Structure of human DNA

The existence of living matter is associated with the presence of nucleic acids. F. Misher first isolated these substances from the nuclei of leukocytes (1869). Later they were found in all cells of living organisms (humans, animals, plants, bacteria and viruses).

Nucleic acids are the prostatic groups of nucleoproteins. Nitrous bases (adenine, cytosine, guanine, uracil and thymine), pentoses (deoxyribose, ribose) and phosphate acid are obtained by hydrolysis of nucleic acids. Given the biochemical composition, the nucleic acids are classified into deoxyribonucleic (DNA) and ribonucleic (RNA) acids. The structure of human DNA includes deoxyribose, RNA - ribose. These acids differ in the structure of molecules, the composition of nitrogenous bases, cellular localization, and of course, functions. Biocompounds, the molecule of which consists of a purine or pyrimidine base and monos (ribose or deoxyribose), are called nucleosides. The name of the nucleoside is determined by the nitrogenous base contained in it. Thus, the nucleoside, which includes the adenine molecule in its structure, is called adenosine, thymine - thymidine, uracil - uridine, cytosine - cytidine, guanine - guanosine. Depending on the monosaccharides (pentose), which are part of the molecules, distinguish between ribonucleosides and deoxyribonucleosides.

Human DNA is the chemical basis of genes in which the hereditary information of the body is concentrated. It is localized mainly in the nuclei of cells, mainly in chromosomes. During the hydrolysis of DNA, nucleotides are formed: deoxyadenyl (A), deoxyguanil (D), deoxycytidyl (C) and thymidyl (T) acids. Occasionally, other derivatives of purines and pyrimidines, minor bases, are found in the nucleotide composition: 5-hydroxymethylcytosine (in bacteriophages), 5-methylcytosine (in thymus tissues), and others. Nucleotides are connected to the polynucleotide chain (DNA) by oxygen bridges formed by hydroxyl - a phosphate acid residue of one nucleotide and hydroxyl group at the third carbon atom of the deoxyribose residue of the second nucleotide.

The nucleotide sequence in the human DNA molecule is studied by sequencing (English seguence). For this, a sequencer is used, which, based on computer analysis, establishes a nucleotide sequence (up to one hundred units).

The number of nucleotides in the human DNA molecule is 25,000 - 35,000 or more, and the molecular weight is from several million to 2-5 billion. DNA molecules can be "seen" in an electron microscope. The absolute number of nucleotides of four species (A, G, C, and T) in DNA molecules of different origin varies in wide ranges.

Primary structure of DNA

F. Crick and D. Watson in 1953 found that the deoxyribonucleic acid molecule is a double helix of polynucleotide chains twisted around its axis. The spiral resembles a spiral staircase in which handrails are formed by deoxyribose residues, connected by phosphoric ester bonds of type 3 - 5, and steps - by nitrogenous bases. Adenine is connected by hydrogen bonds with thymine, guanine - with cytosine. The configuration of deoxyribonucleic acid can be compressed and stretched. This is the secondary structure of DNA. A single-stranded DNA molecule was found in some bacteriophages. For the deoxyribonucleic acid molecule, a tertiary structure is also characteristic, which is formed due to the reunification of the double-stranded and circular DNA form, followed by the formation of helical and supercoiled structures.