Practice question

Total size of a circular plasmid is sum of all fragments produced by complete restriction digestion, visualized by agarose electrophoresis. Observing two bands of 1200 bp and 3800 bp gives total 5000 bp, indicating full digestion into two fragments without loss. In circular DNA, number of fragments equals number of recognition sites cut, assuming enzyme cuts to completion. One site would linearize plasmid into single 5000 bp band. Two distinct bands therefore imply two HindIII sites spaced 1200 bp apart on one arc and 3800 bp on the other arc, confirming presence of second site for mapping.