Svedberg

Beckman-Coulter ultracentrifuge XL-100K -01

Svedberg (S) is a non-SI unit used to measure the rate of sedimentation during centrifugation of suspensions. It is named after the Swedish chemist Theodor Svedberg (1884–1971), who was awarded the Nobel Prize in Chemistry in 1926 for his work on colloids and proteins using the ultracentrifuge, an instrument he invented. The Svedberg unit reflects how fast a particle settles to the bottom of a solution when subjected to centrifugal force, a property that is crucial in the separation and analysis of biomolecules such as proteins, nucleic acids, and ribosomes.

Definition

The Svedberg unit is defined as 10^-13 seconds (10 picoseconds). It is a measure of a particle's sedimentation coefficient, which is the ratio of a particle's sedimentation velocity to the applied acceleration causing the sedimentation. The sedimentation velocity is influenced by factors such as the size, shape, and density of the particle, as well as the density and viscosity of the medium in which the particle is suspended.

Application

In biochemistry and molecular biology, the Svedberg unit is particularly useful for the characterization of macromolecules. For instance, ribosomes, which are essential for protein synthesis in living cells, are often identified by their sedimentation coefficients, with the 70S ribosomes of prokaryotes and the 80S ribosomes of eukaryotes being common examples. The "S" in these designations stands for Svedberg units, indicating the rate at which these complexes sediment in a centrifugal field.

The Svedberg unit is also used in the purification and analysis of proteins and nucleic acids. By subjecting a mixture of molecules to ultracentrifugation, researchers can separate components based on their sedimentation coefficients, allowing for the study of individual macromolecules in detail.

Measurement

The measurement of sedimentation coefficients is performed using an ultracentrifuge, which can generate centrifugal forces many thousands of times greater than the force of gravity. Samples are placed in a rotor and spun at very high speeds, and the rate at which particles move towards the bottom of the tube is measured. This rate is then used to calculate the sedimentation coefficient of the particles.

Significance

The Svedberg unit has been instrumental in the field of molecular biology, enabling scientists to study the structure and function of various biomolecules. It has facilitated the discovery of key biological processes and the understanding of molecular mechanisms underlying health and disease.

See Also

• Centrifugation
• Colloid
• Protein
• Nucleic acid
• Ribosome
• Theodor Svedberg

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