Living organisms have numerous biochemical reactions operating in them. These reactions allow the organisms to survive by processes such as generation of energy, production of fundamental building blocks required for structural organization and synthesis of biomolecules having specialized functions. Some of the chemicals generated during this process (called metabolism), are useful to mankind for various applications.

 These so-called valueadded chemicals include various bioactive secondary metabolites such as an anti-malarial drug (artemesinin), chemicals required as the raw material for the synthesis of other molecules such as lactic acid, chemicals imparting flavor to food material such as terpenes, biofuels and associated chemicals such as ethanol and butanol, etc. The traditional way of utilization of such chemicals is to cultivate the host organisms producing these chemicals followed by harvesting the desired biochemical. However, in many cases, the quantities of the useful chemicals in the cells are very low, thus demanding cultivation of the organisms on a very large scale.

To address this problem, organic chemists have come up with brilliant ways to chemically synthesize such value-added chemicals from the petroleum crude material. However, this strategy has its own disadvantages. Rapidly depleting petroleum resources and production of racemic mixtures1 and harmful byproducts are some of the issues which are forcing scientists to find out the alternative ways to generate these value-added biochemicals. Sinceliving organisms already producethese chemicals, copying their biosynthesis mechanisms for their semi-natural production appears to be an excellent alternative to their isolation from natural resources and the chemical synthesis. Such an approach for the production of desired chemicals in living organisms is called metabolic engineering.