Word: helix
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Dates: during 1960-1969
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...recognized as the basic unit of heredity, it has been only 26 years since molecular biologists learned that the gene is actually composed of deoxyribonucleic acid (DNA) a complex molecule that forms the chromosomes in every living cell. The DNA molecule is shaped like a spiral staircase-a double helix connected by steps, or links. Each of the thousands of links consists of a pair of mutually attracting chemical bases. Although only four different kinds of such bases are found in DNA, they can be arranged along the helix in an enormous variety of sequences. Each of these sequences contains...
...lies the key to the elegant experiment reported last week in Nature. Once the two strains of virus had finished raiding the bacteria, the experimenters dissolved their protein sheaths, exposing their raw DNA molecules (Step 1 in diagram). Next, the scientists heated the dissimilar DNA molecules, causing each double helix to unwind and separate into one lighter and one heavier strand. Taking only the heavier strand from each virus, the researchers placed them in the same test tube, reheated them and then cooled them slowly, a process that causes two chemically complementary strands of DNA to combine in a double...
These and other discoveries led scientists to concentrate on the structure of the DNA molecule. The finding in 1953 by James Watson and Francis Crick that the typical DNA molecule consists of a double helix enabled scientists to reduce to relatively simple chemical terms the process by which inherited traits are passed on. But it was the contributions of Delbruck, Luria and Hershey that, in the words of the Nobel committee "set the solid foundation on which modern molecular biology rests...
...trial-and-error methods, Researchers James Watson and Francis Crick determined that the heredity-transmitting DNA molecule is shaped like a spiral staircase. Al though they had no way of taking a firsthand look at their discovery, they managed to deduce a detailed description of the now famous "double helix" that paved the way for the new science of molecular biology and won them the Nobel Prize. For all the work that has been done in the field since Watson and Crick made their pioneering studies in 1953, no one had been able to display any hard and fast visual...
...structure. The resulting pictures, which Biophysicist Griffith painstakingly developed himself to bring out maximum detail, show a blurred image that has been magnified 7,300,000 times. Fuzzy as they are, the pictures are clear enough to reveal two DNA strands that are coiled and intertwined in a double helix-just as Watson and Crick predicted nearly 16 years earlier...