66 



METABOLIC PATHWAYS IN MICROORGANISMS 



conceptual contrivance that has made possible many ex- 

 tensions of knowledge about metabolism in general. Be- 

 cause the individual steps in the pathway have been verified, 

 the viewpoint is sometimes diminished that the cycle is 

 not only a proven piece of metabolic machinery, but also 

 may be a powerful psychological tool in helping to chart 

 new ground. 



THE MITOCHONDRION AND THE CITRIC ACID CYCLE 



The ubiquity of the Krebs cycle was given deepened ap- 

 preciation during the early 1940's, with the discovery by 



Mitochondria 



Nucleolus 



Microsomes 



Cell 

 membrane 



Fig. 3.2. Diagram of a generalized cell. 



