Practice question

Under denaturing SDS-PAGE conditions, proteins saturated with SDS possess nearly identical charge-to-mass ratios because anionic detergent binding overwhelms native ionization of acidic and basic residues. Consequently, intrinsic charge, isoelectric point and solubility differences become negligible for electrophoretic velocity. Separation matrix then functions as molecular sieve where larger polypeptide-SDS complexes experience greater frictional retardation and migrate slower than smaller ones, making molecular size and chain length the dominant determinant of relative mobility. Parameters like charge and pI govern separation in native PAGE or isoelectric focusing, not under denaturing SDS conditions with uniform coating.