Q. The enzymes which are absolutely necessary for recombinant DNA technology are
(a) restriction endonucleases and topoisomerases
(b) endonucleases and polymerases
(c) restriction endonucleases and ligases
(d) peptidases and ligases.
Answer (c) : An important step in the process of genetic engineering is the preparation of recombinant DNA (rDNA). For this, the vector DNA and foreign DNA (carrying gene of interest) are needed to be cut at specific sites and joined to produce rDNA. This is achieved by enzymes, restriction endonucleases and DNA ligases. Restriction endonucleases act as molecular scissors or chemical scalpels which recognize the base sequence at palindrome sites in DNA duplex (a section of dsDNA having sequence of bases on one strand inverted and repeated on the other) and cut each of the two strands of the double helix at specific points in their sugar phosphate backbones. DNA ligases are known as genetic gum as they form phosphodiester bonds between adjacent nucleotides and covalently link two individual fragments of dsDNA.
