DNA, the genetic material, replicates and undergoes a process known as transcription to synthesize RNA molecules. The genes or small regions in the DNA code for RNA. Four nucleotides constitute the double helix structure. Adenine, guanine, thymine, and cytosine are nucleotide bases present in the DNA structure. An RNA molecule consists of uracil instead of thymine. RNA is mainly involved in synthesizing proteins. Primary to quaternary structures of proteins are amino acid-dependent. Therefore, proteins also have sequences like DNA and RNA. Nucleic acids have gene sequences while proteins have amino acid sequences. Most of the proteins are not self-synthesizing because they are RNA dependent. A, C, G and U in an RNA molecule are not just letters but are capable of creating huge sentences. Meaning, A, C, G, and U nucleotides together form three-letter codes to generate codons. Thus an amino acid sequence is specified by these four nucleotides.

The concept of the codon is very simple to understand. Imagine any three of the above nucleotides together, say AUG. Thus, AUG becomes a codon. It can code for an amino acid or a signal. AUG is known as an initiation codon. It is involved in the initiation of translation (protein synthesis). Thus three nucleotide bases come together in triplets and generate total 64 codons. Why only three letter code? The logic behind cells utilizing three letter code instead of one or two letter code is to create 20 different amino acids. Just one or two letter codes won’t be sufficient. A code with more than three bases would possibly synthesize undesirable products. Thus a three letter code fits perfect, in the picture.