Answer to Question #141728 in Molecular Biology for Bari

Question

What is the purpose of running an uncut sample of the plasmid (on electrophoresis gel) ?

Why should the PCR sample on the gel only have a single fragment?

Answer 1

The purpose of running an uncut sample of the plasmid on electrophoresis gel is to check the progression of a restriction enzyme digestion, to quickly determine the yield and purity of a DNA isolation or PCR reaction, and to size fractionate DNA molecules, which then could be purified from the gel if necessary.

The PCR sample on the gel should only have a single fragment since all DNA molecules have the same amount of charge per mass. Due to this, gel electrophoresis of DNA fragments separates them based on size only. Small fragments move through the gel faster than large ones.