How is it possible to sort different lengths of DNA strands using gel electrophoresis?

Question

aaronq · Answer

Yes it is. 

The gel matrix used (generally 10% agarose) creates tortuous (zig-zaggy) paths which the DNA strands have to navigate through. The gel is subjected to an electric field and due to the negative charges on the phosphate groups (on the backbone) the strands will travel from the negative end to the positive end. The advantage is that the amount of negative charge on the strands is the same regardless of length (a strand of 10 nucleotides will have 10 negative charges and one with 100 nucleotides will have 100 negative charges) so the electric force pulling them towards the positive end is the same.

Longer ones navigate slower (because they get trapped/tangled or experience friction) while slower ones travel faster.

jennithemeani · Answer

Uhm, can you like dumb that down? I still don't understan

anonymous · Answer

Yes, smaller strands move faster, larger ones move slower across the gel.

koikkara · Answer

i think, it is like... DNA electrophoresis is a method used to sort DNA molecules by length. Pieces of DNA are suspended in a tray of gel and subjected to an electric field, which causes them to migrate toward one end of the tray. The DNA separates out into bands, with the distance from the electrode corresponding to length of the strand. The technique plays a role in identifying genes for diagnosing disease and for other forms of genetic research. @jennithemeani