Beckman-Coulter ultracentrifuge XL-100K -01

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, a Svedberg unit or svedberg (symbol S, sometimes Sv) is a non- SI metric unit for sedimentation coefficients. The Svedberg unit offers a measure of a particle's size indirectly based on its sedimentation rate under acceleration (i.e. how fast a particle of given size and shape settles out of suspension). The svedberg is a measure of time, defined as exactly 10⁻¹³ seconds (100 fs). For biological macromolecules like ribosomes, the sedimentation rate is typically measured as the rate of travel in a centrifuge tube subjected to high

g-force The g-force or gravitational force equivalent is a Specific force, mass-specific force (force per unit mass), expressed in Unit of measurement, units of standard gravity (symbol ''g'' or ''g''0, not to be confused with "g", the symbol for ...

. The svedberg (S) is distinct from the SI unit sievert or the non-SI unit sverdrup, which also use the symbol Sv, and to the SI unit Siemens which uses the symbol S too.

Naming

The unit is named after the Swedish

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a graduated scientist trained in the study of chemistry, or an officially enrolled student in the field. Chemists study the composition of ...

Theodor Svedberg (1884–1971), winner of the 1926

Nobel Prize The Nobel Prizes ( ; ; ) are awards administered by the Nobel Foundation and granted in accordance with the principle of "for the greatest benefit to humankind". The prizes were first awarded in 1901, marking the fifth anniversary of Alfred N ...

for his work on disperse systems, colloids and his invention of the ultracentrifuge.

Factors

The Svedberg coefficient is a nonlinear function. A particle's mass, density, and shape will determine its S value. The S value depends on the frictional forces retarding its movement, which, in turn, are related to the average cross-sectional area of the particle. The sedimentation coefficient is the ratio of the speed of a substance in a centrifuge to its acceleration in comparable units. A substance with a sedimentation coefficient of 26S () will travel at 26 micrometers per second () under the influence of an acceleration of 1 million gravities (10⁷ m/s²). Centrifugal acceleration is given as ''rω''; where ''r'' is the radial distance from the rotation axis and ''ω'' is the angular velocity in radians per second. Bigger particles tend to sediment faster and so have higher Svedberg values. Svedberg units are not directly additive since they represent a rate of sedimentation, not weight.

Use

In centrifugation of small biochemical species, a convention has developed in which sedimentation coefficients are expressed in the Svedberg units. * The svedberg is the most important measure used to distinguish ribosomes. Ribosomes are composed of two complex subunits, each including rRNA and

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

components. In prokaryotes (including bacteria), the subunits are named

30S The prokaryotic small ribosomal subunit, or 30Svedberg, S subunit, is the smaller subunit of the 70S ribosome found in prokaryotes. It is a complex of the 16S ribosomal RNA (rRNA) and 19 proteins. This complex is implicated in the binding of tr ...

and 50S for their "size" in Svedberg units. These subunits are made up of three forms of rRNA: 16S, 23S, and 5S and

ribosomal protein A ribosomal protein (r-protein or rProtein) is any of the proteins that, in conjunction with rRNA, make up the ribosomal subunits involved in the cellular process of translation. ''E. coli'', other bacteria and Archaea have a 30S small subunit ...

s. * For bacterial ribosomes, ultracentrifugation yields intact ribosomes ( 70S) as well as separated ribosomal subunits, the large subunit ( 50S) and the small subunit (

). Within cells, ribosomes normally exist as a mixture of joined and separate subunits. The largest particles (whole ribosomes) sediment near the bottom of the tube, whereas the smaller particles (separated 50S and 30S subunits) appear in upper fractions.

Naming

Factors

Use

See also

Footnotes

References

External links