S2 Microbes and You 



from the autotrophs, although this conjecture provides the sub- 

 ject for hvely discussions in seminar sessions. It should be em- 

 phasized that while it is convenient to speak of various nutritional 

 groupings of organisms, clear-cut differences do not always exist. 

 There are plenty of "in between" foiTns to complicate these neat 

 cataloguing schemes. 



If bacteria were compelled to depend upon nature to supply the 

 exact chemical substances required for their existence, survival of 

 these microscopic forms might probably be even more difficult 

 than is actuallv true under existing conditions. Whenever the 

 food particles ( molecules ) are too large for heterotrophs to absorb 

 directly, the cells must secrete digestive juices, called enzymes, 

 to attack these large molecules as the initial step in making the food 

 parcels small enough to pass through the membrane of the organ- 

 ism via the fluid menstrum. Enzymes may be defined in simple 

 language as organic catalysts^ produced by living cells. A catalyst 

 may be considered to be an agent which accelerates a chemical 

 reaction without itself being consumed in the reaction. A little bit 

 of catalyst goes a long way, and it has something which "sparks" a 

 reaction. 



The orderliness of science demands categorizing and classifica- 

 tion. Enzymes are no exceptions. We can divide these digestive 

 ferments into two major groupings, the extracellular enzymes 

 and the intracellular enzymes. When an organism is obliged 

 in its search for food to secrete enzymes to attack large molecules 

 surrounding the cell, these juices are referred to as extracellular 

 enzymes. While it is true that they are formed within the living 

 cell, such exo-enzymes are able to leave the confines of the cell and 



^ If you would like to demonstrate a catalytic reaction as a parlor trick, take 

 a piece of lump sugar and try to make it burn with the flame from a match. 

 It will not ignite. Now dip the sugar into some cigarette ash and the sugar 

 will burn with a faint blue flame when a lighted match is touched to the 

 catalyst in the cigarette ash on the lump of sugar. No doubt a good chemist 

 using micro-technics could analyze the end products of such combustion, and 

 the catalyst in the original ash would be found to be intact. To prevent 

 damage during a demonstration, it is recommended that the experimenter carry 

 out the ignition over a plate or xessel to catch any hot dripping sugar. 



