Genetic Code Explanation

The arrangement of nucleotides within DNA establishes the sequence of amino acids in a polypeptide. This sequencing, mirrored in mRNA, dictates the arrangement of amino acids. This interconnection between bases and amino acids is referred to as the genetic code. It may seem necessary to have a unique code for each of the 20 amino acids. However, can a set of four nucleotides offer sufficient permutations to represent these 20 amino acids? If we were to use individual base codewords, the resulting protein could encode only four amino acids. If pairs of bases were used to code for a single amino acid, then 16 amino acids could be accommodated in protein structures. Yet, if each codon were composed of three bases, a total of 64 codons would emerge—more than ample to represent the 20 amino acids.

Genetic Codons 

Discovery of the Genetic Code

During 1961, Marshall Nirenbery and J. Heinrich Matthei synthesized RNA using solely Uracil. The ensuing protein solely consisted of the amino acid phenylalanine, revealing that the codon for phenylalanine is UUU. Subsequently, Nirenberg and Philip Leder devised a cell-free system capable of translating three nucleotides at once. This advancement facilitated the assignment of an amino acid to each RNA codon.

Key Characteristics of Codons

Degeneracy: The genetic code exhibits "degeneracy," implying that numerous amino acids possess multiple codons.

Unambiguity: The genetic code is unambiguous; each triplet codon carries a singular meaning.

Initiation Codon: Singular initiation codon, denoted AUG.

Termination Codons: Three distinct stop signals: UAA, UAG, UGA.

Universal Base Triplets: The triplet coding for an amino acid is consistent across all organisms.

Non-Overlap: An mRNA sequence commencing with AUGAGCGCA is not read as AUG/UGA/GAG. Rather, it is read as AUG/AGC/GCA.