Question

Separation of proteins on the basis of molecular size is achieved by:

• A. Chromatography on a carboxymethyl (CM) cellulose column.
• B. Iso-electric focusing.
• C. Gel filtration chromatography.
• D. Chromatography on a diethylaminoethyl (DEAE) cellulose column.

Hint:

Size exclusion through porous gel beads, large molecules elute first, is the basis of gel filtration chromatography.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks which technique among the four listed separates proteins purely on the basis of their molecular size, rather than their charge or isoelectric point.

Step 2: Key Concept:
Gel filtration chromatography, also called size exclusion or molecular sieve chromatography, uses a column packed with porous beads. Large protein molecules cannot enter the small pores of the beads, so they travel around them and come out of the column first. Small protein molecules enter the pores, take a longer, winding path, and come out later. Elution order therefore follows molecular size, largest first.

Step 3: Detailed Explanation:
Chromatography on a carboxymethyl (CM) cellulose column is a cation exchange method, it separates proteins based on their positive charge at a given pH, not their size.
Iso-electric focusing separates proteins by their isoelectric point, the pH at which a protein carries no net charge, again this depends on charge properties, not size.
Chromatography on a diethylaminoethyl (DEAE) cellulose column is an anion exchange method, it separates proteins based on their negative charge at a given pH, not their size.
Gel filtration chromatography is the only one of the four that separates strictly by molecular size, using the pore structure of the gel beads.

Step 4: Final Answer:
Separation of proteins by molecular size is done by gel filtration chromatography.