Q.4 Size exclusion chromatography or gel filtration chromatography separates proteins based on :
I. Stokes radii
2. Molecular weight and shape
3. Both 1 and 2
4. Colour

Size exclusion chromatography, also known as gel filtration chromatography, separates proteins based on their Stokes radii, which reflect both molecular weight and shape. This makes option 3 the correct answer, as it encompasses both factors listed.

Option Analysis

Stokes radii refers to the effective hydrodynamic radius of a protein in solution, determining how it navigates porous beads in the column. Larger Stokes radii elute first since they can’t enter pores, directly driving separation.

Molecular weight and shape influences Stokes radius—globular proteins of same weight but different shapes (e.g., elongated vs. compact) have varying hydrodynamic volumes, affecting elution order.

Both 1 and 2 is correct. Separation fundamentally relies on Stokes radius (option 1), which integrates molecular weight and shape (option 2); no interaction with the matrix occurs, purely size-based sieving.

Colour is irrelevant; this technique is non-interactive and doesn’t rely on optical properties like absorbance or pigmentation.​

Size exclusion chromatography separates proteins based on Stokes radii, sieving them through porous beads where larger hydrodynamic sizes elute faster without binding.

Mechanism Overview

A column of agarose or dextran beads with defined pores is equilibrated with buffer. Proteins > pore size exit in void volume; smaller ones diffuse in, delaying elution proportionally to their Stokes radius (hydrodynamic volume).

Key Factors

Stokes radius depends on mass, shape (e.g., monomers vs. aggregates), and solvation. No charge or affinity matters—pure size fractionation, ideal for desalting or oligomer analysis.

Exam Relevance

For GATE Biotechnology, questions on how size exclusion chromatography separates proteins based on Stokes radii emphasize non-denaturing purification over affinity methods.​