Genetic Code

Genetic Code

• Genetic code is the sequence of nucleotides in DNA or RNA that determines the sequence of amino acids in a polypeptide chain.
• George Gamow suggested that genetic code should be a combination of 3 nucleotides to code 20 amino acids.
• H.G. Khorana developed a chemical method to synthesise RNA molecules with a defined combination of bases.
• Marshall Nirenberg’s system for protein synthesis finally helped in deducing the code.

Salient Features of Genetic Code

• The code is triplet. 61 codons code for amino acids and 3 codons do not code for any amino acids; these are called stop codons (UAG, UGA and UAA).
• Codon is unambiguous and specific. It codes for just one amino acid.
• The code is degenerate; this means that some amino acids are coded by more than one codon.
• The codon is read in mRNA in a continuous fashion; without any punctuation.
• The codon is nearly universal. AUG has a dual function. It codes for methionine amino acid and also acts as an initiator codon.