The genetic code is a special encryption of hereditary information using nucleic acid molecules . Based on this encoded information, genes appropriately control the synthesis of proteins and enzymes in the body, thereby determining metabolism. In turn, the structure of individual proteins and their functions is determined by the location and composition of amino acids - structural units of a protein molecule.
In the middle of the last century, genes were identified that are separate sections of deoxyribonucleic acid (abbreviated as DNA). The nucleotide links form a characteristic double chain assembled in the form of a spiral in DNA molecules .
Scientists have found a connection between the genes and the chemical structure of individual proteins, the essence of which is that the structural arrangement of amino acids in the protein molecules fully corresponds to the order of nucleotides in the gene. Having established this connection, scientists decided to decipher the genetic code, i.e. establish the laws of conformity of the structural orders of nucleotides in DNA and amino acids in proteins.
There are only four types of nucleotides:
1) A - adenyl;
2) G - guanyl;
3) T - thymidyl;
4) C - cytidyl.
The composition of proteins includes twenty types of basic amino acids. It was difficult to decipher the genetic code, since there are much fewer nucleotides than amino acids. In solving this problem, it was suggested that amino acids are encoded by various combinations of three nucleotides (the so-called codon or triplet).
If you count all the possible combinations, then there will be 64 such triplets, that is, three times more than amino acids - an excess of triplets is obtained.
In addition, it was necessary to explain how the triplets are located along the gene. So there were three main groups of theories:
1) triplets follow each other continuously, i.e. form a continuous code;
2) triplets are arranged with alternating "meaningless" sections, i.e. so-called “commas” and “paragraphs” are formed in the code;
3) triplets can overlap, i.e. the end of the first triplet may form the beginning of the next.
Currently, they mainly use the theory of code continuity.
Genetic code and its properties
1) The triplet code - it consists of arbitrary combinations of three nucleotides that form the codons.
2) The genetic code is redundant - this is a consequence of its tripletness. A single amino acid can be encoded by several codons, since the codons, according to mathematical calculations, are three times more than amino acids. Some codons perform certain termination functions: some may be “stop signals” that program the end of the production of the amino acid chain, while others may indicate the initiation of code reading.
3) The genetic code is unique - only one amino acid can correspond to each codon.
4) The genetic code is collinear, i.e. the nucleotide sequence and the amino acid sequence clearly correspond to each other.
5) The code is written continuously and compactly; there are no “meaningless" nucleotides in it. It begins with a certain triplet, which is replaced by the next without a break and ends with a terminating codon.
6) The genetic code is universal - the genes of any organism encode information about proteins in exactly the same way. It does not depend on the level of complexity of the organization of the organism or its systemic position.
Modern science suggests that the genetic code arises directly during the nucleation of a new organism from bone matter. Random changes and evolutionary processes make any code possible, i.e. amino acids can be rearranged in any sequence. Why did this kind of code survive during evolution, why is the code universal and has a similar structure? The more science learns about the phenomenon of the genetic code, the more new puzzles arise.