Match List-I with List-II.
| List-I | List-II |
| (A) Erwin Chargaff | (I) Cell-free system for protein synthesis that finally helped the code to be deciphered |
| (B) Har Gobind Khorana | (II) Observed that in double stranded DNA the ratios between adenine and thymine and between guanine and cytosine are constant and equal one |
| (C) Marshall Nirenberg | (III) Enzyme (polynucleotide phosphorylase) used for polymerising RNA with defined sequences in a template independent manner |
| (D) Severo Ochoa | (IV) Chemical method for synthesising RNA molecules with defined combinations of bases |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A-II, B-IV, C-I, D-III
(A) Erwin Chargaff — this matches (II) Observed that in double stranded DNA the ratios between adenine and thymine and between guanine and cytosine are constant and equal one. This base ratio (A = T, G = C) supported the base pairing that Watson and Crick put into their double helix model.
(B) Har Gobind Khorana — this matches (IV) Chemical method for synthesising RNA molecules with defined combinations of bases. Khorana made RNA molecules of known sequence (homopolymers and copolymers) by chemical means, which helped prove that the codon is a triplet.
(C) Marshall Nirenberg — this matches (I) Cell-free system for protein synthesis that finally helped the code to be deciphered. In a cell-free system, a known RNA could be translated outside the cell, so the amino acid made from each codon could be found.
(D) Severo Ochoa — this matches (III) Enzyme (polynucleotide phosphorylase) used for polymerising RNA with defined sequences in a template independent manner. This enzyme joins ribonucleotides without any DNA template, so it gave an enzymatic way to make RNA of chosen sequence.
NCERT Extract:
Structure of Polynucleotide Chain – “… It was only in 1953 that James Watson and Francis Crick, based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin, proposed a very simple but famous Double Helix model for the structure of DNA. One of the hallmarks of their proposition was base pairing between the two strands of polynucleotide chains. However, this proposition was also based on the observation of Erwin Chargaff that for a double stranded DNA, the ratios between Adenine and Thymine and Guanine and Cytosine are constant and equals one.”
Genetic Code – “… Providing proof that the codon was a triplet, was a more daunting task. The chemical method developed by Har Gobind Khorana was instrumental in synthesising RNA molecules with defined combinations of bases (homopolymers and copolymers). Marshall Nirenberg’s cell-free system for protein synthesis finally helped the code to be deciphered. Severo Ochoa enzyme (polynucleotide phosphorylase) was also helpful in polymerising RNA with defined sequences in a template independent manner (enzymatic synthesis of RNA).”