How do SDS-PAGE separate proteins?

SDS-PAGE, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis, separates proteins primarily based on their mass. In this technique, proteins are denatured and coated with SDS, an anionic detergent that imparts a negative charge to each protein. This uniform charge allows the proteins to migrate through a polyacrylamide gel matrix in an electric field.

As proteins move through the gel, they encounter resistance based on their size, with smaller proteins moving through the gel more easily and quickly than larger ones. Thus, the separation is effectively determined by the mass of the proteins. After electrophoresis, the proteins can be visualized, typically through staining methods, allowing for size determination by comparison to a molecular weight marker.

This method does not rely on charge, shape, or solubility for separation; instead, it specifically exploits size differences among proteins. Therefore, mass is the salient factor allowing for effective differentiation of proteins in SDS-PAGE.