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Information Storage and Neural Control 



Fig. 2. Schematic diagram of the energy cycle of an ecosystem, modified and 



expanded after Szent-Gyorgi (25) and Arnon (26). Anaerobic and chemosyn- 



thetic processes are not indicated. 



sequently reduce one of two pyridine nucleotides {PN -^ PNHi, 

 Fig. 2). Concurrently, ATP is synthesized, incorporating into its 

 terminal "high energy" phosphate bond some of the original 

 photon energy. Neither ATP, DPN, nor TPN is stable enough 

 to function in energy storage. This is accomplished by reducing 

 CO 2 to carbohydrates and water, then to lipids (Fig. 2). 



Energy so stored may be utiHzed directly by the primary pro- 

 ducer, or it may be transmitted to other organisms in the food 

 chain. The retrieval of energy from storage is accomplished by 

 transferring electrons (in H atoms) to PN, releasing the carbon 

 as CO 2. The PNHi then transfers electrons to flavin mononucleo- 

 tide (FMN), whence they cascade down the oxidative chain of 

 cytochromes, generating heat at every step. Most of the energy 

 remaining is converted (in oxidative phosphorylation) to .4 TP, 

 in which form it is available for the performance of cellular work. 

 Finally, the electrons are transferred to Oo which then binds 

 protons to form HoO. Water represents ground state, where the 

 cycle e~ —> e* -^ e^ is completed. If, at a specified time, the 

 system contains more free energy than it did at a prior time, we 

 say that a favorable balance between inputs and expenditures has 



