Q.Write an essay on DNA recombinant technology.

Recombinant DNA technology cuts and joins DNA from different sources to create a recombinant molecule that a host cell is made to carry and express, enabling products from insulin to Bt cotton.

DNA recombinant technology, also called genetic engineering, is the deliberate manipulation of DNA to combine genetic material from different sources -- typically a gene of interest from one organism and a self-replicating carrier (vector) DNA molecule -- so that a host organism can be made to carry, replicate, and express a chosen gene.

Main steps of the process:

1. Isolation of the gene of interest: The DNA segment coding for the desired protein (for example, the human insulin gene) is identified and isolated from the source organism's genome, or synthesized/obtained through complementary DNA (cDNA) prepared from the corresponding mRNA using reverse transcriptase.

2. Cutting DNA with restriction endonucleases: Both the isolated gene and a suitable vector are treated with the same specific restriction enzyme (for example, EcoRI). These enzymes recognize specific short base sequences and cut the DNA at those points, commonly producing single-stranded, complementary sticky ends that can later base-pair with matching sticky ends on other DNA cut by the same enzyme.

3. Selection of a vector: A vector is a DNA molecule capable of independent replication inside a host cell and used to carry the foreign gene into that host. Common vectors include bacterial plasmids (such as pBR322), bacteriophages, and cosmids. The vector is cut open with the same restriction enzyme used on the gene of interest, so its ends are complementary to the gene's ends.

4. Ligation to form recombinant DNA: The cut gene of interest and the cut vector are mixed together, allowing their complementary sticky ends to base-pair, and the enzyme DNA ligase is used to seal the sugar-phosphate backbone at the joins, producing a single continuous recombinant DNA molecule (the gene now inserted into the vector).

5. Transformation (introducing recombinant DNA into a host cell): The recombinant DNA (vector plus insert) is introduced into a suitable host cell, most commonly the bacterium Escherichia coli, by making the host cells competent to take up DNA (for example, by brief treatment with calcium chloride and a heat shock) or by other methods such as electroporation.

6. Selection of transformants: Since not every host cell takes up the recombinant DNA, vectors are designed with selectable marker genes, typically genes conferring resistance to a specific antibiotic, or systems such as blue-white colony screening. Growing the host cells on a selective medium (e.g., containing that antibiotic) allows only successfully transformed cells to survive and be identified.

7. Multiplication and expression: The selected, transformed host cells are cultured (often at large industrial scale in bioreactors); as they multiply, they replicate the recombinant DNA and express the inserted gene, producing the desired protein, which is subsequently extracted, purified, and formulated for use.

Applications of recombinant DNA technology:

1. Production of human insulin (Humulin) by recombinant E. coli, replacing insulin earlier extracted from animal (pig/cattle) pancreas, for treating diabetes mellitus. …