Word: proteins
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Dates: during 1970-1979
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Scientists suspected that DNA had a helper, a single-stranded chemical first cousin called ribonucleic acid (RNA). Most of the cell's RNA is found in ribosomes. These are globular bodies in the material outside the cell's nucleus that seem to be highly active centers of protein synthesis. But if this ribosomal RNA played a role in protein making, how did it obtain and execute the instructions from the master molecule DNA inside the nucleus...
...Pasteur Institute. Called messenger RNA, it provided the missing piece in the molecular puzzle. It was formed on an uncoiled strip of DNA in the nucleus, imprinted with the particular "message" encoded in that portion?or gene?of the staircase, and then sent off with these instructions to the protein-making ribosomes...
...CRICK'S team at Cambridge proved Gamow's ingenious "triplet" theory. They demonstrated that RNA formed from only one or two base units could not effect the manufacture of proteins. But when they added a third base unit, protein formation began immediately. It remained, however, for an unknown young biochemist named Marshall Nirenberg, at the National Institutes of Health, to crack the code itself. That same year Nirenberg had succeeded in building up short, synthetic strands of RNA out of only one type of base. Invariably, this artificial RNA induced the manufacture of chains of proteins consisting of only...
...this clue as their Rosetta stone, Nirenberg and other researchers eventually found one or more three-letter code words, or codons, that could call up every single amino acid?plus other words that acted as punctuation, marking the start or completion of a message ordering the production of a protein. Even more remarkable, they learned that the code was universal: the same four letters, taken three at a time to form a single genetic word, code the same amino acids in all living things. Thus by the mid-1960s, scientists finally understood how DNA passes on genetic information with exquisite...
That process, shown in the accompanying color chart, was summarized by Crick in a series of rules that became known as the Central Dogma. Most scientists interpreted the key rule of that dogma to be that genetic information flowed in one direction: from DNA to RNA to protein. To the surprise of many molecular biologists, however, it has recently been shown that part of the process can sometimes be reversed. This finding, in the opinion of molecular biologists like Columbia's Sol Spiegelman, may offer an important clue to the workings of cancer cells (see box, page...