Which description correctly explains how SDS-PAGE causes proteins to separate primarily by size?

• A. SDS adds bulky neutral polymers to proteins which makes them excluded from the polyacrylamide pores and causes migration based on how well proteins bind to the gel surface rather than any sieving by size.
• B. SDS selectively digests proteins down to short peptides so that only the smallest fragments move through the gel and separation therefore solely reflects enzymatic digestion patterns rather than molecular size.
• C. SDS denatures proteins and coats them with a roughly uniform negative charge proportional to length, while polyacrylamide matrix sieves molecules so migration depends mainly on polypeptide length (size) not native charge differences.
• D. SDS crosslinks protein subunits into rigid complexes that then migrate through the gel based on the protein's original charge that SDS amplifies by adding multiple positive charges to basic residues.

Answer: (C)