Molar Concentration Welcomes Avogadro in Postgenomic Analytics

At the end of the 18^th century the physicist Amedeo Avogadro formulated the law, which subsequently allowed establishing one of the fundamental constants called Avogadro's number. The Avogadro’s number defined the number of molecules in one grammolecule. The Avogadro’s constant (N_A) is expressed in the unit mol⁻¹ and used in the International System of Units (SI), instead of the dimensionless Avogadro’s number, which counts for the number of molecules.

For a century the Avogadro’s number and molar concentration existed in parallel. These two terms were rarely used together to characterize the number of molecules of any substance in a solution. In the early 21st century the situation changed due to the emergence of genomics and its derivatives – transcriptomics and proteomics. Postgenomic science aroused a necessity to characterize the number of molecules of DNA (for genome), RNA (for transcriptome), and proteins (for proteome) in the copies of molecules in a biological sample. Combining the concepts of the Avogadro’s number and molecular concentration it was possible to revisit the notion of protein content in a solution (and cells) using number of molecules instead of chemistryimposed concentration units. The reverse Avogadro’s number was introduced for recalculating the concentration of substances in a solution to the copy numbers, i.e. the determination of the number of entities of a certain biomacromolecule in a cell volume or in a biofluid, for example, in blood plasma.