Explain the contributions of the following scientists:
$1.$ George Gamow
$2.$ Marshall Nirenberg

(N/A) George Gamow was a physicist who argued that since there are only $4$ bases and $20$ amino acids to be coded,the code must be a combination of bases. He suggested that in order to code for all $20$ amino acids,the code should be made up of three nucleotides (triplet code).
Marshall Nirenberg was a biochemist who helped crack the genetic code. He developed a cell-free system for protein synthesis and used synthetic $RNA$ (poly-$U$) to demonstrate that the triplet $UUU$ codes for the amino acid phenylalanine.