Which technique allows you to purify proteins based on size?

Size exclusion chromatography is the technique that allows for the purification of proteins based on their size. In this method, a column is filled with porous beads that allow smaller molecules to enter the pores while larger molecules are excluded and therefore pass through the column more quickly. As a result, proteins and other substances are separated based on their molecular size as they travel through the column.

The principle behind size exclusion chromatography relies on the notion that different sized molecules will elute from the column at different times, allowing for their separation. Larger proteins cannot enter the pores of the beads and traverse the column more rapidly, while smaller proteins get temporarily trapped in the beads, leading to a longer retention time.

This approach is particularly useful for separating biopolymers such as proteins, nucleic acids, and polysaccharides, making it a critical technique in biochemistry and molecular biology for protein purification, analyzing molecular weight, and assessing homogeneity of protein samples.

Other techniques like ion exchange chromatography focus on separating proteins based on charge, affinity chromatography is based on specific interactions between a protein and a ligand, and reverse phase chromatography separates compounds based on their hydrophobicity. Each of these methods serves different purposes and is chosen based on the specific separation needs of the experiment.