NUCLEOTIDES I27 



Co. A in acyl group transfer). The recently discovered 

 nucleotide, uridine-diphosphate-glucose, is a co-factor in 

 the enzymic conversion of galactose- 1 -phosphate to glucose- 

 I -phosphate [9]. With the exception of FMN, in which the 

 glycone is ribitol, all these co-factor nucleotides contain 

 /i-ribose in the furanose form and phosphorylated on €'-5. 

 In co-factors composed of two nucleotides the internucleo- 

 tide bond is between the two 5-phosphate groups. 



Nucleic acids are composed of large numbers of nucleo- 

 tides and are consequently compounds of high molecular 

 weight (of the order 5 x 10^ to i x lo^), but although the indi- 

 vidual units are relatively simple, the determination of the 

 detailed structure of a nucleic acid entails the solving of 

 problems comparable in difficulty with those encountered 

 in the elucidation of the structure of a protein (cf. p. 106). 

 Depending on whether the component nucleotides contain 

 either ribose or 2-deoxyribose, nucleic acids have been 

 divided into two types, the ribose nucleic acids (RNA) and 

 the deoxyribose nucleic acids (DNA). In only three instances 

 has a derivative of ribose or 2-deoxyribose been isolated and 

 characterized, and in the absence of such evidence some 

 workers [14] prefer the terms pentose nucleic acid (PNA) 

 and deoxypentose nucleic acid (DPNA). Adenine, guanine 

 and cytosine are constituents of all the known nucleic acids, 

 and in addition a PNA contains uracil, whereas a DPNA 

 contains thymine. In consequence of their large numbers 

 of phosphate radicals, nucleic acids are highly acidic and 

 readily form salt-like compounds with bases. However, at 

 least in bacteria, the proteins associated with nucleic acids 

 in nucleoproteins are not necessarily of the basic protamine 

 or histone type [15]. 



Structure of nucleotides and nucleic acids 



Only in a few instances is there adequate proof of the 

 structure of the component nucleotides of nucleic acids, but 

 by analogy it is assumed that they all follow the same general 

 pattern. The sugar is present as the ^-isomer and in the 

 furanose form, with a glycosidic linkage between the reduc- 

 ing group (C'-i) and N-7 of the purines and N-i of the 



