Word: amino
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Dates: during 1960-1969
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...They Did It. The Rockefeller researchers, Drs. Robert B. Merrifield and Bernd Gutte, began their experiment with a tiny bead of plastic, onto which they hooked a 124-link chain of amino acids. There are 20 different amino acids, and, because all proteins, including enzymes, are made of amino-acid chains, the acids have been recognized for many years as the "building blocks of life." The exact sequence and identity of successive acids in the ribonuclease chain were recently established, and the Rockefeller team's job was to link them, one at a time. The painstaking process involved...
...chemical compounds called nucleotides. There are only four different kinds of nucleotides in DNA, but the order in which they appear along the length of the helix varies considerably, suggesting that they are arranged in a coded sequence. To be able to call up one of the 20 different amino acids using only four nucleotide "letters," scientists decided, each genetic code "word" has to be three letters long. But how to break the code...
...Nirenberg, then an obscure young scientist at the National Institutes of Health, provided the biological Rosetta stone. After synthesizing a single helix with half-stairs that were the equivalent of only one of DNA's nucleotides-adenine (A)-he added it to a solution containing all 20 amino acids. Only one protein was produced in the solution. It consisted entirely of a chain of amino-acid molecules called phenylalanine. Thus, Nirenberg concluded, a three-letter code word made up of adenine nucleotides (AAA) was nature's instruction to the cell to use phenylalanine in building a protein...
Punched-Tape Message. Nirenberg refined his technique and began to match other three-letter combinations of nucleotides with particular amino acids. The task was also taken up independently by Khorana at the University of Wisconsin. Other scientists pitched in, and by 1965 the genetic code had been largely deciphered. Khorana was also able to determine that each of the three-letter words is always read separately and does not share any of its letters with another word. The words are read off continuously along a strand of DNA, much as a punched-tape message is read by a teletype machine...
...Cornell, Holley studied both the genetic code and its function in building proteins by analyzing "transfer RNA," a form of ribonucleic acid. RNA collects amino acids floating in the cell and, like a tug towing a barge, pulls them to an assembly site where, in the sequence dictated by the master DNA molecule, they are combined into the appropriate protein. Holley worked out the complete structure of a transfer RNA molecule, demonstrating how it attaches to a particular amino acid and brings it to the growing protein chain at the proper time and place...