Molecular Biology: The Genetic Code

By: Bijay Dhungel , MSc

At the heart of molecular biology lies the notion of “information”. This information is transferred from the language of 4 letters of DNA (A,T,C,G) to the language of 20 amino acids in the proteins. The genetic code is a set of rules by which this flow of information happens. To be more specific, the code maps tri-nucleotide sequences with a single amino acid i.e. a specific sequence of 3 consecutive bases in DNA code for a particular amino acid. There are 4 bases in DNA thus the possible combinations of 3 consecutive bases (by permutation) is 43 i.e. 64. These triplet combinations are called codons. Out of the 64 possible codons, 61 encode for one of the 20 amino acids used for protein synthesis.

To bring this concept in the picture of the central dogma, it should be understood that DNA acts as a template for the synthesis of a complementary messenger RNA (mRNA) which is transported to the cytoplasm. At the cytoplasm, it is used by the ribosomes to produce protein. The ribosome decodes the mRNA and start polymerizing amino acids, the sequence of which is determined by the triplet codon in the mRNA.

Thus, the sequence of bases in the DNA determines the sequence of amino acids in the newly synthesized polypeptide chain. This sequence of amino acids determines the final structure of the protein which in turn determines its biological function.

Further Reading

  1. Web address   http://www.youtube.com/watch?v=q6PP-C4udkA
  2. Web address   http://www.youtube.com/watch?v=yqESR7E4b_8
  3. Web address   http://www.youtube.com/watch?v=YxLdBNAxqKg