Question

A mixture of proteins (A, B, C and D) is separated on a Sephadex G-200 column. The proteins elute in the order of A, B, C and D. Assuming that all proteins are globular and monomeric, the protein with minimum electrophoretic mobility on SDS-PAGE will be

• A. A
• B. B
• C. C
• D. D

Hint:

In gel filtration, larger proteins elute first. In SDS-PAGE, larger proteins migrate slower. So, the first to elute in gel filtration has the least mobility in SDS-PAGE.

Answer 1

The Correct Option is A

Step 1: Understand gel filtration (Sephadex G-200) principle.
Gel filtration chromatography separates proteins based on size — larger molecules elute first as they bypass the pores, while smaller molecules enter the pores and elute later. Given elution order: 
A (first) → largest protein
D (last) → smallest protein 
Step 2: Understand SDS-PAGE principle. 
SDS-PAGE separates proteins based on molecular weight in a denatured state. SDS imparts a uniform negative charge, so proteins move according to size — smaller proteins migrate faster, and larger proteins move slower (i.e., have minimum electrophoretic mobility). 
Step 3: Analyze both techniques. 
Since protein A elutes first in Sephadex G-200, it is the largest. Hence, in SDS-PAGE, it will move the least (minimum mobility).