What is Genetic Engineering? Principle, Steps, Scope & Applications

Genetic engineering is an important principle of biotechnology through which the genetic material of an organism is either altered or modified to obtain desirable traits. The process is also called genetic modification. The main pillar of genetic engineering is recombinant DNA technology (RDT). With the development of genetically modified crops, the agricultural yield is increasing day by day.

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What is Genetic Engineering?

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The method through which the genetic makeup of a living organism is changed or modified in an artificial (laboratory) environment is called genetic engineering. Modification of genetic material can be done by either inserting or removing a desired gene or segment of DNA. The method of genetic engineering is showing successful and better results in the fields of medicine, research and agriculture.

• The word genetic engineering was first introduced by Jack Williamson in 1951 in his science fiction novel “Dragon’s island”.
• The first crop developed using genetic engineering technique was tobacco plant  in 1983. 

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Principles of Genetic Engineering

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The process of genetic modification works on the principle of recombinant DNA technology. The principle of genetic engineering is given as:

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Recombinant DNA Technology

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Recombinant DNA is simply the term used to refer to the altered DNA which consists of the desirable traits. The first case of the creation of an artificial recombinant DNA can be traced back to 1972 in the work of Stanley Cohen and Herbert Boyer, who separated the antibiotic resistance gene from a plasmid showing antibiotic resistance.

The DNA with the desirable trait was isolated by cutting it from its specific location using restriction enzymes also known as molecular scissors. The DNA thus isolated was linked to plasmid DNA which acts as a vector that will help transfer it to the host. The enzyme DNA ligase was used to link the DNA with antibiotic resistance to the vector.

The recombinant DNA thus produced was inserted into Escherichia coli, which was then able to multiply using the enzyme DNA polymerase of the host. The E.coli was thus given the ability to clone the antibiotic resistance gene. The technology used to create alternate genes with desirable traits (recombinant DNA) is called recombinant DNA technology.

Steps in Recombinant DNA Technology

There are six important steps involved in recombinant DNA technology which are discussed below: 

• Isolation of DNA: For the restriction enzyme to function the DNA needs to be free. This means that the DNA must be extracted from the cell which is done by treating the cells with enzymes such as lysozyme for bacteria, cellulase for plant cells and chitinase for fungi. 
• Cutting of DNA: The desirable DNA is cut using restriction endonucleases which acts when the optimal environment is maintained. Agarose Gel electrophoresis is employed to separate the DNA. This is repeated for the vector. Finally, the DNA with desirable traits is joined with the vector using ligase. 
• Amplifying the Gene of Interest: This is done using Polymerase Chain Reaction or PCR. The enzyme DNA polymerase is utilized to synthesise multiple copies of the DNA via 2 sets of primers. 
• Introducing recombinant DNA to the host:  This is done using a process called micro-injection, where the recombinant DNA is injected into the host cells. For plants, the gene-gun or biolistics is used where the cells are bombarded with microparticles of tungsten or gold that are coated with DNA at high velocity. 
• Producing desirable protein: The foreign gene that has been inserted into the host will express itself under suitable conditions. The protein that will be produced is called recombinant protein. When these proteins are to be produced in large amounts, bioreactors are necessary. 
• Downstream Processing: This stage includes separation and purification of the product. It is the last stage that is accompanied by quality testing. In the case of drugs, clinical trials are also involved. 

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Tools used for Recombinant DNA Technology

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Recombinant DNA technology or genetic engineering utilizes tools namely restriction enzymes, ligases, vectors, polymerase enzyme and the host. 

• Restriction Enzyme

Restriction endonucleases are enzymes that cut the DNA at particular sites known as recognition sequence. The restriction endonuclease studies the DNA strand to find the specific sequence. Once it identifies the location of the recognition sequence, the enzyme will bind to the double helix structure and cut both strands at specified locations. As the sequence identified by restriction endonucleases are palindromic in nature they are called palindromic nucleotide sequences.

• Ligase

After the restriction endonuclease cuts the DNA sequence, it leaves overhanging sticky ends, which are able to form hydrogen bonds with their complementary parts. The enzyme ligase act at these points to combine the two ends. 

Also, it is important to note that ligases can only join the ends cut by the same restriction endonuclease. This is because the sticky ends will be the same if the restriction enzyme used is the same. 

• Vector

Vectors are the strands of DNA that act as carriers for the desired DNA to be transferred into the host organism. 

• Host

The host is the organism to which the recombinant DNA is introduced. The goal is for the desired traits to be induced into the host.