In this article we will discuss about the meaning of transformation.
Transformation is the process of adding a foreign DNA fragment from a donor genome into genome of a recipient cell. The donor fragment passes through the cell membrane of the recipient cell (which may or may not belong to the same species) and becomes incorporated into the latter’s genome through recombination. Transformation is detected by the presence of new cell phenotypes in the recipient cell’s progeny.
The actual process of transformation is achieved in at least 3 steps as follows:
(a) Interaction between a transforming DNA fragment and the recipient bacterium. For successful transformation of a Pneumococcus cell the DNA fragment must have a minimal size of 800 nucleotide pairs; for Bacillus 16000 nucleotide pairs are necessary.
The number of DNA fragments which can interact with a recipient cell is about 10, as these many receptor sites are present on the cell membrane. The recipient cell must be physiologically competent to receive a donor DNA fragment. This state of competence is acquired during the brief period when the recipient cells are dividing at a maximal rate.
(b) The next step involves movement of DNA fragment in the recipient cell cytoplasm by association with an enzyme system. At the time of its initial contact with the recipient cell, the donor DNA fragment is double stranded; but inside the recipient cell it becomes single stranded.
(c) Finally, the single stranded donor DNA gets covalently incorporated into the double stranded recipient genome and is replicated along with the host cell chromosome.