Chapter 53 - 1979 Genetic Code

Abstract

The genetic code is universal. The genetic code is the set of biochemical rules governing how genetic information encoded in nucleic acids is converted into polypeptides (proteins). Basically, in a translational process that takes place on a cell’s ribosomes, successive triplets of nucleotides in a nucleic acid specify precisely which amino acids are to be added to a growing polypeptide chain. For example, the triplet AAA in an RNA sequence normally specifies the incorporation of a lysine, whereas the triplet CGC specifies arginine. With four different types of nucleotides (A, T, C, and G), a total of (4)3=64 different nucleotide triplets exist. The genetic code typically is presented as a table showing which amino acid is specified by each such codon. The genetic code was painstakingly deciphered in the early 1960s (an accomplishment for which Har Khorana, Robert Holley, and Marshall Nirenberg later shared a Nobel Prize), and for the next two decades it was assumed to apply universally to all forms of life on Earth.