Marshall Nirenberg is responsible for the synthesis of protein in a cell-free system. He was an American biochemist who shared the Nobel Prize in Physiology or Medicine in 1968 for his work on deciphering the genetic code.

Nirenberg's Experiment
Nirenberg and his colleagues conducted an experiment in which they synthesized RNA molecules that contained only a single nucleotide. They then added these RNA molecules to a cell-free system containing ribosomes, tRNAs, and all the other components necessary for protein synthesis. They found that the ribosomes could bind to the RNA molecules and incorporate the corresponding amino acid into a growing protein chain.

Deciphering the Genetic Code
Nirenberg's next breakthrough was deciphering the genetic code, which specifies the sequence of amino acids in a protein. He and his colleagues used artificial RNA molecules to determine which codons (three-nucleotide sequences) corresponded to each of the 20 amino acids. This work required a great deal of careful experimentation, as there are 64 possible codons and only 20 amino acids.

Significance of the Discovery
Nirenberg's work was significant because it demonstrated that it was possible to synthesize proteins in a cell-free system, without the need for living cells. This opened up new avenues of research in biochemistry and molecular biology, as researchers could now study the process of protein synthesis in a controlled environment.

Conclusion
Marshall Nirenberg's discovery of protein synthesis in a cell-free system was a major breakthrough in biochemistry and molecular biology. His work laid the foundation for further research into the genetic code and the mechanisms of protein synthesis.