Cis-trans isomerization is an exergonic (exothermic) reaction because the energetic difference between cis and trans configuration is 3.1kJ x [mol.sup.-1] [52].

Catabolism produces energy by oxidation of fuel molecules in exergonic reactions, whereas anabolism synthesizes body components in endergonic reactions by capturing the energy released from the exergonic reaction (Mayes, 2000).

Chemical reactions that occur spontaneously are called exergonic reactions (energy yielding), and the potential energy at the end of the reaction is less than the potential energy at the beginning of the reaction.

(19) In a second approach, biological organization is a process that couples endergonic processes to the exergonic ones, therefore thermodynamically uphill processes to downhill ones.

Coenzyme M methyl reductase is the key enzyme of methanogenesis; it catalyzes the terminal and highly exergonic step of the methanogenesis pathway, the reduction and release of the coenzyme-M-bound methyl group as free methane.