Practice question

SDS-PAGE combines denaturation with anionic detergent sodium dodecyl sulfate that confers uniform negative charge per unit length, nullifying intrinsic charge differences and unfolding proteins into rods. Migration through polyacrylamide sieving matrix becomes primarily size-dependent, with frictional resistance proportional to chain length. Smaller polypeptides encounter fewer obstacles, migrating farther and faster, while larger polypeptides experience greater retardation, remaining near top with slowest mobility. Tracking dye fronts indicate progress. This relationship allows molecular weight estimation using logarithmic calibration with standards, fundamental for assessing protein purity, subunit composition, and expression analysis.