The restriction enzymes are called 'molecular scissors' and are responsible for cutting DNA on specific sites. These are not found in viruses. They are present in bacteria to provide a type of defense mechanism called the 'restriction modification system' and the so called system consist of two components; restriction enzymes and modification enzyme. The first component include restriction endonuclease, which identify the introduced foreign DNA and cut it into process. Same kind of sticky end in different individual molecule of DNA are also produced by these molecular scissors. Special sequence in the DNA recognized by restriction endonuclease is called palindromic nucleotide sequence.