It is the term used to describe the introduction of foreign material into eukaryotic cells. This typically involves opening transient pores or 'holes' in the cell plasma membrane to allow uptake of material. There are various methods of introducing foreign DNA into a cell. One of the cheapest (and least reliable) is chemical transfection by calcium phosphate. HEPES-buffered saline solution (HeBS) containing phosphate ions is combined with a calcium chloride solution containing the DNA to be transfected. When the two are combined, a fine precipitate of calcium phosphate will form, binding the DNA to be transfected on its surface. The suspension of the precipitate is then added to the cells to be transfected (usually a cell culture grown in a monolayer). By a process not entirely understood, the cells take up some of the precipitate, and with it, the DNA.
Transfection is frequently carried out by mixing a cationic lipid with the material to produce liposomes which, after application, fuse with the cell plasma membrane and deposit their cargo inside.
Other methods of transfection include electroporation, that is a significant increase in the electrical conductivity and permeability of the cell plasma membrane caused by an externally applied electrical field.
Pores are formed when the voltage across a plasma membrane exceeds its dielectric strength. If the strength of the applied electrical field and/or duration of exposure to it are properly chosen, the pores formed by the electrical pulse reseal after a short period of time, during which extracellular compounds have a chance to enter into the cell. However, excessive exposure of live cells to electrical fields can cause apoptosis and/or necrosis the processes that result in cell death. |