Final answer:
A restriction endonuclease is an enzyme that cuts DNA at specific recognition sites, typically four to six base pairs in length that are palindromic sequences. They are essential for DNA manipulation in molecular biology and genetic engineering.
Step-by-step explanation:
A restriction endonuclease (restriction enzyme) is an enzyme that cuts DNA at specific recognition sites. These sites are unique sequences of nucleotides, frequently palindromic, meaning they read the same forward and backward on the two DNA strands. Restriction enzymes are instrumental in genetic engineering and diagnostics as they can create a DNA 'fingerprint' and are used to splice DNA fragments during cloning. For instance, the restriction enzyme EcoRI cuts DNA at the sequence 5'GAATTC 3', producing 'sticky ends' which can be used to join the cut DNA with another DNA strand.
These enzymes have a high level of specificity, targeting only specific DNA sequences and cleaving with high precision. They are a vital tool in molecular biology for cutting and studying DNA as well as for recombinant DNA technology, where DNA from different sources can be combined.