Biomics

DNA has been known for more than 150 years, and during this time, many methods have been developed for isolating this biopolymer from various sources. At the same time, the vast majority of methods for DNA isolation involve its precipitation from aqueous-saline solutions in which DNA is surrounded by polar water molecules, the positively charged part of the dipole of which interacts with negatively charged phosphate groups of DNA, contributing to its solubility. The most commonly used DNA precipitators are ethanol and isopropanol, which do not interact with the polar groups of nucleic acids as strongly as water, which, coupled with partial neutralization of the charge by salts, leads to a decrease in DNA solubility and precipitation. Since DNA is a polyanion due to phosphoric acid residues, the neutralization of its charge with the help of polycations, which serve as various compounds, including spermidine, spermine, hexaamminecobalt chloride, polyethylenimine and others, leads to DNA compactization and aggregation, leading to precipitation. Similar processes leading to a decrease in DNA solubility, up to the formation of a precipitate, are caused by compounds such as high-molecular-weight polyethylene glycol, polyvinylpyrrolidone, Ficoll. Moreover, non-alcoholic DNA precipitation/reprecipitation is in high demand in cases where it is necessary to change the buffer or get rid of the ingredients of the previous enzymatic reaction, but the addition of alcohol cannot be performed. For a long time, the determination of phosphorus, the content of which should ideally be 9.3%, served as an indicator of the purity of the isolated preparations. Later, to determine the purity of the isolated DNA, measurement of optical density and A_260/A280 and A_260/A230 indicators became common, indicating the degree of contamination of preparations with proteins and polysaccharides, respectively. In the last quarter of the last century, it became necessary to control the size of the extracted DNA using gel electrophoresis. At the same time, not only the maximum size is important, but also the homogeneity of the DNA preparation, which implies the absence of many short fragments in it, which may interfere with some experiments, including methods of monomolecular DNA sequencing designed for long and ultra-long reads. In such cases, it is possible to fractionate DNA molecules by size by simply reprecipitating them under the action of non-alcoholic agents, achieving primary deposition of high-molecular-weight DNA.

DNA isolation, DNA precipitation, DNA fractionation, high-molecular-weight DNA

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