Which of the following statements about SDS PAGE is correct ?

a) Wanted proteins can be tested for their biological activity after separation by SDS PAGE
(b) Proteins are solubilised but not denatured when separated by SDS PAGE
(c) It separates protein on the basis of charge
(d) It separates protein on the basis of size

✅ Correct answer: (D) It separates protein on the basis of size

Explanation:

SDS-PAGE (Sodium Dodecyl Sulfate – Polyacrylamide Gel Electrophoresis) is a widely used technique to separate proteins based on their molecular weight (size).

• SDS (Sodium Dodecyl Sulfate) is an anionic detergent that denatures proteins and coats them with a uniform negative charge.
• This removes charge-based differences, ensuring that proteins migrate through the gel only based on their size (molecular weight).
• Smaller proteins move faster and travel farther in the gel, while larger proteins move slower.

Why Not the Other Options?

• (A) Wanted proteins can be tested for their biological activity after separation by SDS-PAGE ❌

  • Incorrect because SDS denatures proteins, meaning they lose their biological activity.
  • For functional activity, native PAGE is used instead of SDS-PAGE.

• (B) Proteins are solubilized but not denatured when separated by SDS-PAGE ❌

  • Incorrect because SDS completely denatures proteins by unfolding their structure.

• (C) It separates protein on the basis of charge ❌

  • Incorrect because SDS gives all proteins a uniform negative charge, eliminating charge-based separation.
  • IEF (Isoelectric Focusing) separates proteins based on charge, not SDS-PAGE.

Final Answer:

✅ (D) It separates protein on the basis of size