Practice question

SDS-PAGE migration primarily reflects polypeptide length due to uniform SDS charge coating, overwhelming intrinsic charge. Post-translational modifications that add neutral mass retard mobility without altering isoelectric point. N-linked and O-linked glycosylation attaches bulky hydrophilic carbohydrate chains lacking proportional SDS binding and charged groups, increasing hydrodynamic size and apparent molecular weight substantially while pI remains largely unchanged because glycans are mostly neutral. This produces slower, often smeared migration. Phosphorylation, ubiquitination and acetylation add or remove charges, influencing both pI and mobility, unlike neutral glycosylation which mainly increases mass.