Chapter 1 



INTERMEDIARY METABOLISM OF BUILDING BLOCKS 

 INVOLVED IN GROWTH' 



Saul Kit 



I. INTRODUCTION 



For growth to take place, an adequate intracellular pool of amino acids, purine 

 and pyrimidine derivatives and vitamin coenzymes must be available. The 

 requirement for these building blocks of protoplasm may be satisfied in many micro- 

 organisms and plants entirely by the synthetic activities of the organism. Thus, 

 autotrophic organisms can synthesize all of the protoplasmic constituents from 

 inorganic nitrogen and sulfur compounds and from carbon dioxide. On the other 

 hand, most organisms, including the vertebrates, cannot synthesize many of the 

 building blocks of protoplasm which hence must be supplied with the food. 

 Organisms differ with respect to their biosynthetic potentialities and therefore 

 their nutritional requirements. The same appHes to the tissues and cells of a given 

 multicellular organism. These differences reflect the enzymatic accoutrement of 

 the cells in question. For example, the inability to synthesize a given amino acid, 

 reflects the absence of a key enzyme which catalyzes the synthesis of that amino 

 acid. 



It is thus of interest to inquire into the mechanisms by which protoplasmic 

 building blocks are assembled. One of the striking results of biochemical investiga- 

 tion is the recognition that the metabolic pathways, along which chemical sub- 

 stances are utilized, are basically similar in microorganisms, fungi, plants, and 

 animals. 



A map summarizing these metabolic pathways will be found in the pocket on the 

 inner side of the back cover. This map depicts the orderly sequence of chemical 

 reactions which leads to the synthesis of amino acids, hormones, vitamins, or other 

 cellular metabolites and shows the relationships between these substances. It is to 

 be emphasized that each of the chemical reactions shown on the metabolic map 

 is catalyzed by an enzyme. However, the metabolic map summarizes the reactions 

 which take place in ^. generalized or idealized ra.ther than any actual cell. The metabolic 



^ The author would like to express his appreciation to the American Cancer Society and 

 the Leukemia Society, Inc. for research support, to Mrs. Beth Raflferty for painstaking 

 assistance in the preparation of this manuscript, and to Dr. D. N. Ward for helpful 

 criticism. Literature survey completed, January, 1957. 



Literature p. 124 



