Q.Which of the following Codon codes for methionine ?

The Genetic Code and Its Discovery

The genetic code is the set of rules by which the base sequence of mRNA is translated into the amino-acid sequence of a protein. It is read in triplets (codons) of three nucleotides; with four bases there are $4^3 = 64$ codons specifying 20 amino acids plus start/stop signals. The code is degenerate, non-overlapping, comma-less, nearly universal and has a defined start (AUG) and stop codons.

Its elucidation involved several scientists, frequently matched in examinations:

• George Gamow — proposed that the code is made of three nucleotides.
• Marshall Nirenberg (with Matthaei) — cracked the code using a cell-free system for protein synthesis.
• Har Gobind Khorana — chemically synthesised RNA with defined repeating sequences to assign codons.
• Severo Ochoa — discovered polynucleotide phosphorylase, the enzyme used to make synthetic RNA.

Pairing each worker with their specific contribution to the genetic code is the usual requirement. …