Q.42 Which of the following technique(s) can be used to separate proteins according to
their molecular weights from a mixture of proteins?
(A) Ion exchange chromatography
(B) Size exclusion chromatography
(C) Sodium dodecylsulfate – polyacrylamide gel electrophoresis (SDS–PAGE)
(D) Sucrose density gradient centrifugation

Size exclusion chromatography, SDS-PAGE, and sucrose density gradient centrifugation effectively separate proteins based on molecular weight or size from mixtures. Ion exchange chromatography does not, as it relies on charge differences. These methods are crucial for biochemistry and CSIR NET Life Sciences preparation.​

Question Analysis

The query asks which techniques separate proteins from a mixture according to molecular weights. Options include ion exchange chromatography (A), size exclusion chromatography (B), SDS-PAGE (C), and sucrose density gradient centrifugation (D). Correct answers are B, C, and D, as they rely on size-based sieving or sedimentation rates proportional to molecular mass under denaturing or standardized conditions.​

Option Breakdown

(A) Ion Exchange Chromatography

This technique separates proteins by net charge interactions with oppositely charged resin beads in a column. Proteins bind based on pH-dependent charge and elute via salt gradients disrupting electrostatic bonds. It does not distinguish molecular weights, focusing instead on ionic properties.​

(B) Size Exclusion Chromatography

Proteins pass through a porous bead-packed column where larger molecules elute first, unable to enter pores, while smaller ones delay inside them. Separation occurs purely by hydrodynamic size, correlating with molecular weight for globular proteins.​

(C) SDS-PAGE

SDS denatures proteins into linear chains coated uniformly with negative charge, eliminating shape and native charge effects. An electric field drives migration through polyacrylamide gel; smaller proteins move faster due to less frictional resistance, enabling molecular weight estimation via standards.​

(D) Sucrose Density Gradient Centrifugation

In rate-zonal mode, proteins sediment through a sucrose gradient at rates depending on size, shape, and mass during ultracentrifugation. Larger proteins travel farther, separating by effective molecular size without reaching buoyant equilibrium.​

Comparison Table