Structural Model Based Comparative Analysis of Mitochondrion and Chloroplast

Abstract

Simplified network models of the essential processes in mitochondrion and in chloroplast have been derived to study the similar and different structural and functional characteristics. Based on the preliminary results the detailed analysis focused on the proton and electron transfer-related fluxes of the mitochondrial and tylakoid membrane. The model analysis extended also to the environmental connections of the two compartments. The energy production of the mitochondrial membrane results from the decomposition of organic compounds, accompanied with CO₂ production, while the hydrogen forms NADH + H⁺ and FADH₂, and the membrane processes transfer the protons and the electrons to the terminal oxidation. An associated, increased proton recycle operates the protein machine, producing ATP from ADP. The energy harnessing of the tylakoid membrane results from the photon induced decomposition of water to O₂, as well as to protons and electrons. The membrane transferred protons and electrons produce hydrogen in the form of NADPH + H⁺ for the CO₂ fixation based synthesis of the organic compounds. Here also a proton recycle operates the ATP pump. In the stroma of the chloroplast only a single reaction of the Calvin cycle takes place, while the environmental connections are organized by the storage of NADP, NADPH + H⁺, ATP and ADP. In contrary, the mitochondrial matrix involves the complete TCA (Szent-Györgyi) cycle. Having compared the structural models developed for the essential membrane processes of mitochondrion and chloroplast, it has been concluded, that the two networks determining the most important fluxes, differ from each other only the fully inversed direction of the edges. A single surplus edge in the chloroplast makes possible the formation of an additional electron cycle. In the two inverse networks the position of the ATP pump is also opposite, that makes possible the ATP production in both case.