Affinity vs. ion-exchange vs. size-exclusion chromatography
A His-tagged recombinant protein is purified on a nickel-coated column and eluted with imidazole. This technique is:
Answer D: explanation for every choice
A
Size-exclusion separates by size. Small molecules enter the bead pores and elute later.
B
Ion-exchange separates by net charge and elutes with a salt or pH gradient.
C
Thin-layer chromatography separates small molecules by polarity on a coated plate.
D
Correct. The histidine tag binds Ni²⁺ specifically, and imidazole, which resembles histidine's side chain, competes for binding and releases the protein.
TakeawayAffinity: a specific binding partner. Size-exclusion: large molecules elute first.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb18.