In electrophoresis, what happens to proteins during SDS-PAGE?

In SDS-PAGE (Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis), proteins undergo denaturation due to the action of SDS, which is an anionic detergent. SDS binds to the proteins and unfolds them into linear structures, effectively disrupting their three-dimensional shapes. This denaturation process ensures that the proteins are separated based solely on their molecular weight during the electrophoresis. The uniform negative charge contributed by SDS allows proteins to migrate through the gel matrix in a manner that corresponds primarily to their size, as the larger proteins encounter more resistance and travel more slowly than smaller ones.

This denaturing step is crucial because it eliminates the influence of charge and conformation on protein migration, enabling a clear analysis of the protein's size when visualized after electrophoresis. Although proteins can be stained post-electrophoresis for visualization, that process happens after the actual separation, making the other options less relevant in the context of what occurs during SDS-PAGE itself.