Cistrons are sections of a DNA molecule that encode one functional gene, regulating the operation of the gene in response to the influence of any factors (for example, lighting, temperature, rest period, etc.). The size of a cistron can be from 50 to 20 thousand bp, and if we consider the structure of the protein, then this specific protein is limited to cistrons. In biochemistry, it is customary to distinguish small cistrons (from 1 to 8 amino acids) and large ones (from 9 to 40 amino acids).
When assembling the human genome, one of the most frequently occurring cistrons is called the "structural" cistron. The concept of “structural gene” appeared in connection with the important role of protein structure in their functions. Despite the fact that amino acids are assembled into a polypeptide chain, correctly organizing the sequence of these residues is not enough for the information contained in the sequence of genome letters to be transformed into the structure and function of a complex protein. Therefore, it is necessary to isolate a sequence in the DNA molecule that determines the order of protein blocks. This is the structure of a protein or nucleoprotein. Nucleoproteins are made up of three