Nucleic acids, polynucleotides, are high-molecular biologically important compounds; are a necessary part of every cell of a living organism.
Nucleic acids are polymers of nucleotides. Each nucleotide consists of a purine or pyrimidine base, a carbohydrate residue - ribose or deoxyribose, and a residue of phosphoric acid. The nucleotides are interconnected in long chains through residues of phosphoric acid. All nucleic acids are divided into two main types:
1) ribonucleic acids (RNA), which contain carboxylic acid as a carbohydrate , and as bases - adenine (A), guanine (D), cytosine (C) and uracil (U);
2) deoxyribonucleic acids (DNA), which instead of ribose contain deoxyribose and instead of uracil thymine. In addition, nucleic acids contain relatively small amounts of the so-called minor (rare) bases, which are, as a rule, derived from those listed above. An RNA molecule is usually a single polynucleotide chain, often coiled into bizarre shapes. DNA has the structure of a double helix, in which complementary bases (adenine with thymine and guanine with cytosine) are paired with each other. The principle of complementarity is very important for the reproduction of nucleic acids in the body. Due to this principle, a complementary polynucleotide DNA chain is synthesized on the DNA template (during DNA biosynthesis - replication) or RNA (in the process of RNA synthesis - transcription).
RNA biosynthesis occurs under the action of the enzyme RNA polymerase from nucleoside triphosphates with the elimination of pyrophosphate and the combination of nucleotides in a chain complementary to the DNA template. DNA replication occurs similarly under the action of DNA polymerase from deoxyribonucleoside triphosphates.
The DNA of the cell nucleus has a molecular weight of tens and hundreds of millions, and is in the form of deoxyribonucleoproteins - complexes with proteins, mainly of a basic nature - histones and protamines. RNA is subdivided into ribosomal RNA, constituting over 50% of the ribosome material, transporting RNA of relatively low molecular weight, carrying amino acids to ribosomes during protein synthesis, and informational RNA that transmits biological information from DNA to the sites of protein synthesis — ribosomes. Both ribosomes and complexes of messenger RNA with proteins, the informationosomes, are natural ribonucleoproteins (see Nucleoproteins).
Nucleic acids provide storage, transfer and reproduction of biological information, since the specific structure of nucleic acids, consisting in a unique sequence of nucleotide residues in the polynucleotide chain, causes the transfer of inherited traits, as well as synthesis of certain, individual proteins in the body (see). See also Genetics, Heredity.