Practice question

Native proteins exhibit variable net charge depending on relationship between buffer pH and isoelectric point, affecting electrophoretic direction. Sodium dodecyl sulfate is strong anionic detergent possessing sulfate headgroup with persistent negative charge that binds along unfolded polypeptide chain at high density, approximately one molecule per two residues. Excess negative charges overwhelm intrinsic acidic and basic side chains, conferring uniform anionic character to all protein-SDS complexes proportional to length. Resulting micelles migrate toward positively charged anode during electrophoresis regardless of native pI. Positive, neutral or zwitterionic states do not persist after SDS saturation, ensuring size-based separation.