Energy Storage and Transduction in Mitochondria

Abstract

The processes of energy storage and dissipation in biological systems have been studied during the past few decades in search of alternative energy storage systems to the conventional ones. Based on these studies, living cells have proven to provide appropriate energy storage and consumption patterns for other areas of science and engineering (Alberty, 2003; Lehninger, 1984). The ability of cells to store energy in an efficient manner and to release it to gain control over the system, has made them an important target for energy related studies and modeling efforts (Qian & Beard, 2006). Since bioenergetics and biochemical thermodynamics specifically deal with energy transductions in biochemical reactions, it would be necessary to investigate these processes from a thermodynamic point of view. Living organisms usually operate at constant temperature and depend on energy from food consumption or exposure to sunlight for running their vital processes and maintaining their body temperature. Energy transduction takes place in the mitochondrion of animal cells, chloroplast of plant cells and cytoplasm of bacteria. This study focuses on bioenergetics of mitochondria, considering that membranes of mitochondria, chloroplasts and bacteria show many similarities in this regard. Mitochondria have two types of complexes for obtaining energy from substrates. Complex I includes production of NADH from oxidation of fatty acids, TCA cycle, and glycolysis. Complex II includes FADH2 production from TCA cycle. These complexes vary in different kinds of mitochondria (Cairns et al., 1998). The energy is eventually stored in the body in the form of high-energy molecules such as Adenosine Triphosphate (ATP). ATP molecules have three high-energy bonds which enable them to store energy and then release it as the bonds are broken according to the following equations (Hammes, 2000; Harper et al., 2000): ATP 髪 H態O 蝦 ADP 髪 P辿 , ΔG°旺 噺 岫伐ぬど.の岻 KJ mol ⁄ (1) ADP 髪 H態O 蝦 AMP 髪 P辿 , ΔG°旺 噺 岫伐にば.は岻 KJ/mol (2)