A. A cation-exchange matrix

B. A gel filtration matrix

C. An anion-exchange matrix

D. A plant cell wall constituent

Answer: (A) A cation-exchange matrix

Carboxymethyl cellulose (CM-cellulose) contains carboxymethyl (-CH₂COOH) groups that are negatively charged at neutral pH, making it a cation exchanger that binds positively charged proteins.[ from prior]

Option Analysis

(A) Cation-Exchange Matrix

Correct. CM-cellulose has negatively charged carboxyl groups (pKa ~4.5) that attract cations (positively charged proteins) at pH 6-8 when protein pI < buffer pH.​
Classic for hemoglobin purification; proteins elute with salt gradients.

(B) Gel Filtration Matrix

Wrong. Gel filtration (Sephadex, Bio-Gel) uses inert porous beads for size separation; CM-cellulose has charged functional groups, not size-exclusion properties.

(C) Anion-Exchange Matrix

Incorrect. Anion exchangers have positive charges (DEAE, Q-Sepharose) to bind anions (negative proteins); CM-cellulose is negatively charged.

(D) Plant Cell Wall Constituent

CMC is a derivative of cellulose (modified with carboxymethyl groups), not a natural plant cell wall component like native cellulose, hemicellulose, or pectin.

Carboxymethyl cellulose cation exchange matrix is widely used in biochemistry for separating positively charged proteins, essential knowledge for GATE Life Sciences aspirants.

Cation Exchange Mechanism

CM-cellulose beads have -OCH₂COONa groups; at working pH (6-8), these deprotonate to -COO⁻, creating negative charge that binds +ve proteins (pH < pI).​
Elution uses increasing NaCl (0.1-1M) or pH rise; weaker-binding proteins elute first. Introduced by Peterson & Sober (1956) for protein fractionation.​

Chromatography Matrix Comparison

This clarifies why carboxymethyl cellulose functions as cation-exchange matrix in exam contexts.

GATE Exam Applications

Frequently tested with ion exchange principles; remember CM = Carboxymethyl = Cation exchanger (negative matrix). Pairs with prior anion exchange questions.