AP BIOLOGY

Detailed explanation-1: -Marshall Nirenberg, Har Gobind Khorana, and their colleagues, were the first to determine the genetic code and show how the nucleic acid bases, with their alphabet made up of A, U, G, and C, determine the sequence of the 20 different amino acids during protein synthesis.

Detailed explanation-2: -In 1968 Nirenberg won the Nobel Prize in Physiology or Medicine for his seminal work on the genetic code. He shared the award with Har Gobind Khorana (University of Wisconsin), who mastered the synthesis of nucleic acids, and Robert Holley (Cornell University), who discovered the chemical structure of transfer-RNA.

Detailed explanation-3: -Watson and Crick were the first to realize that the seemingly random sequence of the four bases in DNA formed a code which specified the order of the twenty amino acids that make up most proteins.

Detailed explanation-4: -In 1961, Francis Crick, Sydney Brenner, Leslie Barnett, and Richard Watts-Tobin first demonstrated the three bases of DNA code for one amino acid [7].

Detailed explanation-5: -Nirenberg and Matthaei created a synthetic RNA molecule outside the bacterium and introduced this RNA to E. coli. They found that their synthetic RNA specified that phenylalanine, an amino acid, be added to the end of a growing strand of linked amino acids, the precursor to proteins.