The implementation of the genetic material of any cell is based on the synthesis of a specific set of proteins recorded in the DNA sequence. This information is transmitted through the molecules of messenger RNA (mRNA), on the basis of which amino acid chains are built. Since proteins and nucleic acids are chemically completely different, the mechanism of complementary conjugation is carried out with the participation of transport RNAs that interact with the matrix chain through the codon-anticodon system.
Features of decoding mRNA sequence
In addition to the difference in the chemical nature of proteins and nucleotides in the translation of genetic information, there is another problem - a quantitative mismatch in the diversity of units. The RNA molecule is formed by only four types of nucleotides, while the polypeptide chain can include up to 20 types of amino acids. For this reason, the coding unit of the RNA matrix is not one nucleotide, but three. This sequence is called a triplet.
Different combinations of nucleotides in the triplet give 64 combinations, which even exceeds the required number of options equal to 20. This phenomenon indicates the redundancy of the genetic code.
Triplet system
Another name for the RNA sense triplet is the codon. This sequence interacts with its complementary anticodon contained in the transport RNA molecule, which corresponds to a specific amino acid. Thus, the sequence of units in the primary structure of the protein is determined.
The triplet system was decrypted in the early 1960s.
What is a codon?
Since the genetic code is redundant, some amino acids are designated not by one, but by several codons. In addition, there are triplets that do not contain information about the link of the protein sequence. These codons are needed to stop the translation process. These include UAA, UAG and UGA.
Thus, a codon is a three-unit sequence of nucleotides of messenger RNA that denotes either an amino acid or a translation stop. The values of all triplets are listed in the genetic code table.
In addition to three stop codons, there is also a triplet that signals the beginning of the mRNA translating region, AUG. However, unlike termination sequences, this codon contains information about the amino acid (methionine). The genetic code is universal for all types of organisms.
The interaction of codons with transport RNA
There are 2 functional sites in the tRNA molecule, one of which interacts with messenger RNA, and the other binds to the amino acid. Anticodon contains nucleotides that are complementary to the mRNA codon sequence. The nature of the interaction is similar to transcription, only pairing occurs in groups of 3 nucleotides.
Some tRNAs do not require exact complementary correspondence not with all links of the triplet, but only with the first two. Tolerance to the third nucleotide in the codon is called swing, due to which one tRNA can bind to several types of triplets that differ from each other only in the link in the last position.