The first inhabitants of our planet most likely had a very short life expectancy. The evolutionary direction of all living things went in the direction of increasing the life expectancy of the organism for successful adaptation to environmental conditions, the development of adaptation mechanisms and the possibility of transferring the accumulated experience to subsequent generations. The creation of organic molecules in accordance with the planned plan allowed life on Earth to gain a foothold and begin successful development. The mechanism of matrix storage and transmission of hereditary information has been transformed into a genetic coding system, where the main component is the functional unit of the genetic code.
Central dogma of molecular biology
Heredity is the main biological component of life continuity. Nature has created mechanisms for transmitting and reproducing hereditary information by encoding the composition of proteins in the nucleic acid chain. The functions of nucleic acids (DNA and RNA) are the preservation of information and its transfer to the structure of proteins. And proteins, through metabolic reactions, carry out the phenotypic manifestation of this information. The genetic code is a matrix linear storage of information about the structure of a protein by recording it in triples of nucleotides in a nucleic acid chain. The smallest functional unit of the genetic code containing information on the minimal structural unit of proteins is a triplet of nucleotides in a DNA or RNA chain. Information is transmitted from DNA to mRNA, and from mRNA to other RNA and protein molecules.
Universal coding system
Science took a century to understand the genetic code, and only decades to decipher it. Since the advent of the concept of the structure of the DNA double helix (Watson and Crick, 1953), an understanding of its role as hereditary material has come, and the search for those letters of the alphabet that record information on it has begun. The idea that the functional unit of the genetic code 1 nucleotide did not immediately stand up to criticism. Four complementary nucleotides (adein, guanine, cytosine and thymine) DNA could not encode 21 amino acids of proteins. Mathematicians, physicists and biologists were actively involved in the search for a coding system and quickly found out that a single amino acid encodes a sequence of three nucleotides. Thus, the functional unit of the genetic code is a triplet of nucleotides responsible for the synthesis of one amino acid of a protein. There are 64 triplets (codons), of which 61 are semantic codons (encode amino acids), and the remaining 3 are meaningless. They do not carry information about the amino acid, but act as stop codons that complete or initiate the synthesis of a protein molecule.
A triplet is a functional unit of the genetic code.
A biopolymer nucleic acid molecule consists of monomers - nucleotides. Those, in turn, create continuous DNA with which information is transferred to the mRNA in the process of transcription in accordance with the reading frame, where the triplet of nucleotides has the lowest code value. The reading frame moves unidirectionally, and the genetic code has a clear uniqueness and degeneracy (redundancy).
Unidirectionality and uniqueness
The triplet information is unambiguous, that is, the ratio of 1 triplet -1 amino acid is not variable. An amino acid can be encoded with several triplets, but a specific triplet is a specific amino acid. The reading frame is always directed in one direction, and this is due to the presence of triplets that initiate reading and end it. This preserves the stability of the protein structure. Another property of triplets is non-overlap. This means that the nucleotide is necessarily part of the triplet, but exclusively of only one.
Natural redundancy
The degeneracy (redundancy) of the genetic code is like a margin of safety. It protects the cell from the destructive effects of mutations. Each functional unit of the genetic code can undergo substitutions of 1, 2, and 3 nucleotides in a triplet. Thus, 9 positional substitutions in each triplet, substitutions of each nucleotide for 4-1 = 3 possible options, and as a result we get 61 for 9 = 549 variants of nucleotide substitutions in the triplet. This is much more than is necessary to encode 21 amino acids. This redundancy, or degeneracy, has ensured the biological existence of life and minimizing errors in reading genetic information.
Codon or triplet?
In the literature, a triple of nucleotides, as a functional conglomerate, is called a triplet or codon. What is the difference and is it there? The term "codon" is used in the direct translation process - the transfer of information from RNA to a protein molecule. The term "triplet" is used in a broader semantic context, when describing the reading frame of information with both RNA and DNA.