Write a brief note on restriction enzymes. Explain the mechanism of action of restriction enzymes.

Explanation

The restriction enzymes act as molecular scissors that cut the DNA segment at the specific sites. The discovery of two such enzymes was made in 1963, one of which one was identified later as restriction endonuclease. The first restriction endonuclease was Hind II, the function of which is to recognise the specific sequence of six base pairs and cut the segment at that location. The restriction enzyme belongs to a larger class named nucleases. The two types of such enzymes are endonuclease and exonucleases. The exonucleases play a role in removing the nucleotides from the ends of DNA. It also inspects the length of DNA sequence. The endonuclease makes a cut at specific positions of DNA fragment. Once the restriction endonuclease finds a specific location, that has a capacity to recognise the palindromic nucleotide sequence, the enzyme gets bind to DNA and makes a cut at specific points in sugar-phosphate backbone of each of the two strands of the double helix. After the cutting, the overhanging sticky portion plays its role. The sticky end allows joining of two counterparts of DNA strand with the help of another enzyme called DNA ligase. The cuts made by restriction endonuclease give similar sticky ends at both the strands. After cutting, separation and getting attached to the host DNA, the recombinant DNA is formed.