^{Genomics and Molecular Biology}

The researchers working with high-throughput methods of genomics, transcriptomics, and proteomics reconsider the concept of concentration and evaluate the data obtained in the number of copies of biomacromolecules. Measurement of copy number refl ects a steady trend in increasing the sensitivity of postgenomic analytical methods, up to the level of a single molecule. In this paper we review the physical meaning of the terms molar concentration and Avogadro’s number to establish a relationship between them. Th e relationship between the molar concentration and the number of copies of

that same macromolecule in a certain volume is set through the reverse Avogadro’s number, the value of which (≈10-24 Ðœ) characterizes the molar concentration of a single molecule in 1 liter. Using the reverse Avogadro’s number, we deal with situations in analyzing homogeneous biological solutions and heterogeneous cellular material.