The modem biotechnology revolution is based on the understanding and manipulation of the structure of DNA. DNA is a complex organic molecule that directs the synthesis of proteins in all living organisms. Thus, it controls the physical structure, growth, reproduction and function of all living beings. The programme for controlling protein synthesis is coded in the chemical structure of DNA. The discovery of the code, and the synthesis of DNA in test tubes, were important milestones in genetic engineering. However, the foundation of genetic engineering was laid by the discovery, that QNA suppljed from outside is accepted by micro-organisms. DNA thus inserted into the cell en from a micro-organism, enables the cells to make the proteins specified in the codes of the inserted DNA. These new cells can be cultivated or cloned, until a significant number of cells are available. to produce specific, desired protein molecules. -3 However, this is not so easily done. When a foreign DNA molecule enters a cell, spcclal enzymes, called restriction enzymes, rapidly destroy it This problem was solved by the discovery of the fact that small rings of DNA other than the main DNA strands exist in the cells of bacteria. These circular DNA molecules are called plasmids. A technique was developed to insert foreign DNA fragments into plasmids taken out of the cells. This is known as gene splicing and plasmid becomes a vehicle or a vector.
Once the foreign DNA is joined to the plasmids, md inserted back in the host cell, the restriction enzymes fail to destroy it. When the cell reproduces, the foreign DNA .is also replicated. When the cell carries on its normal functions, the synthetic DNA in the plasmid directs the manufacture of the protein coded in i~. Thus, through genetic engineering tethniques, it is possible to introduce a foreign DNA into a host cell and synthesise any desired protein. Large quantities of scarce biologically significant proteins which are not easily available from natural sources can be manufactured in'this manner. For example, insulin needed by diabetic patients can now be produced on a large scale using this technique. Just as cattle are bred for specific functions like high milk yield, or pulling heavy loads, now-a-days scientists breed bacteria for carrying out special functions. By selecting suitable bacteria, and using genetic engineering techniques, new variel of bacteria which can eat man-made artificial products like plastics are being developed. Otherwise plastic materials, discarded and thrown in garbage, are hard to get rid off. These special bacteria are affectionately called 'Bugs'.