Question
Cracking of genetic code.
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Answer
- M. Nirenberg and Matthaei synthesized artificial poly-U m-RNA.
- Using this synthetic poly-U m-RNA and cell free system of protein synthesis, a small polypeptide consisting of only amino acid phenylalanine was obtained.
- It suggested that UUU codes for phenylalanine.
- Dr. Har Gobind Khorana devised a technique for synthesis of artificial m-RNA with repeated sequences of known nucleotides.
- He synthesized artificial RNA consisting of known repeated sequences of two or three nucleotides. E.g. CUC, UCU, CUC, UCU, by using synthetic DNA.
- This resulted in formation of polypeptide chain consisting of alternate amino acids leucine and serine.
- Synthetic RNA consisting of CUA, CUA, CUA, CUA repeats gave polypeptide chain with only one amino acid – leucine.
- Severo Ochoa established that the enzyme (polynucleotide phosphorylase) also helps in polymerizing RNA of defined sequences in a template-independent manner (i.e. enzymatic synthesis of RNA).
- Thus all the 64 codons in the dictionary of genetic code were deciphered.
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