If Proteins in SDS-PAGE Possess the Same Charge-to-Mass Ratio, How Is Their Separation Achieved?
When we state that proteins in SDS-PAGE exhibit the same charge-to-mass ratio, it means that in the presence of SDS, proteins are denatured into linear polypeptide chains uniformly coated with negative charges. Specifically, approximately one SDS molecule associates with each amino acid residue, ensuring that the electrophoretic mobility of a protein in the electric field becomes inversely related to its molecular weight and is independent of its native charge.
Protein separation in SDS-PAGE is accomplished according to molecular size. Proteins with smaller molecular weights migrate through the polyacrylamide gel matrix more rapidly than those with larger molecular weights. This occurs because the gel’s pores offer less resistance to smaller proteins, allowing them to pass more easily, while larger proteins experience greater hindrance as they move through the gel network.
In summary, although all proteins acquire a nearly uniform charge-to-mass ratio, they are effectively separated within the polyacrylamide gel based on differences in their molecular size.
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