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JAMA. 1961;175(5):396-397. doi:10.1001/jama.1961.03040050052016.
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At the focal point of biological phenomena lies the question how information is transferred by genetic means from one generation of cells or organisms to the next. With the exception of some viruses, the molecular carrier of the hereditary code is generally recognized to be the polynucleotide deoxyribonucleic acid (DNA). DNA, with the exception of that derived from a particular virus, is a double-stranded helical molecule composed of purine and pyrimidine nucleotides held together by phosphodiester bonds. The two intertwined helices are held in contact with one another by hydrogen bonding between the adenine residues on one strand and the thymine residues on the other; the guanine of one and the cytosine of the other.1 Since the molecular weight of DNA is thought to be in the neighborhood of 10 million, it is composed of about 300,000 nucleotide units. The information carried on one strand is necessarily duplicated on


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