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  • Nirenberg synthesized an RNA having 34 adenine residues (AAAA...) and obtained a polypeptide of 11 lysine residues. It proved that genetic code for lysine is  <div class='qna-opt

Nirenberg synthesized an RNA having 34 adenine residues (AAAA...) and obtained a polypeptide of 11 lysine residues. It proved that genetic code for lysine is

 

Option: 1

Adenine


Option: 2

AA


Option: 3

AAA


Option: 4

AAAA....A


Answers (1)

best_answer

Nirenberg and Matthei found one enzyme called polynucleotide phosphorylase that when used in a cell free system made uridine diphosphate into a poly-U- messenger RNA (mRNA). This was then used for cracking the genetic code by them, i.e, to understand which codon codes for which amino acid. They used a cell-free system in a test tube where they put together all the things they needed for protein synthesis - RNA template (poly-U-mRNA), ribosomes, nucleotides, amino acids, stabilizing agents and energy. They found phenylalanine residues being incorporated into the polypeptide as mentioned in the question. Ribosomes read the information in the mRNA and incorporate the specific amino acid. Each three letter nucleotide code is read as one codon and a specific amino acid is added. No amino acid is incorporated for the three stop codons. Similarly a 34 poly adenine mRNA ( i.e (A-A-A-A-A-A-----) sequence will encode a 11 amino acid peptide. Since 34 when divided by 3 gives 11 (approx), therefore it shows the genetic code for lysine is a triplet i.e AAA. Thus, the correct option is 3. 

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