Word: helix
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Dates: during 1970-1979
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...architecture of their precisely constructed double helix emerged the secret of DNA's awesome powers. The banisters of the staircase were fashioned of long links of sugars and phosphates; the steps between them were made of pairs of chemicals called bases, weakly joined at the center by hydrogen atoms. Only four different bases were used?adenine (A), thymine (T), cytosine (C) and guanine (G). But their sequence could vary so widely along the length of the staircase that they made up an almost limitless information-storage system, like the memory bank of a computer. In addition, because the bases were...
...base pairs breaking apart at their hydrogen bonds. Then by drawing on the free-floating material surrounding them in the nucleus of the cell, the two separated strands link up with complementary base-and-strand units along their entire length, forming two exact copies of the original double helix. Thus DNA faithfully passes its genetic information on to new cells and to future generations...
...demanded proof that the molecule actually replicated itself. That proof was quick to come. By 1956, Arthur Kornberg, then at Washington University in St. Louis, discovered an enzyme, or natural chemical catalyst (which he named "DNA polymerase") that was apparently critical to some of the activities of the double helix. Once he obtained enough of the enzyme, he placed it in a test-tube brew with a bit of natural DNA, one of whose strands was incomplete, the four bases (A, T, C, G) and a few other off-the-shelf chemicals. True to his expectations?and the Watson-Crick...
...distinctive proteins that make up the cells of the eye, for example, differ from those of the kidneys or muscles. Despite their variety, however, all proteins are built from some of only 20 smaller and simpler molecules, called amino acids. How then, scientists asked themselves, did the isolated double helix, locked in the nucleus of the cell, direct the assembly of amino acids into protein in other parts of the cell...
...formed viruses to infect other cells. Dr. Howard Temin of the University of Wisconsin has shown that some tumor viruses behave differently. They reverse the normal order of genetic transmission, and with the aid of a recently discovered enzyme, use their RNA messenger molecules to produce DNA, the double-helix master molecule. In a way not yet understood, this triggers the cellular genetic machinery to order cell division, causing the cancerous growth that is then perpetuated in succeeding cell generations...