Question

Hargobind Khorana was awarded Nobel Prize for
(a)Deciphering genetic code
(b)Artificial gene synthesis
(c)Nucleotide sequence of tRNA
(d)Discovery of transposons

Answer 1

Developed a chemical method for synthesis of RNA with defined combinations of nucleotides in vitro
Marshall Nirenberg, Hargobind Khorana and Robert W. Holley were jointly awarded Nobel Prize in Medicine in 1968 for elucidating how the four bases - A, U, G, and C, determine the sequence of the 20 different amino acids during protein synthesis.

Complete step by step answer:
In 1961, Nirenberg described first that base is a triplet, a set of three nucleotides that make up a codon. The triplet code for one of the twenty amino acids used to build proteins.
-Nirenberg along with German scientist Johann Matthaei conducted a series of test-tube experiments.
-They added RNA chains containing only one of the 4 bases of RNA - A, G, U, and C – along with radioactively tagged amino acids to a cell-free system.
-They took 20 test tubes, each containing a synthetic poly(U) mRNA, GTP, ATP, E. coli extract and a mixture of the 19 non-labelled amino acids and one different radioactively labelled amino acid.
-The poly(U) mRNA has many successive UUU triplets and out of 20 tubes, one tube had the production of a radioactive polypeptide made up entirely of single amino acid, phenylalanine.
-Based on this result, these researchers concluded the triplet codon UUU encodes phenylalanine.
-Later Khorana developed a method for chemical synthesis of RNA with known combinations of bases in a template-independent manner. The first of these nucleic acids was made up of a repeating sequence of the two bases- U and C, which, after translation, gave an amino acid chain made up of serine and leucine.
- The use of artificially synthesised mRNA for in vitro synthesis of polypeptides helped ascertain the rest of the genetic code.

Hence the correct answer is option(B)

Note: Severo Ochoa, a biochemist and molecular biologist, along with the American biochemist, Arthur Kornberg received the 1959 Nobel Prize for Physiology or Medicine for the discovery of an enzyme called polynucleotide phosphorylase in bacteria that enabled him to synthesise ribonucleic acid (RNA).