The vital functions of the cells of living organisms are based on the functions of biological polymers: nucleic acids, carbohydrates, proteins and lipids. Biopolymers consist of monomers, hydrocarbon structures, which also include nitrogen, oxygen, sulfur and phosphorus.
In the 19th century, a study was begun of the structure of the substances that make up a living cell, but the functions of DNA, proteins, RNA and their structure were finally determined in the 20th century.
In 1868, Friedrich Mischer isolated a phosphorus-containing substance from the nuclei of white blood cells and called it nuclein. Then Richard Altman in 1889 determined that this substance consists of a special acid and protein. It was then that they first heard about the term "nucleic acid." However, the establishment of nucleic acid function was still a long way off.
DNA - deoxyribonucleic acids - these are the largest biological polymers, consisting of hundreds of monomers - deoxyribonucleotides. In addition to sugar (deoxyribose), they include 4 types of nucleotides: adenine - A, thymidine - T, cytosine - C, guanine - G.
At first, DNA was considered a nucleic acid of animal origin, since it was isolated from the thymus of animals, and RNA isolated from wheat seedlings was plant. It was believed that finally the biochemical difference of the cells of the races was found
tenii and animals. However, in the middle of the twentieth century it was established that RNA and
DNA are part of all cells.
The structure of nucleic acids was directly studied by Erwin Charguff, who in 1953 found that the nucleotides that make up the acids of the same name form pairs with a strict regularity.
One pyrimidine and one purine bases always come into contact, G = C, A = T. That is, adenine binds to thymidine, and guanine to cytosine.
Moreover, for the function of DNA, it is essential that the bond in the first case is provided by 2 hydrogen pairs, and in the second - by three.
Charguff's rule turned out to be the basis on which Watson and Crick built the DNA double helix structure .
In this molecule, as well as in protein molecules, primary, secondary and tertiary structures are distinguished.
The primary structure is a linear sequence of monomers in one chain.
Of course, DNA does not occur in the form of a single chain in nature, but here we are talking about the primary structure of a biopolymer, which determines all its properties.
The secondary structure is a spatial characteristic of a biopolymer. In the case of DNA, it represents two polynucleotide chains, each of which is twisted into a spiral to the right, and both of them are simultaneously twisted clockwise around a common axis. These chains are held together by
hydrogen bonds. The tertiary structure of DNA is determined by the further spiralization of the molecule.
A giant step forward was made with the discovery that the functions of DNA consist in the transfer and storage of genetic information. DNA contains a hereditary program about the structure of proteins specific to each organism. Together with RNA molecules, they transmit hereditary information from organism to organism. The functions of DNA also include the implementation of genetic information. They participate in the processes of transcription, replication and translation, thereby ensuring the synthesis of a variety of proteins.