A restriction enzyme – or restriction endonuclease – is a enzyme that facilitates the separation of DNA at specific nucleotide sequences. Each restriction enzyme recognizes a unique sequence of ~5 nucelotides and will ‘cut’ the DNA between two nucleotides. Sometimes these cuts will leave overlapping ends of DNA on each fragment which are called ‘sticky-ends’. Other enzymes leave cuts without these overhangs, called ‘blunt-ends’.
Restriction enzymes are naturally found in bacteria and protect bacteria from foreign bacteriophage DNA that try to infect them.
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