Standard agarose gel electrophoresis for DNA size separation: gel preparation, sample loading with ladder, running, and visualization under UV/blue light.
Difficulty
beginner
Total time
1-2 hours
Biosafety
BSL-1
Steps
1
Place the agarose gel into the gel chamber
Carefully transfer the solidified agarose gel into the electrophoresis chamber, with the wells positioned closer to the negative (black) electrode.
▶ 00:45
2
Add electrophoresis running buffer
Fill the buffer reservoirs at both ends of the chamber with 1x running buffer (TAE or TBE) until the gel is fully submerged.
▶ 00:56
3
Load the samples
Pipette each DNA sample (already mixed with loading dye) into a separate well of the gel; include a DNA size ladder in the first or last lane.
▶ 01:49
4
Lower the pipette tip into the well
Gently lower the pipette tip just into the opening of the well without piercing the gel bottom; slowly dispense the sample.
▶ 01:56
5
Place the lid with correct polarity
Close the gel chamber lid ensuring the red (positive) and black (negative) terminals align correctly — DNA migrates toward the positive electrode.
▶ 02:29
6
Connect electrodes to power supply
Plug the red and black leads into the matching ports on the power supply.
▶ 02:42
7
Set the constant voltage
Set the constant voltage appropriate for the gel size — typically 80-120V (5 V/cm of gel length); too high can cause band smearing and overheating.
▶ 03:00
8
Set the timer and start the run
Start the timer for 30-60 minutes depending on band resolution needed; monitor the dye front, stop when it reaches about 2/3 of the gel length.
▶ 03:10
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