2 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



our solar system there was presumably intense nuclear evolution. Two or 

 three billion years later when the intensity of nuclear radiation had abated 

 sufficiently and temperatures had subsided to near present levels, all sorts 

 of chemicals began accumulating. These compounds were synthesized by 

 various influences. Among the contributing agencies was radiation from 

 nuclear decay, as well as absorbed ultra violet radiation. Lightning was a 

 third substantial contributor, and finally the carbides, which would be 

 expected in a reducing world where oxygen had not yet been liberated by 

 photosynthesis, would yield a multitude of compounds arising from poly- 

 merization and other reactions of acetylene. With neither free atmospheric 

 oxygen nor biological enzymes to destroy the accumulating organic com- 

 pounds, all sorts of complex molecules must have appeared in ever increas- 

 ing concentrations and in widely scattered pools all over the land. 



Such molecules would react and be elaborated into all types of complex 

 systems, and since the amino acids would automatically appear in a world 

 containing NH3 , CO2 and HoO along with radiation, electrical discharges 

 and acetylene, we may suppose that eventually amino acids inevitably 

 combined to form polypeptides, and eventually even simple proteins and 

 rudimentary enzymes. Likewise phosphoric acids, the pentoses and the 

 purines, adenine and guanine, as well as the pyrimidines such as cytosine, 

 uridine and thiamine, must have accumulated and combined into rudi- 

 mentary ribonucleic and desoxyribonucleic acids. 



In this period of chemical evolution, molecules were formed with or 

 without the help of chance catalysts and were as likely to be of one optical 

 configuration as another. A general principle is of importance here. It can 

 be conveniently called the Chemical Valve Effect. Thus reaction rate 

 control can be achieved through catalytic build up of a steady state con- 

 centration of an enzyme for a second reaction. If the compound built up 

 is a powerful enzyme for a second important reaction, we have, as we shall 

 see, a machine for altering biological history. Ribonucleic acid and desoxy- 

 ribonucleic acid are, of course, catalysts for the formation of enzymes and 

 consequently are examples of this valve or gate effect. Even though a 

 catalyst is without effect on the concentrations of a system at equilibrium, 

 it may vastly change the concentration of one of the intermediates in a 

 system in a non-equilibrium steady state. This is because at equilibrium 

 every reaction is exactly balanced by its inverse and a catalyst cannot 

 change this balance since it speeds up forward and back reactions equally. 

 In contrast, a steady state is the balance reached between reactions which 

 synthesize a compound and the reactions which decompose it. Often back 

 reactions are of minor importance. Thus, if synthesizing reactions are 

 speeded up, an intermediate's concentration may be greatly increased. 



