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Gel electrophoresis is a powerful technique used to manipulate DNA and as an analytical tool, such as in DNA fingerprinting. Build your own gel electrophoresis device from scratch with simple materials, and use electricity to separate colored dyes.
For the electrophoresis chamber:
For the gel and buffer:
For the samples:
Make the comb:
Prepare your gel:
Set the electrodes in place:
Set up your power source and prepare your samples:
Once you have set up your gel, pour in just enough sodium bicarbonate buffer to cover the solidified gel. Make sure you fill up the spaces left from where you cut away the gel—the gel and stainless steel wires should be completely submerged.
Gently remove the comb by pulling straight up without tearing the gel. The wells left by the comb should fill with buffer.
Use the needle-tip pipette to transfer approximately 10 microliters (µL) of each sample to an empty well. (The volume of the thin tip of the pipette is about 10 µL.) Submerge the tip in the buffer directly above the well and gently squeeze the sample into the well. It should fall into the well since it is denser than the surrounding buffer. Be sure to use a new pipette for each sample to prevent contamination between samples. If you have a limited supply of pipettes, thoroughly rinse out the tip in a large beaker of water before reusing.
Once all the samples are loaded, connect the leads from the power supply to the stainless-steel wire electrodes attached to the box. Connect the negative terminal to the electrode at the top of the gel (near the wells) and the positive terminal to the electrode at the bottom of the gel. You should see bubbles forming along the electrodes when a complete circuit is made.
Leave the power connected for 15–20 minutes and observe what happens to each sample.
Gel electrophoresis is one of the most important tools used in molecular biology and genetic engineering. By conducting an electric current through an electrolyte buffer—like the sodium bicarbonate buffer that you used—charged molecules will migrate towards the terminal with the opposite charge. When suspended within a polymer matrix—such as an agar-agar gel—the molecules will move at different rates based on their size.
In this experiment, negatively charged dye molecules are loaded into the gel. When a current is passed through the gel, the molecules migrate towards the positive terminal, with smaller molecules moving faster than larger ones. This separates the different color molecules.
Look at the ingredient list of the food coloring you used to see what molecules are inside. Different brands can use different dyes. In the pictures shown here, we used Smart & Final brand dyes, which contain Blue #1, Red #40, and Yellow #5. Using gel electrophoresis, we discovered that McCormick-brand blue food coloring is made of a blue dye plus a small amount of red. McCormick red dye is actually made of two different red-colored molecules. Test different brands to discover the true composition of each color.
In molecular biology, this technique is used to separate biological compounds, such as DNA or proteins, based on their size. Like the colored dyes, DNA and proteins are negatively charged, so they will migrate towards the positive electrode at different speeds depending on their size.
Scientists can use special enzymes to cut a large strand of DNA into many smaller pieces. The size of the pieces will depend on the specific base sequence of the large DNA strand. This technique is used in DNA fingerprinting to identify people since each individual’s gene sequence will result in a unique “fingerprint” of DNA bands.
You can recycle the pieces of gel that you cut out before adding your samples. Simply reheat them in the microwave, and they will turn back into liquid.
Construct a protein through cereal additions.
Boundaries are the gift that keeps on sifting.
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Attribution: Exploratorium Teacher Institute