Word: dna
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Dates: during 1960-1969
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...Genetic code of the DNA molecule is broken by Marshall Nirenberg and J. Heinrich Matthaei...
Viral Assistance. Although the gene has long been 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...
...answer such questions, a Harvard team led by Jonathan Beckwith, 33, turned to the virus, which consists simply of a single DNA molecule sheathed in a thin coating of protein. Most viruses multiply by entering a living cell, taking control of it and then ordering it to produce carbon copies of the invading virus. Eventually the cell bursts, releasing a host of new viruses. Some strains of invading viruses, however, incorporate several of the cell's genes into their own DNA molecule before they depart. There are two different viruses, the Harvard researchers knew, that invade an intestinal bacteria...
Stray Tails. Therein 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...
...treating the DNA with a special enzyme that dissolves single-stranded DNA but does not effect double strands, the three researchers were able to separate the bacteria's lactose gene from the virus...