GATE BT 2025 • Q23 MSQ • 1 Mark

Section 4: Bioprocess Engineering and Process Biotechnology

Downstream processing (chromatography, filtration)

Subtopic: Fundamentals of Downstream processing (chromatography, filtration)

Question Statement:

Which of the following separation processes is/are based on molecular size?

Options:

  • (A) Size-exclusion chromatography
  • (B) Ion exchange chromatography
  • (C) Membrane ultrafiltration
  • (D) Ultracentrifugation

Official Answer Key:

A;C;D

Step-by-Step Solution & Explanation

### **Official Solution & Concept Analysis (GATE BT 2025 Q.23)** **1. Governing Concept**: - **Topic**: Downstream Processing & Biophysical Separation Principles - Separation techniques exploit different physicochemical properties of biomolecules: - **Size / Hydrodynamic Volume**: Size-Exclusion Chromatography (Gel filtration), Ultrafiltration (MWCO membranes), Dialysis, SDS-PAGE (sieving mesh). - **Charge**: Ion-exchange chromatography, Isoelectric focusing. - **Hydrophobicity**: Hydrophobic interaction chromatography (HIC), Reverse-phase HPLC. - **Biological Affinity**: Immunoaffinity, metal chelate affinity (IMAC). **2. Option Analysis**: - **Option (A) [Gel filtration chromatography] is CORRECT**: Also called size-exclusion chromatography (SEC); porous stationary phase fractionates solutes strictly according to hydrodynamic radius/molecular size. - **Option (B) [Ion-exchange chromatography] is INCORRECT**: Separates molecules based on net surface charge density. - **Option (C) [Ultrafiltration] is CORRECT**: Pressure-driven membrane process with specific molecular weight cut-off (MWCO) rating that separates solutes by molecular size. - **Option (D) [Dialysis] is CORRECT**: Passive diffusion through a semi-permeable membrane with discrete pore sizes, separating small salts from large macromolecules based on size. **3. Final Answer**: - **Correct Options**: **A, C, D**

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