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Biology LibreTexts

8.4: Load and run the agarose gel

  • Page ID
    17541
    1. When the gel has set, carefully remove the comb and the black wedges.

    2. Orient the gel in the electrophoresis tank such that the wells (holes made by the comb) are oriented toward the black (negative) electrode. DNA molecules will move from the well toward the red (positive) electrode. Fill the tank with enough TAE buffer to submerge the gel (approx. 275-300 mL).

    3. Load one sample to each well, which can accommodate ~20 μL. Load 10-12 μL of a PCR sample to each lane. Try to avoid air bubbles as you load the samples.

    4. Load 5 μL molecular weight standard to one lane of the gel. Make sure that you have accurately recorded the location of each sample in the gel.

    5. Place the lid on the electrophoresis tank and connect the electrodes to the power supply (black-to-black and red-to-red). Make sure that the polarity is correct before continuing!

    6. Turn on the power and apply a constant voltage of 125 V.

    7. Pay careful attention to the gel as it runs. Turn off the power when the bromophenol blue is ~ 2 cm from the end of the gel. Do not allow the dye to run off the gel, since small DNA molecules will be lost. (Think about the size of your PCR products.)

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