36 Life: Its Nature and Origin 



cell division. All available information indicates that the manu- 

 facture proceeds along exact chemical paths and in a predetermined 

 chronological order, yet consists of the usual type of chemical reac- 

 tions: combining two molecules into one, dividing one into two, 

 or rearranging the bonds within the same compound. Thus it may 

 take dozens of steps to build up a single complex molecule. Remem- 

 bering that it occurs at relatively low temperatures, the surprising 

 feature about this synthesis is that it is so rapid. In a mosquito 

 larva, for example, practically all the cells in the full grown body 

 may arise by successive divisions of an egg in five or six days. The 

 growing tips of corn plants have been known to lengthen nearly a 

 foot overnight. A bacterial cell may mature and divide in 20 min- 

 utes. It borders on the fantastic to try to imagine the rapidity with 

 which the millions of chemical reactions must tick off in their 

 precisely ordered sequence to bring about these results. 



This apparent miracle is due to the enzymes which catalyze these 

 biological reactions at speeds far beyond their ordinary rate of oc- 

 currence at biological temperatures. About a hundred enzymes 

 have now been isolated, each one catalyzing a particular type of 

 reaction. We have no idea of the number of specific reactions in the 

 cell which require an enzyme, except that it is tremendous. We do 

 know that the same enzyme may participate in more than one re- 

 action, but presumably in each of such reactions the basic mode of 

 action is the same, for instance, the addition or removal of hydrogen 

 or the addition or removal of an —OH ion. It is of interest to note 

 that, whereas the enzyme is a large protein molecule, in at least 

 some enzymes the only known reactive part is their lone atom of iron 

 or copper in each enzyme molecule ( Mahler, Baum, and Hiibscher, 

 1956). 



Present research indicates that enzymes increase the rapidity of 

 action in the following general fashion. Suppose compounds A and 

 B are the raw materials from which the cell synthesizes essential 

 compound AB, but that A and B unite directly at only a slow rate. 

 Enzyme C, however, unites with A rapidly to form compound AC. 

 Unlike plain A, the compound AC unites rapidly with B to form AB 

 and C. Thus the two reactions A + C = AC, AC + B = AB + C, 

 progress at a fast rate to produce AB, with the original enzyme C 

 restored to its original condition. The parallel will immediately be 

 obvious between this chain of events and the action of chelating 

 compounds mentioned a few pages earlier. Each enzyme forms 

 part of a machine which will run continuously as long as A and B 



