Difference Between Differential and Density Gradient Centrifugation

Main Difference – Differential vs Density Gradient Centrifugation

Centrifugation is a separation method in which the rotation of the sample around a fixed axis produces a centrifugal (g) force. The particles or cells in the sample are forced down through a liquid medium by the centrifugal force. The rate of sedimentation is determined by the density and the size of the particles or cells. As the sedimentation of particles or cells with different densities and sizes occur in different rates, they are physically separate from each other at some point of centrifugation. Differential centrifugation and density gradient centrifugation are the two main types of centrifugation. The main difference between differential and density gradient centrifugation is that fractionation is carried out based on the size in differential centrifugation whereas fractionation is carried out based on the density in density gradient centrifugation.

Key Areas Covered

1. What is Differential Centrifugation
     – Definition, Facts, Process
2. What is Density Gradient Centrifugation
    – Definition, Facts, Process
3. What are the Similarities Between Differential and Density Gradient Centrifugation
     – Outline of Common Features
4. What is the Difference Between Differential and Density Gradient Centrifugation
     – Comparison of Key Differences

Key Terms: Density, Density Gradient Centrifugation, Differential Centrifugation, Differential Pelleting, Equilibrium Centrifugation, Isopycnic Centrifugation, Rate-Zonal Centrifugation, Size

What is Differential Centrifugation

The differential centrifugation refers to the simplest form of the centrifugation. It is also known as differential pelleting. The components of a cell can be separated by differential centrifugation. The differential centrifugation is based on the size of the particles in the solution. Thus, the particles with different sizes sediment at different rates during the centrifugation. The larger particles sediment faster than the smaller particles. The sedimentation rate can be increased by increasing the centrifugal force. The differential centrifugation is shown in figure 1.

Figure 1: Differential Centrifugation

Ideally, the differential centrifugation is used to harvest cells or to produce crude subcellular fractions from a tissue homogenate. For example, a liver homogenate may contain nuclei, mitochondria, lysosomes, and membrane vesicles. When the liver homogenate is centrifuged at low speed for a short time, the large nuclei sediment in the pellet. When a higher centrifugal force is used mitochondria also sediment in the pellet. Due to the homogeneity of biological samples, the sedimentation always contaminates.

What is Density Gradient Centrifugation

Density gradient centrifugation refers to a separation method in which the substances are concentrated in the solutions of caesium salts or sucrose. It is involved in the fractionation of particles on the basis of buoyancy density. The caesium salts or sucrose solution is called the density gradient. The two types of density gradient centrifugation are rate-zonal centrifugation and isopycnic centrifugation. 

Rate-Zonal Centrifugation

During the rate-zonal centrifugation, the sample is layered as a narrow zone on top of a density gradient. Particles move at different rates under the centrifugal force on the basis of their density. The actual sedimentation rate primarily depends upon the size and mass of the particles. As the density of the particles is higher than the density gradient, all particles produce pellets. Density gradient centrifugation is shown in figure 2.

Figure 2: Density Gradient Centrifugation

Isopycnic Centrifugation

Isopycnic centrifugation starts with a homogeneous solution. Under centrifugal force, the particles move until their density is similar to the density gradient. Thus, the isopycnic centrifugation is also known as buoyant or equilibrium centrifugation. Biological particles depend on the osmotic pressure of the density gradient. Therefore, the gradient medium should contain a similar osmotic pressure as the cells or organelles.

Similarities Between Differential and Density Gradient Centrifugation

• Differential and density gradient centrifugation are two types of centrifugation methods.
• Both differential and density gradient centrifugation are involved in the separation of particles or cells based on their physical properties.

Difference Between Differential and Density Gradient Centrifugation

Definition

Differential Centrifugation: Differential centrifugation refers to a separation method where the components of a cell are separated on the basis of their density in a centrifuge according to the centrifugal force they experience.

Density Gradient Centrifugation: Density gradient centrifugation refers to a separation method where the substances are concentrated in the solutions of cesium salts or sucrose.

Separation

Differential Centrifugation: The separation occurs based on the size of the particles in differential centrifugation.

Density Gradient Centrifugation: The separation occurs based on the density of the particles in density gradient centrifugation.

Types of Molecules

Differential Centrifugation: Differential centrifugation is used to separate cells, organelles or macromolecules.

Density Gradient Centrifugation: Density gradient centrifugation is used to separate molecules or particles.

Type of Sample

Differential Centrifugation: A homogenized organ is used as the sample in differential centrifugation.

Density Gradient Centrifugation: A homogenized solution is used as the sample in density gradient centrifugation.

Sugar Solution

Differential Centrifugation: No sugar solution is used in the differential centrifugation.

Density Gradient Centrifugation: A sucrose or any sugar solution is used in the density gradient centrifugation.

Easiness of the Method

Differential Centrifugation: Differential centrifugation is easy to use.

Density Gradient Centrifugation: Density gradient centrifugation is difficult to use.

Contamination

Differential Centrifugation: No contamination occurs in differential centrifugation.

Density Gradient Centrifugation: Some contamination is always possible in density gradient centrifugation.

Conclusion

Differential and density gradient centrifugation are two methods of centrifugation used to separate particles. Differential centrifugation separates particles based on their size. However, density gradient centrifugation separates particles. The main difference between differential and density gradient centrifugation is the type of physical property on which each type of centrifugation method is based on.

Reference:

Image Courtesy:

1. “Differentielle zentrifugation” By Thomasione – Own work (Original text: selbst erstellt) (Public Domain) via Commons Wikimedia
2. “Density gradient” By The original uploader was Mlw3559 at English Wikibooks – Transferred from en.wikibooks to Commons. (CC BY-SA 2.5) via Commons Wikimedia