Marko E Popović, Vojin Tadić, Marijana Pantović Pavlović
Photosynthesis is among the most important sources of energy of the biosphere. An important part of photosynthesis is chlorophyll. The chemical formula of chlorophyll is well-known. However, thermodynamic properties of chlorophyll have not been reported. This paper reports enthalpies, entropies and Gibbs energies of molecules and reactions of macrocycle biosynthesis of chlorophyll a and b. The usable energy needed by plants for synthesis of chlorophyll was calculated. Chlorophyll biosynthesis reactions have negative Gibbs energy changes. This means that they are thermodynamically favorable. The negative Gibbs energy change means that the chlorophyll biosynthesis reactions could have appeared early in evolution. Gibbs energy of biosynthesis is the driving force of biosynthesis of chlorophyll that enabled the evolution of cells from the last universal common ancestor (LUCA) to cells that we know today.