Cell Transformation

Transforming Bacteria During transformation, a cell takes in DNA from outside the cell. This external DNA becomes a part of the cell’s DNA. Example: Griffith’s experiments with bacteria Foreign DNA is joined to a “plasmid” – a small, circular DNA molecule found in some bacteria Why plasmids are useful for DNA transfer: Have a DNA sequence that acts as an origin of replication Carry a genetic marker – a gene that makes it possible to distinguish bacteria that carry the plasmid and foreign DNA from those that do not.

In the lab… https://www.youtube.com/watch?v=iDfEVhePDPM

The Result!

Transforming Plant Cells Researchers use a bacteria that transmits a plasmid into plant cells which would normally cause a tumor. The tumor-causing gene is inactivated, and a piece of foreign DNA is inserted into the plasmid. The recombinant plasmid can then be used to infect plant cells. DNA is taken up by plant cells either by: 1) removing the cell wall, or 2) injecting it directly into the cells If successful, the recombinant DNA is integrated into one of the chromosomes of the plant cells.

Transforming Animal Cells Sometimes DNA can be injected into the nucleus (since it is larger), and enzymes will insert it into the chromosomes. Marker genes are used to identify which cells have taken up the DNA. New procedure: “knock out” – DNA molecules are constructed to recombine with specific sequences in the host chromosome. The host target gene between those sequences is replaced with the new gene. (This has helped identify functions of genes.)