Chapter 11 



NUCLEIC ACIDS AND 



DERIVATIVES 



Toward the end of the nineteenth century nucleic acid was established as the univer- 

 sal component of cell nuclei and recognized to be a complex high-molecular weight ma- 

 terial which could be hydrolyzed to yield a sugar, several nitrogen bases, and inorganic 

 phosphate. Later developments seemed to show that nucleic acid from animal cells was 

 characterized by having D-2-deoxyribose as its sugar constituent, while plant nucleic 

 acid had D-ribose. However, by the 1930's it became clear that plants and animals each 

 have both types of nucleic acid but that the deoxyribonucleic acid is found only in the nu- 

 cleus, and ribonucleic acid is predominantly in the cytoplasm. The earlier supposition 

 resulted from the fact that the animal cells used had been ones with a prominent nucleus 

 and little cytoplasm, while the reverse was true of the plant cells. It was early recog- 

 nized that each type of nucleic acid contains four different nitrogen bases, two purines 

 and two pyrimidines. The purines adenine and guanine and the pyrimidine cytosine are 

 common to both types of nucleic acid whereas deoxyribonucleic acid (DNA) has thymine 

 as its second pyridine base, and ribonucleic acid.(RNA) has uracil. There have been 

 reports of the occurrence of other nitrogen bases in nucleic acid from some sources. 

 The structures will be discussed in more detail in a later section. 



Partial hydrolysis of nucleic acids yields varied sized fragments known as polynu- 

 cleotides if they contain several nitrogen bases combined with sugar and phosphate, mono- 

 nucleotides if they have only one nitrogen base plus sugar and phosphate, or nucleosides 

 when they have merely a nitrogen base bound to sugar by a glycosidic bond. Smaller 

 molecules of these different types also occur as such in nature as well as being derived 

 from breakdown of nucleic acid. Some nucleotides of great physiological importance con- 

 tain nitrogen bases which are not found in the nucleic acids. They are nevertheless in- 

 cluded in this chapter. 



Very little of our present knowledge of nucleic acids and related compounds has 

 been derived from observations on the higher plants. Animal tissues and microorgan- 

 isms have been most frequently used as experimental material, and possibly some gen- 

 eralizations derived from them may not be applicable to higher plants. An attempt will 

 be made to indicate which facts are certainly known for higher plants and which are de- 

 rived from observations on other types of organisms. 



FREE PURINES AND PYRIMIDINES 



The parent substances purine and pyrimidine have the structures and ring number- 

 ing shown on the following page. 



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