40.
In which of the following separation method where proteins are separated on the basis of their net charge

• (A) Affinity chromatography
• (B) Ion exchange chromatography
• (C) Dialysis
• (D) Gel filtration chromatography

  Answer: (B) Ion exchange chromatography

  Ion exchange chromatography separates proteins based on their net charge by exploiting differences in their surface charge at a specific pH.

  Option Analysis

  (A) Affinity Chromatography

  Affinity chromatography separates proteins based on specific biological interactions, such as binding between an enzyme and its substrate or antibody-antigen recognition.
  It uses a ligand attached to the matrix that selectively captures the target protein, not relying on net charge.

  (B) Ion Exchange Chromatography

  This method uses a charged resin (cation or anion exchanger) where proteins bind according to their net charge—positively charged proteins to negatively charged resins (cation exchange) and vice versa.
  Proteins are eluted by changing pH or salt concentration, allowing separation based on charge differences even for similar-sized proteins.

  (C) Dialysis

  Dialysis separates molecules by size using a semi-permeable membrane that retains larger proteins while small solutes like salts diffuse out.
  It does not involve charge-based separation; it’s purely diffusive based on molecular weight cutoff.

  (D) Gel Filtration Chromatography

  Also called size-exclusion chromatography, it separates proteins by hydrodynamic volume or size as larger molecules elute first from porous beads.
  Charge plays no role; separation depends on how proteins navigate the gel matrix pores.

  Proteins are key biomolecules in life sciences, and separating them by net charge using ion exchange chromatography is essential for purification in research and industry. This technique leverages protein charge differences at specific pH levels, making it a cornerstone for biochemistry students preparing for GATE Life Sciences exams.

  How Ion Exchange Chromatography Works for Net Charge Separation

  In ion exchange chromatography, proteins interact with a charged stationary phase: cation exchangers (negative resin) bind positive proteins, while anion exchangers (positive resin) bind negative ones.
  Elution occurs via salt gradients or pH shifts, where proteins with weaker charges elute first, enabling high-resolution separation.
  It’s ideal for proteins with similar sizes but different net charges, unlike other methods.

  Comparing Protein Separation Methods

  Method	Basis of Separation	Key Feature
  Affinity Chromatography	Specific binding (e.g., ligand-protein)	Highly selective, not charge-based
  Ion Exchange Chromatography	Net surface charge	Charge-dependent elution with salts/pH
  Dialysis	Size via membrane pores	Removes small molecules, no charge role
  Gel Filtration	Molecular size/volume	Larger proteins elute faster

  This table highlights why ion exchange is the go-to for net charge-based protein separation in competitive exams like GATE.

  Applications in Protein Purification

  Widely used in biopharma for monoclonal antibodies and enzymes, it scales from lab to industry.
  For GATE aspirants, understanding these distinctions aids in solving MCQs on biochemistry techniques.