Running an uncut DNA on electrophoresis is significant for 3 main reasons: 

1. Confirms plasmid purity– An uncut plasmid will run as a single band on the gel, which indicates that no contaminants are present in the plasmid preparation.
2. Helps assess plasmid quantity– The plasmid concentration in the preparation can be estimated based on the intensity of the uncut plasmid band. This is especially important for downstream applications such as transformation or transfection.
3. Acts as a quality control measure– Running an uncut plasmid on the gel is a vital quality control step that ensures the plasmid preparation is suitable for downstream applications.