Analytical ultracentrifugation is a classical technique that has played a critical role in laying the foundations for modern molecular biology. Among its achievements is the
demonstration that proteins are macromolecules rather than complexes of smaller units, and direct support for the semiconservative replication mechanism of DNA as proposed
by Watson and Crick. Unlike techniques such as SDS PAGE or gel permeation hromatography, analytical ultracentrifugation can be used to determine absolute molecular weights
without the use of molecular weight standards or interference from the sieving matrix used for separation.