F pilus contacts the recipient F- cell 2.initiating transfer -the pilus retracts and pulls the donor and recipient cells together. and cut at the origin of transfer 3.transferring DNA -a single strand of the F plasmid is transferred to the recipient cell; its complement is synthesized as it enters the cell. the strand transferred by the donor is replaced, using the remaining strand as a template for DNA synthesis. 4.transfer complete -both the donor and recipient cells are F+ and synthesize the F pilus.

refers to DNA transfer req. cell to cell contact

conjugation

conjugative plasmids

direct their own trf from donor to recipient cells. the most thoroughly studied examples is F plasmid (F stands for fertility) of E. coli. -E.coli cells that contain the F plasmid are designated F+ -whereas those that do not are F-

chromosomal DNA is trf with F plasmid DNA in an Hfr cell because

the plasmid DNA is integrated into the chromosome in these cell

conjugation

is a complex process that requires contact between donor and recipient bacterial cells. -gram (+) & gram (-) can both trf DNA this way, but the process is quite diff in the two groups. -both plasmid DNA and chromosomal DNA can be transferred from one cell to another by conjugation.

chromosomal DNA that is transferred from an Hfr cell but does not integrate into the recipient's chromosome

is degraded

in bacterial conjugation, F+ donor cells are high frequency recombinant (Hfr) cells when the F ___?___ is integrated into the chromosome

plasmid