Tags: Enzyme.
A restriction enzyme (or restriction endonuclease) is an enzyme that cuts DNA at or near specific recognition nucleotide sequences known as restriction sites. Restriction enzymes are commonly classified into three types which differ in their structure and whether they cut their DNA substrate at their recognition site or if the recognition and cleavage sites are separate from one another. To cut DNA all restriction enzymes make two incisions once through each sugar-phosphate backbone (i.e.