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The Nirenberg and Leder experiment was a scientific experiment performed in 1964 by Marshall W. Nirenberg and Philip Leder. The experiment elucidated the triplet nature of the genetic code and allowed the remaining ambiguous codons in the genetic code to be deciphered. In this experiment, using a ribosome binding assay, various combinations of mRNA were passed through a filter which contained ribosomes. Unique triplets promoted the binding of specific tRNAs to the ribosome. By associating the tRNA with its specific amino acid, it was possible to determine the triplet mRNA sequence that coded for each amino acid. ==Background== Oswald.Avery discovered that the substance responsible for producing inheritable change in the disease-causing bacteria was neither a protein nor a lipid, rather deoxyribonucleic acid (DNA). He and his colleagues Colin MacLeod and Maclyn McCarty suggested that DNA was responsible for transferring genetic information. Later, Erwin Chargaff discovered that the makeup of DNA differs from one species to another. These experiments helped pave the way for the discovery of the structure of DNA. In 1953, with the help of Maurice Wilkins and Rosalind Franklin’s X-ray crystallography, James Watson and Francis Crick proposed DNA is structured as a double helix. In the 1960s, one main DNA mystery scientists needed to figure out was in translation how many bases would be in each code word, or codon. Scientists knew there were a total of four bases (guanine, cytosine, adenine, and thymine). They also knew that were 20 known amino acids. George Gamow suggested that the genetic code was made of three nucleotides per amino acid. He reasoned that because there are 20 amino acids and only four bases, the coding units could not be single (4 combinations) or pairs (only 16 combinations). Rather, he thought triplets (64 possible combinations) were the coding unit of the genetic code. However, he proposed that the triplets were overlapping and non-degenerate.〔 〕 Seymour Benzer in the late 1950s had developed an assay using phage mutations which provided the first detailed linearly structured map of a genetic region. Crick felt he could use mutagenesis and genetic recombination phage to further delineate the nature of the genetic code. In the Crick, Brenner et al. experiment,using these phages, the triplet nature of the genetic code was confirmed. They used frameshift mutations and a process called reversions, to add and delete various numbers of nucleotides. When a nucleotide triplet was added to or deleted from the DNA sequence, the encoded protein was minimally affected. Thus, they concluded that the genetic code is a triplet code because it did not cause a frameshift in the reading frame. They correctly concluded that the code is degenerate, that triplets are not overlapping, and that each nucleotide sequence is read from a specific starting point. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nirenberg and Leder experiment」の詳細全文を読む スポンサード リンク
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