Polyacrylamide gel electrophoresis

Polyacrylamide gel electrophoresis (PAGE) is a technique used to analyze proteins by their size. It is quite similar to agarose gel electrophoresis that is used to analyze DNA after performing the PCR. However, before running a gel electrophoresis, our proteins are folded into complex 3D structures. Therefore, we must first denature the 3D structure of the proteins and make them linear. We can do this by adding sodium dodecyl sulfate (SDS), which is a detergent that unravels proteins to make them linear. SDS is also required to charge the proteins negatively. That is why this technique is commonly known as SDS-PAGE.

When the proteins are linearized and have a negative charge, we can load them onto a polyacrylamide gel and apply an electrical charge. The negatively charged proteins will travel through the porous polyacrylamide toward the positive pole, which is located at the end of the gel. The longer proteins will travel slower than the shorter proteins; this is how we can separate proteins by their length using polyacrylamide gel electrophoresis.

At the top of the image are SDS-coated proteins, visualised as black tangled strings of various sizes. Below, the proteins are put in blue rectangle with minus sign on top and plus sign at the bottom. The rectangular is called ‘Cross-linked polyacrylamide gel with electrical field applied’ and the arrow pointing down next to the rectangular shows the direction of migration. The last image at the bottom shows the same rectangle with the molecules of big size at the top, average size in the middle and small size at the bottom.

Figure 1. Polyacrylamide gel electrophoresis.