Question

Centrifugation technique which uses CsCl for the separation of DNA is known as

• A. Differential centrifugation
• B. Ultra centrifugation
• C. High speed centrifugation
• D. Isopycnic centrifugation

Hint:

CsCl density gradient centrifugation is synonymous with isopycnic (equal-density) banding.
This historic method was used by Meselson and Stahl to prove the semi-conservative replication of DNA.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Centrifugation separates cellular components and biomolecules based on size, shape, and density.
Density gradient methods are used for high-resolution purification.

Step 2: Detailed Explanation:
- Isopycnic (equilibrium density gradient) centrifugation (D): Uses a self-generating gradient of a dense salt solution, typically cesium chloride (CsCl). During high-speed centrifugation, the CsCl redistributes to form a continuous density gradient. Biomolecules (like DNA) migrate through the gradient until they reach a position where their buoyant density matches the density of the surrounding solution (\(\rho_{\text{sample}} = \rho_{\text{gradient}}\)), where they form a stable band.
- Differential centrifugation (A): Separates particles primarily based on size and sedimentation rate using sequential increase in centrifugal force.
- Ultra centrifugation (B) and High-speed centrifugation (C): General terms referring to the speed of the centrifuge rotor rather than the specific biochemical separation mechanism.

Step 3: Final Answer:
The separation technique utilizing CsCl is Isopycnic centrifugation, corresponding to option (D).