restriction endonucleases are utilised in genetic engineering as molecular scalpels for cutting DNA at specific sites molecular builder of nucleotides molecular cement for combining DNA bits into long chains

Arestriction enzyme(orrestrictionendonuclease) is anenzymethat cutsDNAat or near specific recognitionnucleotide sequences known asrestriction sites.Restriction enzymes are commonly classified into three types, which differ in their structure and whether they cut their DNAsubstrateat 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 eachsugar-phosphate backbone(i.e. each strand) of the DNA double helix.