Q34. A mixture of proteins (W, X, Y, Z) elute from Sephadex G-200 column in the order W, X, Y, Z.
The protein with maximum electrophoretic mobility on SDS-PAGE will be
Sephadex G-200 is a size-exclusion chromatography column where proteins elute from largest to smallest molecular weight, so W (first to elute) is the largest and Z (last) is the smallest. On SDS-PAGE, electrophoretic mobility inversely correlates with size—smaller proteins migrate fastest through the gel. Thus, Z has the maximum electrophoretic mobility.
Question Breakdown
Proteins W, X, Y, Z elute in that order from Sephadex G-200, meaning decreasing size: W > X > Y > Z. SDS-PAGE denatures proteins with SDS, giving uniform negative charge per mass, so separation depends solely on size; smaller polypeptides face less gel resistance and travel farther.
Option Analysis
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(A) W: Largest protein, elutes first, slowest on SDS-PAGE due to high mass.
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(B) X: Medium-large, elutes second, moderate mobility, not maximal.
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(C) Y: Medium-small, elutes third, good but not highest mobility.
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(D) Z: Smallest protein, elutes last, highest mobility as it sieves fastest.
Correct answer: (D) Z.
Proteins eluting from Sephadex G-200 in order W, X, Y, Z follow size-exclusion principles where largest proteins like W exit first. Sephadex G-200 elution order reveals native size hierarchy, vital for biochemistry and GATE Life Sciences prep.
Size-Exclusion Chromatography Basics
Sephadex G-200 uses porous beads; large proteins (W) are excluded and elute early, while small ones (Z) enter pores, delaying exit. This decreasing molecular weight order (W largest, Z smallest) sets up SDS-PAGE contrast.
SDS-PAGE Electrophoretic Mobility
In SDS-PAGE mobility, SDS denatures proteins to linear chains with charge proportional to length; smaller Z migrates farthest as it navigates polyacrylamide mesh quickest. Unlike native PAGE, native charge is nullified.
| Technique | Separation Basis | Order for W>X>Y>Z |
|---|---|---|
| Sephadex G-200 | Native size (MW) | W first, Z last |
| SDS-PAGE | Denatured size (smaller = faster) | Z first, W last |
GATE Exam Application
For competitive exams, link Sephadex G-200 elution order to inverse SDS-PAGE mobility: smallest Z wins max mobility. Practice with molecular weights (e.g., 150>50 kDa elutes large-first) reinforces concepts.
