FERMENTATION AND RESPIRATION 



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(Readings: Weisz, pp. 319-351. S. P. T., pp. 129-132. A. L. Lehninger, "How 

 Cells Transform Energy," Sci. Am. 205, No. 3, 62-73, Sept. 1961. See also 

 R. Y. Stanier, M. DoudorofF, and E. A. Adelberg, The Microbial World, Prentice- 

 Hall, 1957, pp. 147-150, 577-583, and K. V. Thimann, Life of Bacteria, Mac- 

 millan, 1955, pp. 376-383.) 



The great metabolic processes by which cells 

 obtain energy are fermentation and respiration. 

 Fermentation is Pasteur's "life without air"; it 

 provides energy in the absence of oxygen. The 

 essence of this process is the rearrangement of 

 the atoms of a sugar to yield a compound of 

 lower energy, making the difference in energy 

 available to the cell. Respiration is a cold com- 

 bustion: molecular oxygen is used to burn or- 

 ganic molecules — frequently sugars — to yield 

 carbon dioxide, water, and exactly the same 

 total energy as if the same molecules had been 

 burned in a flame. 



In both respiration and fermentation part of 

 the energy is liberated as heat. The organism 



N=C— NH2 



I I 

 HC C— N 



\ 



O 



CH 



cannot use this, however, except to warm itself; 

 for living organisms are chemical machines, not 

 heat engines. The energy the cell needs to 

 maintain itself, to make new molecules, grow, 

 move, and reproduce, must be provided in 

 chemical form. Usually this is in the form of 

 adenosine triphosphate, ATP. It takes about 

 8 kcal of energy per mole to attach the terminal 

 phosphate group to adenosine diphosphate to 

 make ATP (ADP + P ^^ ATP), and this energy 

 is made available again when the terminal phos- 

 phate is transferred to other molecules. Such a 

 high-energy phosphate group is frequently desig- 

 nated by the symbol ~P; ATP can be written 

 AP ~ P ~ P. The terminal ~P of ATP is the 

 energy currency with which the cell pays for its 

 varied activities. 



O 



O 



o 



N— C— N- 



-C C— CH2— O— P— O— P— O— P— OH 



l\H H/H I I I 



H C— C OH OH OH 



OH OH 



ribose, a 5-C sugar 



3 phosphoric acids 



adenosine 



triphosphate 



54 



