Amino acids tRNA and

After the discovery of three-letter codons, researchers were anxious to answer the next question Which triplets of bases (codons) code for which amino acids In 1961, Marshall Nirenberg and his coworkers at the National Institutes of Health (NIH) in Bethesda, Maryland, attempted to break the code in a very ingenious way. They made a synthetic molecule of mRNA consisting of uracil bases only. Thus, this mRNA contained only one codon, the triplet UUU. They incubated this synthetic mRNA with ribosomes, amino acids, tRNAs, and the appropriate enzymes for protein synthesis. The exciting result of this experiment was that a polypeptide that consisted only of phenylalanine was synthesized. Thus, the first word of the genetic code had been deciphered UUU phenylalanine. 

The next question is. Which of the 64 triplets codes for which amino acid In 1961, Marshall Nirenberg provided a simple experimental approach to the problem, based on the observation that synthetic polynucleotides direct polypeptide synthesis in much the same manner as do natural mRNAs. Nirenberg found that when ribosomes, amino acids, tRNAs, and appropriate protein synthesizing enzymes were incubated in vitro. 

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