Genetic code deciphering

What is the amino acid sequence of the fusion protein Where is the junction between /3-galactosidase and the sequence encoded by the insert (Consult the genetic code table on the inside front cover to decipher the amino acid sequence.)... 

The cell must possess the machinery necessary to translate information accurately and efficiently from the nucleotide sequence of an mRNA into the sequence of amino acids of the corresponding specific protein. Clarification of our understanding of this process, which is termed translation, awaited deciphering of the genetic code. It was realized early that mRNA molecules themselves have no affinity for amino acids and, therefore, that the translation of the information in the mRNA nucleotide sequence into the amino acid sequence of a protein requires an intermediate adapter molecule. This adapter molecule must recognize a specific nucleotide sequence on the one hand as well as a specific amino acid on the other. With such an adapter molecule, the cell can direct a specific amino acid into the proper sequential position of a protein during its synthesis as dictated by the nucleotide sequence of the specific mRNA. In fact, the functional groups of the amino acids do not themselves actually come into contact with the mRNA template. 

It is now known that each codon consists of a sequence of three nucleotides ie, it is a triplet code (see Table 38—1). The deciphering of the genetic code depended heavily on the chemical synthesis of nucleotide polymers, particularly triplets in repeated sequence. 

This revolution in our understanding of the structure of DNA inevitably stimulated questions about its function. The double-helical structure itself clearly suggested how DNA might be copied so that the information it contains can be transmitted from one generation to the next. Clarification of how the information in DNA is converted into functional proteins came with the discovery of both messenger RNA and transfer RNA and with the deciphering of the genetic code. 

In the next step, translation, the sequence of nucleotides in the newly synthesized mRNA strand is used to determine the sequence of amino acids in the protein to be synthesized. This is done by way of a genetic code, which was fully deciphered by 1966 and is shown in Figure 13.34. According to the genetic code, it takes three mRNA nucleotides—each three-nucleotide unit is called a codon—to code for a single amino acid. The mRNA nucleotide sequence AGU, for example, codes for the amino acid serine, and AAG codes for lysine. (Note from Figure 13.34 that more than one codon can call for the same amino acid.) A few codons, such as AUG and UGA, are the signals for protein synthesis to either start or stop. 

Gierasch, L. M. King, J. (1990). Protein Folding Deciphering the Second Half of the Genetic Code. American Association for the Advancement of Science, Washington, D. C. 

The rosters of those who have conducted research, or who have received NIH support over the years include the world s most illustrious scientists and physicians. Among them are 97 scientists who have won Nobel Prizes for achievements as diverse as deciphering the genetic code... 

The Code was deciphered five decades ago some colleagues are so secretive that they do not let a word about it anymore. The Genetic Code codes for proteins in 64 triplets that consist of the four bases of RNA. A group of three adjacent letters is a codon and it codes for an amino acid. In addition, three codons stand for stop signs, that is, they determine the end of a protein chain. 

Determination of Amino acid Sequence from DNA sequence. Understanding genetic codes and our ability to sequence nucleotides in a DNA segment made it possible to decipher the amino acid sequence of a protein encoded by a gene. It became customary to infer the amino acid sequences of different proteins as soon as the DNA sequence data became available in the gene bank. The primary structure of a large number of proteins deposited in the protein data bank (PDB) is obtained directly from the DNA sequence data. 

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