THE FUNCTIONAL ORDER 



Statistically correct. But what is reproduced true to type is the 

 genetic material. The enzymatic equipment of a bacterium is far 

 from being constant. It varies quantitatively as well as qualitatively. 

 The potentialities of the organism are under the control of the 

 genetic material, but the functioning of the genetic material and 

 of the whole organism is subject to the action of the environment. 

 The organism has to cope with the environmental changes as well 

 as to ensure the harmonious interplay of its enzymes. We have to dis- 

 close the mechanism by which the genetic material is informed of 

 what happens in the cytoplasm and in the outer world. How are the 

 orders transmitted from one macromolecule to the other? What is 

 the basis of molecular interaction and balance? The cell, the inte- 

 grated system of specific interdependent macromolecules, will be 

 studied as a functional unit. As an introduction, two models will be 

 considered: one of induction of enzyme synthesis, the other of 

 inhibition of enzyme synthesis. 



Two Models of Enzyme Synthesis 



Induction. Some strains of the bacterium Escherichia coli are 

 able to utilize lactose as a carbon or energy source. Lactose is a 

 disaccharide in which glucose and galactose are united by a 

 ^-galactosidic link. The enzyme that controls its metabolism splits 

 the /?-galactosidic bond and is therefore called /3-galactosidase. As 

 a result of its activity, lactose is hydrolyzed into glucose and galac- 

 tose. This is a prerequisite for the utilization of lactose. 



Bacteria grown in a synthetic medium where the only organic 

 compound is lactose contain the enzyme galactosidase — about 6,000 

 molecules per bacterium. Bacteria grown in a medium containing 

 glycerol are completely devoid of enzyme. If lactose is supplied, 

 however, the synthesis of the galactosidase starts after a lag of a 

 few minutes, and within an hour or so each bacterium has manu- 

 factured its full load of enzyme. Thus, galactosidase is synthesized 

 only when lactose or a few other ^S-galactosides are present. Lactose 

 induces the synthesis of galactosidase. In the absence of galacto- 

 sidase, the bacteria are unable to grow in a medium containing 

 lactose as the sole carbon and energy source. When no lactose is 

 present, the enzyme is useless. The induced synthesis of the enzyme 



[37] 



