Theodor Svedberg was a physical chemist whose work significantly affected the development of biochemistry in the twentieth century. He was born in Flerang, Valbo, in Sweden on August 30, 1884. He was educated at the Koping School and Orebro High School and earned B.A., M.S., and Ph.D. degrees at Uppsala University (the latter in 1908). His hobbies were painting and botany. He chose chemistry as his life's work because he believed chemistry to be a means of greater understanding of biological systems. Svedberg spent his entire professional life associated with Uppsala University, first as an assistant at the Chemical Institute in 1905 and then as a professor of physical chemistry starting in 1912. He was awarded a number of international prizes, including the Nobel Prize in chemistry in 1926. This honor was awarded for his groundbreaking work in the chemistry and physics of disperse systems .
Svedberg's primary focus as a physical chemist was the field of colloid chemistry. Colloids are mixtures of very small particles that when dispersed in solvents are not dissolved, but are held in suspension by various actions of the solvent. Svedberg and his collaborators studied the interaction of colloid suspensions with light and their sedimentation processes. These studies showed that the gas laws could be applied to colloidal systems. Svedberg's Ph.D. thesis on the diffusion of platinum colloidal particles elicited a response from Albert Einstein, since it supported Einstein's theory concerning the Brownian motions of colloidal particles.
A more detailed study of the sedimentation of colloidal disperse systems required Svedberg's 1921 invention of the ultracentrifuge. This centrifuge is similar in principle to a regular laboratory centrifuge except that it rotates at very high angular velocities to provide centrifugal forces as high as 1,000,000 times the force of Earth's gravity. This force is capable of causing colloidal particles to separate into sedimentation bands of varying distances from the center of the centrifuge according to particle size. These bands are observed while the machine is running by photographing the bands, a technique called Schlieren photography. The sedimentation process of colloidal dispersions under these conditions is related to both the shape and mass of the particles. Homogeneous solutions of very large molecules such as carbohydrates, proteins, nucleotides (such as DNA ), and manmade polymers also respond to high forces according to shape and molecular mass.
In the early days of modern biochemical studies, the overall structure of proteins was not well understood. There were two major schools of thought. One theory posited that proteins are agglomerations of small molecules (Svedberg's theory, consistent with his colloid studies), and the second theory was that proteins are very large molecules. In 1921 Edwin Cohn of Harvard University, who subscribed to the large molecule theory, challenged Svedberg to subject a purified protein to the ultracentrifuge. If the protein were made up of smaller molecules, it would separate into a number of fractions with small molecular weights. If the protein was composed of only one type of very large molecule, the ultracentrifuge would show only one fraction of very high molecular weight. To Svedberg's surprise, the experiment showed that there was only one type of molecule and that proteins are, in fact, made up of a single sort of large molecule. This was a very important result in the understanding of proteins and other large molecules.
Although Svedberg is remembered for his very important work in colloids and artificial rubber, he must also be remembered as a scientist who was willing to test his own theory rigorously and change his point of view when experiment indicated a theory to the contrary.
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