Nucleic acids, chemical constitution

A wide variety of bases, nucleosides and nucleotides have been separated using porous layer bead ion exchangers. A representative chromatogram of the separation of ribonucleoside mono-phosphoric acids from the work of Smukler ( ) is shown in Figure 4. Recently, ion exchangers chemically bonded to small particle diameter (> 10 ym) silica have been successfully applied to the separation of nucleic acid constitutents (37). The rapid separations using such supports undoubtedly mean that they will find increasing use in the future. 

This subject has been of continuing interest for several reasons. First, the present concepts of the chemical constitution of such important biopolymers as cellulose, amylose, and chitin can be confirmed by their adequate chemical synthesis. Second, synthetic polysaccharides of defined structure can be used to study the action pattern of enzymes, the induction and reaction of antibodies, and the effect of structure on biological activity in the interaction of proteins, nucleic acids, and lipides with polyhydroxylic macromolecules. Third, it is anticipated that synthetic polysaccharides of known structure and molecular size will provide ideal systems for the correlation of chemical and physical properties with chemical constitution and macromolecular conformation. Finally, synthetic polysaccharides and their derivatives should furnish a large variety of potentially useful materials whose properties can be widely varied these substances may find new applications in biology, medicine, and industry. 

From the beads-on-a-string linear topology, research moved to the mapping of genes in a chromosome, and later to the discovery that genes were nucleic acids. Their chemical constitution was then determined, first topologically according to the classic structural theory procedures by Todd, and finally in the three-dimensional structural pattern (3D) of the DNA double helix proposed by Watson and Crick in 1953. 

The three covalent biomacromolecules share some similarities in their global structures but differ in their cellnlar functions and structural details. DNA is the carrier of genetic information, which mnst be faithfully duplicated and selectively transcribed so that each cell can synthesize the proteins it needs. RNA functions mainly in the transcription and translation of this information. In order that the nucleic acids may convey genetic information, a pattern or code must be incorporated in their chemical structure. Purine and pyrimidine bases are arranged in a definite sequence and this sequence constitutes the genetic code. 

If some of the physico-chemical properties of nucleic acids pose many challenges to their analysis by MALDI-TOF, then some others afford intrinsic advantages as compared to proteins /peptides and other biomolecules. For instance, their primary structure is much more homogeneous than that of proteins, consisting of only four relatively similar building blocks. Because of this structural simplicity and homogeneity, relative and even absolute (with an internal standard) quantification can be readily accomplished and this constitutes the basis for a number of assays (as discussed below). The remainder of this chapter is mostly devoted to descriptions of the different assays that have been developed for the analysis of NAs, under the somewhat restrictive boundary conditions of UV-MALDI-TOF-MS. 

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