Final answer:
In SDS-PAGE, all proteins are uniformly negatively charged due to SDS, leading them to migrate towards the positive electrode, and are separated based on molecular weight, as SDS masks charge differences.
Step-by-step explanation:
Proteins are separated on an SDS polyacrylamide gel based on size due to the action of Sodium Dodecyl Sulfate (SDS), a detergent that denatures proteins and imparts a strong negative charge, masking their native charge differences. In SDS-PAGE, the proteins all become uniformly negatively charged and thus are equally attracted to the positive electrode, anode, during electrophoresis. The separation of proteins occurs as the polyacrylamide gel matrix allows smaller proteins to migrate faster than larger ones, meaning that the migration speed is inversely proportional to the protein's molecular weight.
The effectiveness of SDS-PAGE lies in its ability to neutralize charge variability among proteins, ensuring that the separation during electrophoresis is based solely on molecular weight and not charge. Staining agents like Coomassie Blue or silver stain are used to visualize the separated proteins, with each band corresponding to proteins of different sizes. Thus, even proteins of the same size are attracted equally to the positive electrode due to the negative charges conferred by SDS.