How Biosynthetic Pathways Have Been Established

Abstract

In order to determine the pathways of biosynthesis, it is preferable to use organisms which are growing actively. Newly synthesized material can be recognized by the increase in cell numbers in a bacterial culture or the increase in weight in a growing animal such as a rat. Animal and plant cells grow slowly in general: the cells of the mammalian central nervous system grow only during the early life of the animal and is believed to divide no further; muscle cells divide and grow slowly; liver cells divide about every three months; those in the intestinal mucosa have a division time easily measured in days. In contrast, bacterial cells can double their number every twenty minutes. Newly synthesized material, in a bacterium such as E. coli, arises solely from a single carbon source such as glucose or acetate, ammonia, sulfate and inorganic phosphate. Such a bacterium is capable of intense chemical activity.