When scientists began studying the way that bacterial cells protect themselves from different types of viral agents from bacteriophages, they realized that inside bacterial cells are these special digestive proteins, these special digestive enzymes known as restriction enzymes or restriction endonucleases. And what these restriction enzymes do is they are able to actually cut or cleave the viral DNA molecule into many different pieces, thereby destroying that viral DNA and deactivating that viral DNA. So one way that bacterial cells protect themselves from bacteriophages is by using these special enzymes we call restriction enzymes. Now, because there are many different possibilities that a DNA sequence can consist of, we have many, many different types of restriction enzymes that exist in nature. And each and every one of these restriction enzymes basically cleaves along a DNA molecule at a specific location on that double stranded DNA molecule. Now, many of these enzymes, in our study of these restriction enzymes, we realized that many of these restriction enzymes actually cut at palindromic sequences along that doublestrand the DNA molecule.