ABSTRACT
This chapter examines the cause of the amino acid replacement. Even before the characterization of sickle cell hemoglobin and the discovery of its altered amino acid composition, it had been realized that there was a distinct relationship of genes and proteins. Every transfer ribonucleic acid (tRNA) carries an amino acid consistent with the anticodon in the molecule. The genetic code in many mitochondria is different from the universal scheme in that UGA is not a stop codon but instead encodes the amino acid tryptophan. The codon UGA is typically a stop word during the production of proteins, but when it is in a specific sequence context, it will be recognized by a specific tRNA. By the mid-1960s, the meanings of all of the codons of the genetic code had been elucidated. In 1968 Marshall Nirenberg and Gobind Khorana were awarded the Nobel Prize in Physiology or Medicine for their work on the code.
