醫學分子檢驗學與臨床鏡檢學（包括寄生蟲學題庫下載題庫

How many times can a restriction enzyme cut a piece of DNA?

The probability that a given enzyme will cut, or “digest”, a piece of DNA is directly proportional to the length of its recognition site.  Statistically, an enzyme will average one cut for every 4ⁿ base pairs, where n is the length of the recognition site.  Therefore, the longer a DNA molecule is, the greater the probability is that it contains one or more restriction sites.  For instance, an enzyme that recognizes six base pairs (e.g., EcoRI) will cut once every 4096 (or 4⁶) base pairs. If EcoRI is used to digest both human chromosomal DNA and a plasmid, it will cut the chromosomal DNA over 700,000 times (3 billion base pairs, cut every 4096 base pairs), but may only cut the plasmid once (5,000 base pairs, cut every 4096 base pairs).

https://blog.edvotek.com/2014/06/13/biotech-basics-restriction-enzymes/