Practice question

Sodium dodecyl sulfate denatures proteins and coats unfolded chains with uniform negative charge essential for size-based separation. Quantitative binding studies demonstrate approximately 1.4 grams SDS bound per gram of protein, corresponding to one SDS molecule per two amino acid residues. This constant charge-to-mass ratio cancels intrinsic charge contributions, ensuring migration proportional to chain length. Ratios such as one-to-one, two-to-one, or 1.4-to-one per amino acid misrepresent established stoichiometry. Understanding this binding ratio explains why SDS-PAGE separates primarily by molecular weight regardless of native acidity or basicity and composition.