Pouring a gel | Electrophoresis: How scientists observe fragments of DNA

Pouring an electrophoresis gel is the final step in preparing the molecular race track. The mold the gel is poured into is a plexiglass tray that is missing the two ends.

Quiz

Question

Why are the ends of the plexiglass tray missing?

so the liquid agarose runs out of both ends

Incorrect: current must flow through the gel so the ends must be open once the gel is solidified and in the gel box.

so a current can flow through the solidified gel

Correct: current must flow through the gel so the ends must be open once the gel is solidified and in the gel box.

to save money on equipment

Incorrect: current must flow through the gel so the ends must be open once the gel is solidified and in the gel box.

Looks Good! Correct: current must flow through the gel so the ends must be open once the gel is solidified and in the gel box.

Tape or removable ends are added prior to pouring to hold the hot liquid in place (Fig 5). A plexiglass comb is also added (Fig. 6). The teeth on this comb will stick into the cooling gel but not extend to the bottom of the mold. As the gel cools, each tooth in the comb forms a well. This is where the DNA sample will be placed. If many samples need to be compared in our electrophoresis race, combs with more teeth are used or more rows of combs are placed in the gel. When the gel cools, it solidifies to a semi-solid matrix that holds it’s shape. The comb can be removed from the solid gel and the empty wells will serve as the starting line for the DNA samples (Fig. 7). The tape is removed so current will flow through the gel once it is in the gel box (Fig. 8).