Deoxyribonucleic acid. The Crick and Watson Model

The first information about the chemical properties of deoxyribonucleic acid dates back to 1868. In the 20th century, by the beginning of the forties, it was proved that the molecule is a linear polymer. Monomer units are nucleotides, which consist of a nitrogenous base, a phosphate group and pentose (a five-carbon sugar).

Deoxyribonucleic acid can have a base of two types: pyrimidine (thymine (T) and cytosine (C)) and purine (adenine (A) and guanine (G)). The nucleotide is joined by phosphodiester bonds.

Biologists Creek and Watson in 1953, based on 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, which are formed between complementary (mutually corresponding) bases in opposite chains. In this case, the pairs are formed only as follows: adenine-thymine, guanine-cytosine. Stabilization of the first is carried out 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 mn.p. And so on, respectively. Thus, deoxyribonucleic acid of human chromosome is represented by one double helix. Its length is 263 m.

DNA denaturation (melting) is a process in which a regular double helix of a linear molecule passes into a coil-like state. During melting, the double-helix molecule is divided into independent chains. The temperature at which half of the Deoxyribonucleic acid is melted is the melting point. It depends on the qualitative molecular composition.

As already mentioned above, G-C pairs are stabilized by three, and pairs of A-T by two hydrogen bonds. Accordingly, the higher the proportion of the first pairs, the more stable the molecule will be. At denaturation with a wavelength of 260 nm, the absorption of light 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 form between the complementary chains, a spiral structure identical to the native one (the original one) may appear. This method of DNA to renaturation and denaturation is based on the method of hybridization of molecules. It is used in the study of the structure of nucleic acids.

The double-helix molecule, carrying the genetic data, must meet two main requirements. First, it must replicate (reproduce) with high accuracy, and second, encode the synthesis of protein molecules. Deoxyribonucleic acid, the model of which has been 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 stage of replication, thus, a pair of daughter molecules with a nucleotide sequence identical to the one in the original DNA molecule arises . In addition, this chain of the structural gene in the encoded protein specifies the amino acid sequence.

Since the discovery of DNA and the principle of complementarity, the processes that are responsible for deciphering hereditary data and regulation in the synthesis of gene substances have been established. In addition, the theory of recombinant molecules also developed.