In which direction does DNA move during agarose gel electrophoresis, and why?

• A. Toward the positive electrode (anode) because DNA has a net negative charge due to its phosphate backbone.
• B. It moves randomly through the gel because the electric field affects only the loading dye, not DNA.
• C. It remains stationary in the wells because DNA is electrically neutral at the pH used for electrophoresis.
• D. Toward the negative electrode (cathode) because DNA has a net positive charge due to its phosphate backbone.

Answer: (A)

Verified step by step guidance

1. Understand that DNA molecules have a backbone made of phosphate groups, which carry a negative charge under physiological pH conditions.
2. Recall that during agarose gel electrophoresis, an electric field is applied across the gel with a positive electrode (anode) at one end and a negative electrode (cathode) at the other.
3. Since opposite charges attract, negatively charged DNA molecules will be pulled toward the positive electrode (anode) when the electric field is applied.
4. Recognize that the movement of DNA through the gel is influenced by the size of the DNA fragments, but the direction is always toward the anode due to the negative charge of the phosphate backbone.
5. Conclude that DNA does not move randomly or remain stationary because it is not electrically neutral; its net negative charge ensures directional movement toward the positive electrode.