Experiments for Deciphering the Genetic Code, Contribution of Researchers

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HarGobind Khorana’s Chemical Method

HarGobind Khorana, a key figure in deciphering the genetic code, developed a chemical method to synthesize RNA molecules with defined sequences. By creating homopolymers (RNA molecules consisting of one repeated nucleotide) and copolymers (RNA molecules consisting of combinations of two or more different nucleotides), Khorana was able to study how RNA sequences correspond to amino acids. For example, Khorana synthesized homopolymers like poly-U (UUUUUUUU), where the codon "UUU" codes for the amino acid phenylalanine. He also synthesized copolymers, such as poly-UC (UCUCUCUCUC), which gave the codons "UCU" (serine) and "CUC" (leucine), providing further evidence of how combinations of RNA nucleotides code for specific amino acids. Khorana’s work was instrumental in proving that the genetic code is a triplet code, with three nucleotides (a codon) corresponding to one amino acid. This experiment was a crucial step in understanding that the genetic code is composed of triplets of nucleotides, and it helped establish the foundation for subsequent discoveries about the genetic code's structure.

Marshall Nirenberg’s Cell-Free Protein Synthesis System

Marshall Nirenberg made a groundbreaking contribution to deciphering the genetic code with his development of a cell-free protein synthesis system. Before Nirenberg’s work, scientists could not translate RNA into proteins outside of living cells. By creating a cell-free system, Nirenberg was able to use synthetic RNA molecules with known sequences to study protein synthesis in vitro. Nirenberg used RNA sequences composed of repeating nucleotides (e.g., poly-U, poly-A, and poly-C) and added them to a mixture containing the necessary components for protein synthesis. He then observed which amino acids were incorporated into the growing polypeptide chains during translation. This allowed him to identify which codons (sequences of three nucleotides) corresponded to which amino acids. For example, he found that the codon "UUU" codes for phenylalanine, while "AAA" codes for lysine. Nirenberg’s work was crucial in identifying the specific codon-amino acid pairs, and he eventually deciphered the codon table, showing the complete correspondence between codons and the amino acids they code for. This experiment provided essential proof of the triplet nature of the genetic code and played a significant role in uncovering its full structure.

Severo Ochoa’s Enzymatic Synthesis of RNA

Severo Ochoa contributed to the study of the genetic code through his work on the enzymatic synthesis of RNA. Ochoa used an enzyme called polynucleotide phosphorylase to synthesize RNA molecules without needing a DNA template. This method allowed him to create RNA molecules with specific sequences, which he could then use in various experiments. Ochoa’s technique of synthesizing RNA molecules in vitro was critical because it enabled researchers to create RNA sequences with known bases and test how those sequences were translated into proteins. By synthesizing RNA sequences that represented different codons and testing their translation, Ochoa's work helped confirm the findings of Nirenberg and Khorana. His contribution, along with that of other researchers, led to the realization that RNA serves as the template for protein synthesis, and that specific RNA sequences determine the sequence of amino acids in proteins. Ochoa’s enzymatic method also supported the hypothesis that RNA sequences are translated into proteins through the genetic code.

MCQs of Experiments for Deciphering the Genetic Code

Q1. Hargobind Khorana is known for;

1. discovery of DNA
2. discovery of DNA ligase
3. discovery of tRNA
4. discovery of genetic code

Q2. Hargobind Khorana is known for;

1. synthesis of polynucleoide phosphorylase.
2. cell - free system of protein synthesis.
3. postulation that the code should be made of three nucleotides.
4. synthesis of RNA molecule using defined combination of bases (homopolymers and copolymers).

Q3. ___________ cell-free system for protein synthesis finally helped the genetic code to be deciphered;

1. George Gamow
2. Marshal Nirenberg
3. Har Gobind Khorana
4. J.D. Watson

Answers of MCQs of Experiments for Deciphering the Genetic Code

Ans1. Discovery of genetic code, Ans2. Synthesis of RNA molecule using defined combination of bases (homopolymers and copolymers)., Ans3 . Marshal Nirenberg Physics Wallah (PW) offers NEET Online Coaching in India, designed to make quality education accessible to all aspiring medical students. With a focus on breaking down financial barriers, PW is dedicated to empowering students nationwide to excel in the NEET exam and achieve their dreams of a medical career.