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Different sized pieces

When a restriction enzyme cuts up DNA, the number and size of the pieces you end up with depends on how often its cutting site turns up. For example, one (called Eco RI) cuts every time it finds the letters GAATTC, while another (called Alu I) cuts every time it finds AGCT. So scientists can choose different restriction enzymes, to cut up DNA into either lots of small pieces, or fewer larger pieces.

Restriction enzymes are precise scissors.

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