CH. 9 Mechanisms of Horizontal Gene Transfer Flashcards
What is recombination? What is the protein for it?
The repairing of damaged DNA and acquiring of new genes via horizontal gene transfer mechanisms:
-Degrading DNA (use as food)
-Recombine with chromosome
-Co-exist
RecA is a major recombination protein where it scans DNA for and aligns homologous regions
Describe the horizontal gene transfer of transformation (gram-positive, gram-negative, natural, and artificial)
Uptake of “naked” DNA from the environment.
Gram-Positive Bacteria:
-Natural transformation
-Establishment of competence factors to take up DNA
-Establishment of transformasome (takes up a single DNA strand to combine to new chromosomes for new genes)
Gram-Negative:
-Natural transformation
-Production of type IV sex pilus that attaches to bring external DNA fragments into the cell
Artificial Transformation: induce competence in cells by the addition of chemicals or electrical charges (ex. heat shock)
Natural Transformation: competent cells are able to take up DNA
*Competence factors (CF) bind sensor protein to initiate sigma factor expression to then promote the expression of operons involved in the expression of proteins for transformation
What is quorum sensing?
The regulation mechanism of gene expression in response to fluctuations in cell density
Describe the horizontal gene transfer of conjugation and conjugation-specific genes
Cell-to-cell contact & transfer of DNA via sex pilus that is facilitated by F factors (fertility factors) and are also known as transferable/conjugative plasmids
Conjugation-specific genes:
-tra genes (transfer genes)
-sex pilus
-relaxasome (facilitates bridging of the cell and transferring of DNA)
-oriT (for transfer)/oriV (used when not conjugating)
Describe the horizontal gene transfer of F factors, F’ (F prime) factors, and Hfr strains within conjugation
F factors are known as fertility factors plasmids that facilitate conjugation for the transferring of plasmids
F+ cell contains the plasmids with transfer gene (tra) and oriT. They are known as the donor cells
F- cell is the recipient cell, and it can remain as a plasmid or be integrated into a cell via recombination to turn into an Hfr cell within areas of homology between plasmid & chromosome
Hfr (high-frequency recombination) strains are able to transfer PART of their chromosomes via conjugation. HOWEVER, Hfr and F- mating involves the F- recipient gaining the chromosomal genes, but it REMAINS AS A F- due to the conjugational pairing not occurring long enough to pass the tra genes (fertility genes) to the F- recipient
F’ (F prime) factor formation occurs with an error in the excision of integrated F factor, containing some host DNA yet have extra genes expressed (known as partial diploid)
Describe the horizontal gene transfer mechanisms and components involved in transduction (difference between generalized and specialized transduction). What other process of horizontal gene transfer does specialized transduction resemble and why?
The transfer of DNA via a viral immediate where bacteriophage/virus contain bacterial DNA to infect a new host and transfer the DNA
General Transduction: any genes can transfer between cells
Specialized Transduction: transfer of a few closely linked genes and represents F’ (F prime) factor conjugation due to gaining an extra copy of genes (partial diploid)
What is transposition and how does it operate? What is conjugative transposition?
Transposition is the process of mobilizing the transposable element within or between DNA molecules
-Transposons (transposable elements) contain transposase genes that catalyze the transfer or copying of a unit from one DNA to another by either nonreplicative (cut & paste) or replicative (copy & paste) transposition
-Insertion sequence (transposable element) consists of transposase genes flanked by inverted repeat sequence that are targets for transposase
Conjugative transposition is the transfer of transposon (transposable element) to another cell via conjugation
What is a partial diploid cell?
A cell acquiring an extra copy of a chromosomal gene and can be in result of conjugation with an F’ cell or specialized transduction
