A. The column contains negatively charged beads where positively charged proteins bind

B. The column contains positively charged beads where negatively charged proteins bind

C. The column contains both positive and negatively charged beads where proteins bind depending upon their net charge

D. All of these

Answer: (B)

In anion exchange chromatography, the column contains positively charged beads (like DEAE groups) that bind negatively charged proteins, which is the defining mechanism of this technique.

Option Analysis

(A) Negatively Charged Beads for Positive Proteins

This describes cation exchange chromatography, where negatively charged resins (e.g., carboxymethyl groups) attract positively charged proteins—not anion exchange.

(B) Positively Charged Beads for Negative Proteins

Correct for anion exchange. Proteins with net negative charge (pH > pI) bind to positive resins like diethylaminoethyl (DEAE); elution uses salt gradients where less negative proteins elute first.

(C) Both Positive and Negative Beads

No standard chromatography uses mixed-charge beads in a single column; this would cause non-specific binding and poor resolution. Separate cation/anion columns are used sequentially.​

(D) All of These

Incorrect, as only option B defines anion exchange specifically.​

Anion exchange chromatography uses positively charged beads to separate negatively charged proteins, a key technique in protein purification for biochemistry and GATE Life Sciences preparation.

Anion Exchange Column Mechanism

The stationary phase contains positively charged functional groups (e.g., DEAE, quaternary ammonium) that electrostatically attract proteins with net negative charge at the chosen pH (> protein pI).
Proteins bind with varying strength based on charge density; a salt gradient (NaCl) elutes them competitively, with weakly bound proteins first.
Common for purifying acidic proteins like antibodies or enzymes.​

Ion Exchange Chromatography Types Comparison

This table clarifies why positively charged beads define anion exchange for exam questions.​

GATE Exam Relevance

Critical for MCQs on chromatography principles; remember: anion = attracts anions (negative proteins).​