Nucleotide Codon Optional

Nucleotides codons

The nucleotide of a codon is the base that occupies a specific place in the codon and is part of the transfer RNA. The codon nucleotides are adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U).

According to the Watson-Crick principle of base complementarity, when two strands of DNA or RNA are connected to each other, the base pairs A - T, G - C and Y - A are connected.

Codons

Codons are sequences of nucleotides located on transfer RNA that correspond to a specific amino acid residue in a protein molecule. Each codon consists of three nucleotides. Typically, codons are designated by three-letter abbreviations.

Important characteristics of codons are their ability to encode an amino acid and their frequency of use in protein molecules. Codons coding for the same amino acid are called synonymous.

Optional and obligatory codons

There are two types of codons: mandatory and optional. Required codons always code for the same amino acid. For example, in the insulin protein, the UAU codon will always code for the amino acid phenylalanine.

However, there are also optional codons. An optional codon is a codon that can code for one or more different amino acids, depending on which codon is next to it in the chain.

For example, the AUG codon codes for the amino acid methionine, but can also code for other amino acids such as valine and isoleucine. The CUG codon can code for three amino acids: glutamine, arginine and proline.

There are also codons that can code for only one amino acid.

Optional nucleotide codons are nucleotide bases that are usually found in protein codons and perform the function of hydrogen bonds for the correct assembly of amino acids into the primary structure of the protein. However, some nucleotides can be replaced by others without affecting the codon's ability to code for a specific amino acid.

It is known that each triplet encodes a specific amino acid and the order of these triplets determines the unique sequence of amino acids corresponding to a specific protein. However, the nucleotide base located in the first or last place of the codon rarely plays a significant role in the formation of the peptide bond and can be replaced by any other nucleotide base without changing the amino acid sequence of the protein. Such nucleotides are often considered insignificant or optional in the practice of protein analysis. An optional nucleotide residue is a nucleotide that is part of a codon and usually serves as the basis for a hydrogen bond in that codon. . Facultative means that this residue can be replaced by a non-facultative (obligatory) residue without changing the ability of the synthesized protein to consist of amino acids. This difference is sometimes referred to as the optional remainder requirement.

For example, in DNA, the nucleotide sequence TaATacyl contains five optional residues: the fourth (cytosine, designated by the letter A in the coding table