Final answer:
Proteins are separated in SDS-PAGE based on size, as SDS denatures the proteins and imparts uniform negative charges, allowing them to be sorted by molecular weight when an electric current is applied.
Step-by-step explanation:
SDS-PAGE and Protein Separation
Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) is a common laboratory technique used to separate proteins primarily based on size. During this process, the surfactant SDS is employed to denature proteins and confer upon them a uniformly negative charge by binding to their polypeptide chains. This effectively masks the protein's native charge variations that could affect migration during electrophoresis. As a result, when an electrical current is applied across the gel, the negatively charged proteins migrate towards the anode, with smaller proteins moving faster than larger ones because they encounter less resistance from the gel matrix. Thus, the key factor for the separation of proteins in SDS-PAGE is the molecular size, which enables the determination of the relative molecular mass of the proteins after staining and visualization.