What is the primary purpose of SDS in SDS PAGE electrophoresis?

The primary purpose of SDS (sodium dodecyl sulfate) in SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) is to denature proteins and impart a negative charge to them. SDS is an anionic detergent that disrupts the non-covalent interactions within proteins, leading to their linearization. This denaturation allows for the separation of proteins based solely on their molecular weight during electrophoresis.

In the process, because the SDS binds to the proteins and gives them a negative charge proportional to their length, this enables the proteins to migrate toward the positive electrode when an electric field is applied. Consequently, during electrophoresis, the proteins will separate according to size: smaller proteins move faster through the gel while larger ones move more slowly. This characteristic makes SDS-PAGE a powerful technique for analyzing protein samples based on size, as the denaturation process ensures that the proteins are uniformly negatively charged.

Considering the other options, maintaining pH levels is typically managed by buffers in the gel, separating nucleic acids is not the focus of SDS-PAGE since it targets proteins, and the addition of color to protein bands is usually done post-electrophoresis through staining methods, not through SDS