Which chemical provides anionic charge to proteins in SDS-PAGE?
Sodium dodecyl sulfate is an anionic detergent that binds cooperatively along the polypeptide backbone at approximately one molecule per two amino acid residues, corresponding to about 1.4 grams SDS per gram protein. This extensive binding imparts a large uniform negative charge that overwhelms intrinsic acidic and basic residues, disrupts non-covalent interactions, and unfolds proteins into rod-like micelles. Electrophoretic mobility then becomes proportional to chain length rather than native charge. Glycerol adds sample density, bromophenol blue tracks the front, and TEMED catalyzes polymer
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.