In rate-zonal centrifugation, a mixture is spun just long enough to separate molecules that differ in mass but may be similar in shape and density. which one of the following options represents the component that is typically used to create a gradient in this technique?

Question( June 2024):  In rate-zonal centrifugation, a mixture is spun just long enough to separate molecules that differ in mass but may be similar in shape and density. which one of the following options represents the component that is typically used to create a gradient in this technique?

1. Phospholipids
2. Sucrose
3. K Cl
4. Starch

Answer: 2. Sucrose

 Mass of Phospholipid-740-757 Da

PC (Phosphatidylcholine)= 757 Da

PE ( Phosphatidylethanolamine)=715 Da

PS (Phosphatidylserine)= 758 Da

PI ( Phosphatidylinositol)=833 Da

Mass of Sucrose= 342.3 g/mol

Mass of  K cl=74.55 g/mol

Mass of starch=3.75 *108 g/mol

Rate zonal centrifugation method , materials used for preparation of density gradients are sucrose, glycerol, ficoll .

Explanation of facts:

 Centrifugation is a method employed to separate or concentrate substances suspended in a liquid by utilizing centrifugal force. This separation relies on the varying sedimentation rates of particles when exposed to a centrifugal field. Factors such as size, density, and shape influence the sedimentation rate of these particles. A centrifuge is a device that creates centrifugal force by rapidly spinning the fluid, thereby separating the particles.

    

Principle of centrifugation:

Particles in a solution are drawn downward by the gravitational pull of the Earth. This gravitational force is determined solely by the mass of the particles, not by their charge, shape, or chemical makeup. Due to the Earth's relatively weak gravitational field, particles with very small masses often remain suspended because of random thermal motion. Therefore, forces significantly stronger than Earth's gravity are necessary to achieve noticeable sedimentation of such small masses. These stronger forces can be achieved through centrifugation, where centrifugal forces are applied to enhance the sedimentation of these particles. A centrifuge accomplishes this by generating centrifugal forces up to 1,000,000 times greater than the force of gravity.

    Centrifugal force 

$${\displaystyle F=m{\omega }^{2}r}$$

where ,᭙ is angular velocity in radians per second,

r is distance from the center of rotation of the particle, 

m is mass particles.

Types of Centrifugation   

1. Differential Centrifugation: Differential centrifugation represents the most basic type of centrifugation. In a suspension, particles with varying densities or sizes will settle at different speeds, with the largest and most dense particles settling first, followed by those that are smaller and less dense. The application of centrifugal force can enhance these sedimentation rates.
2.  Rate Zonal Centrifugation: Rate zonal centrifugation, also known as velocity centrifugation, is employed to separate particles based on differences in their sedimentation rates. This separation is determined by the size or density of the particles. While the sedimentation rate is significantly affected by the size (mass) and density of the particles, even minor differences in shape can influence the rate of sedimentation. Rate zonal centrifugation method , materials used for preparation of density gradients are sucrose, glycerol, ficoll .  
3. Isopycnic Centrifugation:  Separates particles based solely on density and is independent of shape and size of particles.
4. Ultracentrifugation: a high-speed method  for separating small biomolecules such as proteins, ribosomes, and viruses.

Comparison: Rate-Zonal vs Differential Centrifugation

Feature	Rate-Zonal Centrifugation	Differential centrifugation
Basis of separation	Size and shape	Density and Size
Use of Density Gradient	yes, preformed gradient	No
Resolution	High	LOW
Risk of contamination	low	high