The first information about the chemical properties of deoxyribonucleic acid dates from 1868. In the 20th century, by the beginning of the forties, it was proved that the molecule is a linear polymer. Nucleotides, which consist of a nitrogenous base, a phosphate group and pentose (five-carbon sugar), act as monomer units.
Deoxyribonucleic acid can have a base of two types: pyrimidine (thymine (T) and cytosine (C)) and purine (adenine (A) and guanine (G)). The nucleotide compound is carried out using phosphodiester bonds.
Biologists Crick and Watson in 1953, taking as the basis x-ray structural analysis of DNA crystals, came to the conclusion that the native molecule consists of a pair of polymer chains forming a double helix. Polynucleotide chains wound on each other are held together by hydrogen bonds that form between complementary (mutually corresponding) bases in opposite chains. In this case, pairs are formed only as follows: adenine-thymine, guanine-cytosine. The first is stabilized by two, and the second pair by three hydrogen bonds.
Double-stranded deoxyribonucleic acid has a length calculated by the number of pairs of mutually corresponding nucleotides (bp). For those molecules that consist of millions and thousands of pairs, units of m.s. and so on, respectively. So, deoxyribonucleic acid of a human chromosome is represented by one double helix. Its length is 263 m.p.
DNA denaturation (melting) is the process by which a regular double helix of a linear molecule transforms into a glomerular state. During melting, the double-stranded molecule is divided into independent chains. The temperature at which half of the deoxyribonucleic acid is molten is the melting point. It depends on the qualitative molecular composition.
As mentioned above, G – C pairs are stabilized by three, and – T pairs by two hydrogen bonds. Accordingly, the higher the proportion of the first pairs, the more stable the molecule will be. With denaturation with a wavelength of 260 nm, light absorption increases. This hyperchromic effect makes it possible to provide control over the state of the secondary molecular structure. If the molten acid solution is slowly cooled, then weak bonds can again form between the complementary chains, and a spiral structure identical to the native (original) one may arise. The method of hybridization of molecules is based on this ability of DNA to renature and denature. It is used in the study of the structure of nucleic acids.
A double-helix molecule, being a carrier of genetic data, must meet two main requirements. Firstly, it must be replicated (reproduced) with high accuracy, and secondly, it must encode the synthesis of protein molecules. Deoxyribonucleic acid, the model of which was described by Crick and Watson, fully meets these requirements. It is established that in accordance with the principle of complementarity, each chain in a molecule can be a matrix for the formation of a new mutually corresponding chain. As a result of one replication step, thus, a pair of daughter molecules is created that have a nucleotide sequence identical to that in the original DNA molecule. In addition, this chain of the structural gene in the encoded protein defines the amino acid sequence.
From the moment that the discovery of DNA and the principle of complementarity were made public, processes have been established that are responsible for deciphering hereditary data and regulating the synthesis of gene substances. In addition, the theory of recombinant molecules has also been developed.