CHEMICAL ARCHITECTURE OF THE CENTRAL NERVOUS SYSTEM 



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are the liponucleoproteins, the phosphoproteins and 

 the proteolipids. The first two account for the majority 

 of protein-bound phosphorus in brain (141) and 

 exhibit a high rate of phosphate turnover (24, 47, 

 98, 215). Proteolipids are complexes which are 

 rather peculiar to brain and occur primarily in the 

 white matter (72). Their general constitution is 

 indicated in table 3. Despite the high protein content, 

 these compounds behave chemically like lipids. 

 Much of the lipid is composed of phosphatides, and 

 the demonstration of phosphatidopeptides in white 

 matter (70) suggests that these may represent inter- 

 mediate or subunits of some proteolipids. These 

 phosphatidopeptides consist of diphosphoinositide, 

 sphinogosine, or both, plus fatty acids and short 

 peptide chains, averaging seven amino acids in 

 length. 



Nucleoprotcins, representing aggregations of nucleic 

 acids with proteins, are of great importance to the 

 cell. Essentially all of the desoxyribonucleic acid 

 (DNA) proteins are in the cell nuclei and are con- 

 cerned with specific nuclear functions such as genetic 

 constitution. Because of this, the amount of DNA per 

 nucleus (or per cell) is constant for all except germinal 

 tissues of a given organism, and this fact has been 

 utilized to permit a simple determination of the total 

 cell population of cerebral tissue samples (9c), [91). 

 The DNA content per nucleus of cerebral tissues was 

 found by Heller & Elliott (99) to be 6.5 to 7.1 pgm 

 (io" 1 ' 2 gm) for cat, dog and man. The ribonucleic 

 acid (RNA) proteins are present in the nucleolus 

 and especially in cytoplasmic Nissl substance. They 

 are important in protein synthesis and represent the 

 principal sites of amino acid incorporation into 

 peptide and protein structure (82, 89, 115, 121, 140, 

 184, 208). The mechanisms whereby this is ac- 

 complished are not well understood, but it is thought 

 that the protein moiety may provide the enzymes and 

 the nucleic acids a sort of template for the process 

 (11, 48, 184I. 



The principal units composing the nucleic acids 

 are illustrated in figure 4. The purine and pyrimidine 

 bases are joined to ribose, or deoxyribose, at the 

 point indicated by .V to form nucleosides which, 

 when phosphorylated, are termed nucleotides. The 

 phosphate addition is usually at the 5'-position on 

 the pentose chain, as shown, but may attach at 

 positions 2' or 3' (indicated as .1 and B respectively 

 in the figure). DNA differs from RNA in utilizing 

 deoxyribose and containing the pyrimidine thymine 

 instead of uracil; otherwise it is similar to RNA. 

 Nucleotides are aggregated by means of phosphate- 



fig. 4. Structural formulas of the purines and pyrimidines 

 present in nucleotides. The addition of a pentose molecule to 

 these bases at point X constitutes a nucleoside, as indicated at 

 the bottom for adenine Addition of a phosphate ijroup to the 

 pentose, usually in the 5' position, as shown at the bottom, 

 constitutes a nucleotide. Additions of further phosphates at A" 

 [bottom formula) result in nucleotide polyphosphates, such as 

 ATP (0,71. 



pentose bridges (at point .1 or B) to form nucleic 

 acids. A schematic radical is shown in figure 5. 

 Originally it was thought that nucleic acids were 

 composed of multiples of such tetranucleotide (or 

 pentanucleotide) radicals, but present evidence 

 indicates that the individual nucleotides are 'ran- 

 domly' distributed through the molecule. An indication 

 of this is found in the analysis of relative proportions 

 of nucleotides isolated from cat brain [see legend to 

 fig. 5 (47)]. Nucleic acid molecules appear to have 

 the form of double-stranded alpha-helices with a 

 purine of one strand paired with a pyrimidine of the 

 other by hydrogen bonds (184). The pairing is 

 generally adenine with uracil (or thymine) and 

 cytosine with guanine. Such a structure may be 

 visualized as a spiral staircase in which the purine- 

 pyrimidine pairs represent the stair treads and the 



