We have seen that proteins, in their enormous variety, can play a host of roles in the cell, both structural and functional. Each protein accomplishes this by having a unique amino acid sequence, which determines its secondary, tertiary, and qua ternary structures. The information that dictates these sequences must somehow be stored in the cell, expressed in proteins, and transmitted through generations of cells and organisms. These vital functions are provided by biopolymers called nucleic acids, or polynucleotides, of which there are two kinds: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
In Chapter 3 we briefly described Johannes Miescher’s pioneering investigations of the cell nucleus. The substance he recovered had an unusually high phosphorus content—about 2.5%. Since proteins contain very little phosphorus—usually 1% or less—this was clearly something very different. Indeed, it was so unusual that Felix Hoppe-Seyler, Miescher’s research director, insisted on repeating the experiments himself before he would allow publication. Miescher then moved to Basel, Switzerland, and used salmon sperm as a source. A combination of acid and alkali treatments produced two fractions: one was a basic, protein-like substance, the other acidic and rich in phosphorus. The latter was termed “Nukleinsäure” (nucleic acid) and must have been close to what we recognize as DNA, for it had a phosphorus content of 9.6%, close to the currently recognized value of 9.5%. Similar preparations were obtained from nuclei of goose erythrocytes and other tissues. For some time, there was confusion between nucleic acid and chromatin, the nucleic acid-protein complex found in most cell nuclei, but by about 1890 the current distinction was clear.
This chapter will be devoted to describing these nucleic acids, their structures and possible conformations, and the multiple ways in which they can store and transmit information in the cell.
