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Transformation, Transduction and Transfection –Gene transfer methods
The three very effective modes of gene transfer Transformation, Transduction and Transfection observed in bacteria fascinated the scientist leading to the development of molecular cloning. The basic principle applied in molecular cloning is transfer of desired gene from donor to a selected recipient for various applications in the field of medicine, research, gene therapy with an ultimate aim of beneficial to the mankind.

Transformation: Transformation is the naturally occurring process of gene transfer which involves absorption of the genetic material by a cell through cell membrane causing the fusion of the foreign DNA with the native DNA resulting in the genetic expression of the received DNA. Transformation is usually a natural method of gene transfer but as a result of technological advancement originated the artificial or induced transformation. Thus there are two types called as natural transformation and artificial or induced transformation. In natural transformation, the foreign DNA attaches itself to the host cell DNA receptor and with the help of the protein DNA translocase it enters the host cell. The presence of nucleases restricts the entry of two strands of the DNA, destroys a single strand thus allowing only one strand to enter the host cell. This single stranded DNA mingles with the host genetic material successfully.

The artificial or induced method of transformation is done under laboratory condition which is either a chemical mediated gene transfer or done by electroporation. In the chemical mediated gene transfer, the cold conditioned cells in calcium chloride solution are exposed to sudden heat which increases the permeability of the cell membrane allowing the foreign DNA. The electroporation method as the name indicates, pores are made in the cell by exposing it to suitable electric field, allowing the entry of the DNA. The opened up portions of the cell are sealed by the ability of the cell to repair.

Transduction: In transduction, a media like virus is required between two bacterial cells in transferring genes from one cell to the other. Researchers used virus as a tool to introduce foreign DNA from the selected species to the target organism. Transduction mode of gene transfer follows either a lysogenic phase or lytic phase. In the lysogenic phase, the viral (phage) DNA once joining the bacterial DNA through transduction stays dormant in the following generations. The induction of lysogenic cycle by an external factor like UV light results in lytic phase. In lytic phase, the viral or phage DNA exists a s a separate entity in the host cell and the host cell replicates viral DNA mistaking it for its own DNA.As a result many phages are produced within the host cell and when the number exceeds it causes the lysis of the host cell and the phages exits and infects other cells. As this process involves existence of both the genome of the phage and the genome of the bacteria in the same cell, it may result in exchange of some genes between the two DNA. As a result, the newly developed phage leaving the cell may carry a bacterial gene and transfer it to the other cell it infects. Also some of the phage genes may be present in the host cell. There are two types of transduction called as generalized transduction in which any of the bacterial gene is transferred via the bacteriophage to the other bacteria and specialized transduction involves transfer of limited or selected set of genes.

Transfection: One of the methods of gene transfer where the genetic material is deliberately introduced into the animal cell in view of studying various functions of proteins and the gene. This mode of gene transfer involves creation of pores on the cell membrane enabling the cell to receive the foreign genetic material. The significance of creating pores and introducing the DNA into the host mammalian cell contributed to different methods in transfection. Chemical mediated transfection involves use of either calcium phosphate or cationic polymers or liposomes. Electroporation, sonoporation, impalefection, optical transfection, hydro dynamic delivery are some of the non chemical based gene transfer. Particle based transfection uses gene gun technique where a nanoparticle is used to transfer the DNA to host cell or by another method called as magnetofection. Nucleofection and use of heat shock are the other evolved methods for successful transfection.
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Transformation, Transduction and Transfection –Gene transfer methods - by priyasaravanan_1406 - 10-12-2012, 09:20 PM
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