THE DRIVE TOWARD EQUILIBRIUM 



177 



100% 

 reac tants 



Positions of Equilibrium 



© © 



© Water in high cone, salt 



(D acid + alcohol 



(3) HAc + NH4OH 



@ HCI + NaOH 



(5) salt in high cone, salt 



1 % 

 produc ts 



water in low cone, salt 

 ester + water 



NH4CI + water 



NaCI + water 



salt in low cone, salt 



Figure 7-4. Positions of Equilibrium for Several Processes. 



and 3 phosphate ions. The molecule has the following structure: 



Triphosphate part Pentose part Adenine part 



A A . A. 



r 



o 



o 



o 



■> r 



^ r 



0— p--o-p-o-P'-o--ch. 



o 



n- :h 



/ N w 



O" 



o 



o 



c 



H 



(L) 



H H C 



J .'/I 



C--C H 



I I 



OH OH 



HC 



I 

 NH 



It enters many chemical reactions in the living cell, coupling, in some un- 

 known manner, in such a way that the free energy of hydrolysis (splitting off 

 the terminal phosphate group at L), or dephosphorylation as it is often 

 called, —7.7 kcal/mole, is passed to the reaction to which it is coupled. For 

 example, adsorbed on the enzyme myosin in muscle, the molecule hy- 

 drolyzes, and the free energy appears as the mechanical work of contraction 

 of the muscle; coupled with RNA it supplies energy for protein synthesis. 

 Its hydrolysis products are adenosine diphosphate (ADP) and phosphate 

 ion(P). 



To become rephosphorylated, as it must, it is carried to the "energy fac- 

 tory" of the cell, the mitochondrion (there are 50 to 5000 of these little 

 double-membraned, 2- to 5-micron bodies per cell), and there the ADP and 

 P are coupled with some step of the respiratory enzyme's oxidation of 

 glucose by 2 , receiving the 7.7 kcal of free energy needed to force the ex- 

 pulsion of water and the regeneration of ATP. In plants, the recoupling can 

 occur photochemically through chlorophyll and its enzyme system. The re- 

 action can be represented as: 



"discharging" 



ATP + H 2 , ADP + P 



"charging" 



