They have the capacity to recognize specific base sequences on dna and then to cut each strand at a given place. The natural source of restriction endonucleases are bacterial cells. These enzymes are called restriction enzymes because they restrict infection of bacteria by certain viruses. Thus, their function in the bacterial cell is to destroy foreign dna that might enter the cell.
The restriction enzyme recognizes a particular sequence of base pairs about 4-8 bp long with an axis of rotational symmetry. The number and size of the fragments produced depends on the frequency of occurrence of the recognition site in the dna to be cut. Typically, 15-20 hydrogen bonds are formed between a dimeric restriction enzyme and the bases of recognition sequence. The restriction enzyme cuts the dna into smaller fragments so th. Ngomiv interact with two copies of their recognition sequence but cleave both sequences at the same time. Type ii restriction endonucleases recognize a palindromic sequence reads the same forward as backwards and make staggered cuts.
Once this site of recognition is established, it cleaves the phosphodiester bond in each strand of the double helical dna. Type ii restriction endonucleases recognize specific palindromic sequences a sequence that reads the same on both strands except one strand is reversed. The enzyme will cut the phosphodiester bond between g-a on both strands, resul. More than 3000 type ii restriction endonucleases have been discovered.