Genetic engineering is the manipulation and transfer of genes from one organism to another organisms to create a new DNA called as recombinant DNA (rDNA). The term recombinant is used because DNA from two different sources can be joined together. Hence, genetic engineering is also called as recombinant DNA technology.
Plasmid is the small circular double stranded DNA molecule found in the cytoplasm of bacterial cell and separated from chromosomal DNA. It can replicate independently.
Restriction enzymes recognises a specific base pair sequence (palindromic sequence) in DNA called as restriction site and cleaves the phosphodiester bond within DNA.
Techniques of Genetic Engineering – Basic Requirements
Important discoveries that led to the stepping stone of rDNA technology were:
- Presence of plasmid in bacteria that can undergo replication independently along with chromosomal DNA.
- Restriction enzymes cuts or break DNA at specific sites and are also called as molecular scissors.
- DNA ligases are the enzymes which help in ligating (joining) the broken DNA fragments.
What reminds to your mind when you hear the word clone? Of course, ‘DOLLY’ the cloned sheep. The carbon copy of an individual is often called a clone. However, more appropriately, a clone means to make a genetically exact copy of an organism. In gene cloning, a gene or a piece of DNA fragment is inserted into a bacterial cell where DNA will be multiplied (copied) as the cell divides.
A brief outline of the basic steps involved in gene cloning are:
- Isolation of desired DNA fragment by using restriction enzymes
- Insertion of the DNA fragment into a suitable vector (Plasmid) to make rDNA
- Transfer of rDNA into bacterial host cell (Transformation)
- Selection and multiplication of recombinant host cell to get a clone
- Expression of cloned gene in host cell.
Using this strategy several enzymes, hormones and vaccines can be produced
Development of Dolly
- Dolly was the first cloned female sheep, developed by Ian Wilmut and his colleagues at the Roslin Institute, Scotland in July 1996.
- She was created by somatic cell nuclear transfer technique.
- She lived for 6.5 years and died in 2003 because of lung disease.
Bio – Technology in Medicine
Using Genetic Engineering techniques medicinally important valuable proteins or polypeptides that form the potential pharmaceutical products for treatment of various diseases have been developed on a commercial scale.
Pharmaceutical products developed by rDNA technique:
- Insulin used in the treatment of diabetes.
- Human growth hormone used for treating children with growth deficiencies.
- Blood clotting factors are developed to treat haemophilia.
- Tissue plasminogen activator is used to dissolve blood clots and prevent heart attack.
- Development of vaccines against various diseases like Hepatitis B and rabies.
Gene therapy refers to the replacement of defective gene by the direct transfer of functional genes into humans to treat genetic disease or disorder. The genetic makeup of the ‘patient’ cell is altered using recombinant DNA technology. It was first successfully implemented in 1990.
Somatic gene therapy is the replacement of defective gene in somatic cells.
Germ line gene therapy replacement of defective gene in germ cell (egg and sperm).
Gene therapy conducted till date has targeted only somatic (non-reproductive) cells. Correction of genetic defects in somatic cells may be beneficial to the patient but the corrected gene may not be carried to the next generation.