6 When separating DNA using electrophoresis why does DNA sta

6. When separating DNA using electrophoresis, why does DNA start closest to the negative pole? (10 points)

Solution

The DNA is negatively charged naturally due to presence of phosphate groups in the nucleotide structure. Since opposite charges attract, the basis of agarose gel electrophoresis is based upon movement of DNA or RNA on agarose gel in a buffer across the potential gradient. Since the DNA/RNA are negatively charged by nature, they move towards the positive electrode or the anode.

However, loading of the test sample occurs near the negative pole or cathode since closer the DNA would be to the negative pole, more will be the repulsion between similar charges of cathode and DNA. This will provide the necessary repulsive force to the DNA for its movement across the agarose gel from the negative electrode or cathode towards the positive electrode or anode.

Thus, movement of DNA starts close from the cathode and traverses towards the anode.