If you imagine the appearance of a DNA molecule,then it resembles a twisted spiral, which is formed by two polynucleotide chains, which are twisted together and simultaneously around one common axis for them.
As a rule, the structure of DNA is considered within the framework ofsystem analysis, while the main one is a strictly established (for a normal state) order of the relative location of deoxyribonucleoside monophosphates-dNMP, constituting the polynucleotide chains.
In the unmutated cell, the mononucleotides are connectedphosphodiester bonds, while the ends of the polynucleotide chain themselves have two variants of the arrangement of the real groups: at the 5 "end of the chain is a phosphate group, and the OH group is at the 3" end of the chain.
If we consider a molecule consisting of twochains, then the structure of DNA will be such that the polynucleotide chains turn out to be antiparallel to each other. In this case, the chains, in such a structure, will be retained due to the hydrogen bonds that exist between the bases A-T and G-C, lying in the same plane perpendicular to the main axis of the molecule helix. Those hydrophobic interactions that form between the bases of such a molecule ensure the stability of the entire double helix. For such a molecule, the structure of DNA is characterized by the complementarity of polynucleotide chains, but not their identity, since their nucleotide composition differs.
Further, considering what isstructure of DNA, it should be pointed out that each individual molecule is "packed" into its own, strictly unique, separate chromosome. These chromosomes contain a variety of proteins that correspond to strictly defined sequences of the structure of the DNA molecule. These proteins are classified into 2 categories: histones and non-histone proteins. In a complex with the nuclear DNA of cells, these proteins are called chromatin.
Characterizing the structure of the DNA, it should be pointed out thatchromatin consists of five kinds of histones, the combined positive charge of which, provides histones with a very strong connection with DNA. A complex of histones and a specific region of the DNA molecule, which contains 146 nucleotide pairs, interacts, resulting in the formation of nucleosomes.
The molecules of the DNA, which are included in the structure, are nonhystonesrepresent a variety of types of regulatory proteins associated with certain DNA sequences. Also, the structure of the DNA molecule is complemented by enzymes that provide biosynthesis.
To study the structure of DNA and RNA within the framework of system analysis follows only in a complex, that is, when considering the structure of DNA, it is necessary to consider the structure of RNA.
Its primary structure, as well as in the case ofmolecule of DNA, is an algorithm for the alternation of ribonucleoside monophosphates, and it must be taken into account that, in contrast to the DNA molecule, all types of RNA have only one polynucleotide chain. In the structure of the RNA molecule, its individual chains form the so-called "hairpins" - spiral loops, which are created by the bases A-U and G-C and are stabilized due to hydrogen bonds.
As a rule, the average molecule of DNAincludes about 150 million nucleotide pairs, and its length is four centimeters. In laboratory analysis, such molecules are extremely inconvenient for research, because when it is released from the tissue, the molecule is usually highly fragmented and becomes much smaller in size. To eliminate this inconvenience, the PCR method is used in the studies - polymerase chain reaction, within the framework of which selective synthesis of separate sections of the DNA molecule takes place and the fragments necessary for the study are extracted.
