22 : 1/ Thermodynamics of Enzyme Reactions 



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developed. The height of the peak E a is usually called the activation 

 energy. 



Figure I. Molecular collision. The solid curve represents the 

 potential energy of a molecule of A and a molecule of B when 

 separated by a distance r. It is seen that their thermal energy 

 E T is less than the activation energy E a . As a consequence 

 they cannot come close enough together to react. The 

 broken line represents their motion relative to one another. 



Figure 2. Molecular reaction. In contrast to the two mole- 

 cules depicted in Figure 1, the two here have a suffii ienl 

 thermal energy E T to come closer together than r . They 

 react at r'_ l5 releasing the energy E T + E'. 



To complete this picture, one then needs the fraction of the collisions 

 between molecules having a total internal energy greater than E a . 



