In electrophoresis, which of the following is correct about electrode placement?

• A. The negative electrode (Black) should be nearest to the wells
• B. The electrodes can be connected in any order
• C. The wells should be submerged after running
• D. The buffer is not required

Answer: (A)

DNA fragments are negatively charged, so they migrate toward the positive electrode during gel electrophoresis. Placing the negative electrode near the wells creates the correct direction of movement, sending the fragments through the gel toward the opposite end where separation by size occurs. The buffer is essential because it conducts the current and helps maintain a stable pH throughout the run. Polarity matters: reversing the electrodes would push DNA in the opposite direction and ruin the separation. The gel must be submerged in buffer during the run for current to flow; running without buffer would stop the process.