- Natural transformation = uptake of DNA fragments from medium surrounding cell. Requires specific proteins in cell membrane, energy.
- Only found naturally in certain cells; e.g. Pneumococcus, Hemophilus, etc. Not found in E. coli.
- Why did this evolve? Maybe as way to scrounge DNA from dead cells, save trouble of having to make nucleotides from scratch.
- Cells that can take up DNA are said to be competent. Requires induction of several genes. Typically occurs during exponential growth, shuts off in stationary phase.
- Artificial transformation = laboratory technique to enhance DNA uptake of cells that do not have genetic machinery for transformation.
- Example: treat E. coli with high Ca++ concentrations, then chill. DNA uptake now occurs (though not as well as with naturally competent bacteria).
- Electroporation: pulsed electric fields produce short-lived membrane pores, allows DNA movement (either in or out of cell). Useful way to move small pieces of DNA and plasmids between cells.
- See natural transformation and artificial transformation ("protected" image.)
Sunday, February 17, 2008
Types of Horizontal Gene Transfer
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