Practice question

In electrophoresis, migration depends on charge to mass ratio and molecular sieving. DNA possesses a uniform negative charge due to phosphate backbone, one per nucleotide, resulting in nearly identical charge/mass ratio for all fragments. Consequently, in free solution, all DNA migrates equally. Separation in agarose or polyacrylamide occurs due to frictional resistance of the porous matrix, where longer molecules experience greater retardation. Thus, although labeled as size-based separation, the underlying principle involves differential mobility governed by charge/mass ratio interacting with sieving and frictional forces.