What technique separates proteins by size?

The technique that separates proteins by size is SDS-PAGE, which stands for sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This method involves denaturing proteins using SDS, a detergent that imparts a negative charge to the proteins, allowing them to unfold and move through a polyacrylamide gel matrix when an electric current is applied. The gel acts as a molecular sieve, enabling smaller proteins to migrate more quickly through the pores while larger proteins encounter greater resistance, thereby separating proteins based on their size during the electrophoresis process.

Other techniques, while important in biochemical analyses, do not primarily focus on separating proteins based on size. For example, Western blotting is used to detect specific proteins after they have been separated by SDS-PAGE, thus relying on SDS-PAGE for the initial separation step. ELISA is a method for quantifying proteins or antigens using antibodies, while chromatography refers to a group of techniques used to separate mixtures but often does so based on multiple properties, including charge, hydrophobicity, and size, depending on the specific type of chromatography used. Therefore, SDS-PAGE is specifically designed for the size-based separation of proteins.