Deoxyribonucleic Acid

Literature References: Polynucleotide; essential component of chromosomes in cell nuclei. In its role as the carrier of genetic information, DNA must have two functions: be exactly reproducible in order to transmit its genetic information to future generations; contain information, in chemical code, to direct the development of the cell according to its inheritance. Reviews of biological function: Hotchkiss in The Nucleic Acids vol. 2, E. Chargaff, J. N. Davidson, Eds. (Academic Press, New York, 1955) pp 435-473; Crick, Nature 227, 561 (1970); J. N. Davidson, The Biochemistry of Nucleic Acids (Academic Press, New York, 7th ed., 1972) pp 6-28. The purine and pyrimidine bases of the nucleosides are primarily adenine, guanine, cytosine and thymine; the sugar is D-2-deoxyribose, q.q.v. The nucleosides are linked together by phosphates in diester linkage from the 3¢-hydroxyl of one sugar to the 5¢-hydroxyl of the next. The repeating sugar-phosphate linkage forms the backbone of the single polynucleotide strand which is the primary structure of DNA. Chemical analyses of DNA from different species show that the purine content is equal to the pyrimidine content; adenine content equal to thymine; guanine equal to cytosine: Chargaff, Experientia 6, 201 (1950); idem, Fed. Proc. 10, 654 (1951). In the Watson-Crick model of its secondary structure (based on chemical analysis and x-ray studies), DNA consists of two polynucleotide chains forming right-handed helices coiled around the same axis with the sequence of atoms in the two sugar-phosphate backbones running in opposite direction. Two major families of right-handed helix were proposed. A-DNA and B-DNA, each having its own intrinsic restrictions on chain-folding and structure. B-DNA is believed to be the predominant form in biological systems. The purine and pyrimidine bases are inside the helical structure formed by the sugar phosphate backbones; those on one chain form hydrogen bonds to those on the other. Adenine in one chain is always bonded to thymine in the complementary chain by hydrogen bonds; similarly guanine is bonded to cytosine. The linear sequence of bases in one strand completely determines the sequence in the complementary strand. Thus each strand can serve as a template for the replication of the original DNA molecule: Watson, Crick, Nature 171, 737, 964 (1953). X-ray studies: Wilkins et al., ibid. 738; Marvin et al., J. Mol. Biol. 3, 547 (1961); Fuller et al., ibid. 12, 60 (1965). DNA also acts as a template in the formation of ribonucleic acids, q.v., which play a fundamental role in the synthesis of proteins in the cell. Another form of DNA, termed Z-DNA, is also known. Its structure is an antiparallel double helix with Watson-Crick base pairing, but it is a left-handed helix with the ribose-phosphate backbone following a zig-zag course. Molecular structure, atomic resolution x-ray crystallographic analysis: A. H.-J. Wang et al., Nature 282, 680 (1979). First identification of Z-DNA in material of biological origin: A. Nordheim et al., ibid. 294, 417 (1981). Studies of B- and Z-DNA: D. J. Patel et al., Proc. Natl. Acad. Sci. USA 79, 1413 (1982). Comparison of A-, B-, and Z-DNA: R. E. Dickerson et al., Science 216, 475 (1982). Demonstration of Z-DNA immunoreactivity in rat tissues: G. Morgenegg et al., Nature 309, 540 (1983).