Extrachromosomal replication & plasmids Flashcards
Organisms from which domains are capable of horizontal gene transfer?
Archaea and Bacteria
What is Transformation?
An event of uptake of exogenous DNA by a bacterial cell from the surrounding through the cellular membrane.
What is the requirement from the recipient bacterium for a successful transformation?
A bacterium needs to be competent to absorb external DNA, which in nature may come as a response to a difficult environmental situation.
What is Transduction?
An event of DNA transfer to the recipient bacterium via phage vector.
Which of the 3 horizontal gene transfer mechanisms requires the direct contact between 2 bacterial cells?
Conjugation
What is conjugation?
An event of unidirectional gene transfer, as a result of a direct connection between the donor cell and the acceptor cell.
What is the fertility factor?
A measure of the ability to donate one’s genes.
F+ - male - donor
F- - female - acceptor
What is the F episome?
F episome is a plasmid that carries the fertility factor. It can be conjugated from a donor to acceptor cell. It also can integrated into the chromosomal DNA of the host cell.
What genes does tra region on F episome carry?
tra carries the genes for conjugative functions of F episome ( DNA replication and transfer, pilus formation and T4SS)
Describe the Transfer of F episome by conjugation.
First, pilus forms between 2 cells and retracts pulling them together. An intracellular bridge is formed, the DNA is nicked by relaxosome at the oriT and a rolling circle replication starts. Relaxase unwinds the coding strand and pulls the 5’ end through the pilus(T4SS), by contacting the transferosome through mediating proteins TraD and TraM. The transferosome-relaxosome complex is pulled through to the acceptor cell, where a complementary strand starts being synthesized. The transfer is terminated until random breakage of the pilus occurs.
What are Hfr strains?
Hfr strains are bacterial strains of high recombination frequency, which is a result of the recombination of the chromosomal DNA exchanged via conjugation. Integrated F episomes initiate transcription during conjugation from oriT and continue to transcribe the DNA including chromosomal DNA until interrupted. Due to the part of chromosomal DNA, the recipient does not develop a fucntional f episome and keeps its F- phenotype. The partial chromosome cannot replicate and thus it is either lost or it recombines with the recipient’s chromosome creating a new phenotype.
What are R factors?
Plasmids carrying the resistance to various antibiotics, many of which can be conjugated.
What are Bacteriocins?
Substances secreted by bacteria that inhibit the growth of closely related bacterial strains
What are the most important phenotypes conferred by plasmids in prokaryotes?
1) Antibiotic Production
2) Conjugation
3) Antibiotic/toxic metal resistance
4) DNA restriction & modification
5) Bacteriocin production & resistance
