The Structure Of Nucleic Acid Polymers

A firm knowledge of the structure of DNA is of crucial importance. The gross dimensions of DNA were found by light-scattering or viscosity measurements, which indicate that DNA is a long, thin, relatively rigid structure whose molecular weight is ~6 X 106 and density is 1.6 to 1.75 g/cm3. Chemical evidence indicates that the phosphate (PO4 ) groups are very reactive, but the amino (— NH2) and CO groups are not readily titratable. The analysis of Wyatt and Chargaff (13) indicated that the ratio of thymine to adenine is unity, and the ratio of cytosine or its derivatives to guanine is also about unity. The absorption of polarized infrared light indicates that the -NH2 and -C = O groups of the bases are oriented perpendicular to the molecular axis.

Table 3. Bases Involved in Nucleic Acids

Pyrimidines

Cytosine

NH2 CH

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