Svedberg unit

Svedberg unit (S), named after the Swedish chemist Theodor Svedberg, is a non-SI unit for sedimentation rate. The sedimentation rate is used to measure the rate at which a particle sediments when subjected to centrifugal force. It is commonly used in ultracentrifugation to describe the sedimentation rate of particles in a centrifugal field. The Svedberg unit is particularly significant in the study of biomolecules, such as proteins, ribosomes, and nucleic acids, where it helps in understanding their size, shape, and structure.

Definition

The Svedberg unit is defined as 10^-13 seconds (10 picoseconds). It is a measure of a particle's sedimentation velocity in a centrifuge. The sedimentation velocity is influenced by the size, shape, and density of the particle, as well as the density of the medium in which the particle is suspended. A higher Svedberg value indicates a larger or denser particle that sediments faster.

Application

In biochemistry and molecular biology, the Svedberg unit is essential for the separation and analysis of biomolecules. During ultracentrifugation, molecules are separated based on their sedimentation rates, allowing researchers to purify and study various components of cells. For example, ribosomes are often classified by their sedimentation rates, with eukaryotic ribosomes being 80S and prokaryotic ribosomes being 70S, where 'S' stands for Svedberg units.

Measurement

The sedimentation rate of a particle is measured using an ultracentrifuge, a specialized piece of equipment capable of generating extremely high centrifugal forces. The sedimentation coefficient (S) is calculated by dividing the sedimentation velocity by the acceleration applied to the sample. This coefficient is then expressed in Svedberg units, facilitating the comparison of sedimentation rates across different experiments and conditions.

Significance

Understanding the sedimentation rate of particles is crucial in the study of molecular structures and interactions. The Svedberg unit provides a standardized way to describe the sedimentation characteristics of particles, enabling scientists to deduce their physical properties and to purify specific biomolecules for further study. This has implications in various fields, including the development of pharmaceuticals, the study of genetic material, and the understanding of cellular processes.

Limitations

While the Svedberg unit is a valuable tool in molecular biology and biochemistry, it is important to note that sedimentation rates can be affected by several factors, including temperature, viscosity of the medium, and the shape of the particle. Therefore, sedimentation rates are specific to the conditions under which they were measured and may not directly correlate to the mass or size of the particles.

Svedberg unit Resources
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