36 PHYSICAL FORCES AND CHEMICAL BONDS 



plcx molecules which contain great amounts of latent energy may be 

 synthesized. 



Now, if such an energy-rich molecule collides, by Brownian motion, 

 with another molecule of the right kind (and evolution has so arranged 

 matters that there is a reasonable likelihood of a molecule of the right 

 kind being in the neighborhood ) , a rearrangement of both molecules may 

 occur. If the first molecule had a carbon-carbon bond, it could be broken 

 by interacting with a molecule of phosphoric acid so that one carbon 

 receives a hydrogen from the acid, and the other atom is coupled with 

 the remaining phosphate group. This carbon-phosphate bond also has 

 appreciable energy, derived in this ease from the carbon-carbon energy 

 which now produces very little of the high velocity of separation that a 

 simple splitting would have produced. 



The way this could happen would be for the phosphoric acid to ap- 

 proach the covalent bond so closely that the electron orbits were thereby 

 disturbed. There would then be a certain probability that the covalent 

 bond would be established with the phosphate group by displacing a 

 hydrogen atom; the latter would then fall into place with the remaining 

 carbon atom. Schematically, the reaction may be written as follows: 



c— c— c— c— c— c 



+ 



H 

 O 



I 

 HO— P— OH 



II 

 O 



1 



C— C— C— H + C— C— C 



I 



o 



I 



HO— P— OH 



II 

 



The generalization then is that energy is exchanged by coupling a 

 dissociation reaction with an association reaction, with little energy loss 

 resulting. This coupling of reactions is a basic feature of biochemical 

 transformations, and in texts you find this written in general symbols as 



A^ _^B 



Here the symbolism means that the energy-releasing reaction A — » B is 

 coupled with the energy-requiring reaction C — > D. 



