If a four nucleotide sequence code for an amino acid instead of three, theoretically how many unique amino acids could be coded by such a system:-

• Central dogma of molecular biology states that flow of genetic information takes place from DNA to RNA to proteins.
• Transcription of DNA to RNA is based on the complementarity of their strands.
• However, no such complementarity exists between the RNA and the proteins for translation to take place.
• Evidences show that changes in nucleic acids also caused changes in the amino acids of the proteins.
• This suggested the existence of a Genetic Code that directs the synthesis of amino acids that form the proteins.
• It was George Gamow who suggested that if the 4 nitrogen bases of nucleic acids have to code for the 20 non-essential amino acids produced in the body, the code should constitute a combination of bases.
• The nitrogen bases include Adenine (A), Guanine (G), Cytosine (C) and Uracil (U) for an RNA.
• A permutation combination of 2 bases would give: 4² = 16 amino acids only.
• So, it has to be a combination of 3 bases giving: 4³ = 64 codons.

Important Points

• From the above points, we can get the formula as:

(No. of N-bases available)^{No. of bases in each sequence code} = No. of codons

• Therefore, if we take 4 nucleotide sequence code,

No. of codons = 4⁴ = 256

• Similarly if we take a 5 sequence code, we will get 4⁵ = 1024 codons.
• Please note that these are only theoretical possibilities.