The sorting out of molecules according to size and shape may be adapted to protein purification in this technique:

Ans. B. Gel filtration chromatographya. Size-exclusion chromatography, also called gel filtration, separates proteins according to size. The column matrix is a cross-linked polymer with pores of selected size. Larger proteins migrate faster than smaller ones, because they are too large to enter the pores in the beads and hence take a more direct route through the column.b. The smaller proteins enter the pores and are slowed by their more labyrinthine path through the column. Ion- exchange chromatography exploits differences in the sign and magnitude of the net electric charges of proteins at a given pH.c. The column matrix is a synthetic polymer containing bound charged groups; those with bound anionic groups are called cation exchangers, and those with bound cationic groups are called anion exchangers.d. Affinity chromatography separates proteins by their binding specificities. The proteins retained on the column are those that bind specifically to a ligand cross-linked to the beads. (In biochemistry, the term "ligand" is used to refer to a group or molecule that binds to a macromolecule such as a protein.)e. After proteins that do not bind to the ligand are washed through the column, the bound protein of particular interest is eluted (washed out of the column) by a solution containing free ligand.