Proteins, DNA, and other complex cellular molecules are
rich in free energy and have the potential to decompose spontaneously; that is, the laws of thermodynamics favor their breakdown. These molecules only persist because at temperatures typical for cells, few molecules can make it over the hump of activation energy. The barriers for selected reactions must occasionally be surmounted, however, for cells to carry out the processes needed for life. Heat can increase the rate of a reaction by allowing reactants to attain the transition state more often, but this would not work well in biologi
cal systems. First, high temperature denatures proteins and kills cells. Second, heat would speed up all reactions, not just those that are needed.
